Sun Services Java™ Programming Language SL-275 Java™ Programming Language
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Course Contents About This Course ..................................................................................... Preface-xvi Course Goals .............................................................................................................................Preface-xvii Course Overview ...................................................................................................................... Preface-xix Course Map .......................................................................
Sun Services Compile-Time Errors ............................................................................................................................ 1-21 Runtime Errors ...................................................................................................................................... 1-22 Java Technology Runtime Environment ........................................................................................... 1-23 Object-Oriented Programming ................................
Sun Services Identifiers, Keywords, and Types ........................................................................... 3-1 Objectives ................................................................................................................................................. 3-2 Relevance .................................................................................................................................................. 3-4 Comments .......................................................
Sun Services Variable Initialization ............................................................................................................................. 4-7 Initialization Before Use Principle ........................................................................................................ 4-8 Operator Precedence .............................................................................................................................. 4-9 Logical Operators ...............................
Sun Services Using the Enhanced for Loop ............................................................................................................ 5-13 Array Resizing ....................................................................................................................................... 5-14 Copying Arrays ..................................................................................................................................... 5-15 Class Design .................................
Sun Services Wrapper Classes .................................................................................................................................... 6-41 Autoboxing of Primitive Types ........................................................................................................... 6-43 Advanced Class Features ....................................................................................... 7-1 Objectives ..........................................................................
Sun Services The try-catch Statement ..................................................................................................................... 8-7 Call Stack Mechanism .......................................................................................................................... 8-10 The finally Clause ............................................................................................................................. 8-11 Exception Categories .................................
Sun Services File Stream I/O ...................................................................................................................................... 9-20 File Output Example ............................................................................................................................. 9-23 The Collections API .............................................................................................................................. 9-25 A Set Example ..........................
Sun Services The BorderLayout Manager ............................................................................................................. 10-24 Organization of the Border Layout Components ........................................................................... 10-25 The BorderExample Class ................................................................................................................. 10-26 Example of BorderLayout ...............................................................
Sun Services How to Create a Menu ......................................................................................................................... 12-9 Creating a MenuBar ............................................................................................................................. 12-10 Creating a Menu ................................................................................................................................... 12-11 Creating a MenuItem ..........................
Sun Services Monitor Model for Synchronization ................................................................................................ 13-28 The Producer Class ............................................................................................................................ 13-29 The Consumer Class ............................................................................................................................ 13-31 The SyncStack Class ..........................................
Sun Services Networking .............................................................................................................. 15-1 Objectives ............................................................................................................................................... 15-2 Relevance ................................................................................................................................................ 15-3 Networking .........................................
Sun Services Preface About This Course Java™ Programming Language
Sun Services Course Goals This course provides you with knowledge and skills to: • Create Java™ technology applications that leverage the object-oriented features of the Java language, such as encapsulation, inheritance, and polymorphism • Execute a Java technology application from the command-line • Use Java technology data types and expressions • Use Java technology flow control constructs • Use arrays and other data collections • Implement error-handling techniques using exception handling Java™ Program
Sun Services Course Goals • Create an event-driven graphical user interface (GUI) by using Java technology GUI components: panels, buttons, labels, text fields, and text areas • Implement input/output (I/O) functionality to read from and write to data and text files • Create multithreaded programs • Create a simple Transmission Control Protocol/ Internet Protocol (TCP/IP) client that communicates through sockets Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Course Overview This course describes the following areas: • The syntax of the Java programming language • Object-oriented concepts as they apply to the Java programming language • GUI programming • Multithreading • Networking Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Course Map The Java Programming Language Basics Getting Started Identifiers, Keywords, and Types Object-Oriented Programming Expressions Arrays and Flow Control More Object-Oriented Programming Advanced Class Design Class Features Building Applications Exceptions Text-Based and Assertions Applications Developing Graphical User Interfaces Building Java GUI Event GUI-Based GUIs Handling Applications Advanced Java Programming Threads Advanced I/O Streams Java™ Programming Lan
Sun Services Topics Not Covered • Object-oriented analysis and design – Covered in OO-226: Object-Oriented Application Analysis and Design Using UML • General programming concepts – Covered in SL-110: Fundamentals of the Java™ Programming Language Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services How Prepared Are You? Before attending this course, you should have completed SL-110: Fundamentals of the Java™ Programming Language, or have: • Created and compiled programs with C or C++ • Created and edited text files using a text editor • Used a World Wide Web (WWW) browser, such as Netscape Navigator™ Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Introductions • • • • • • Name Company affiliation Title, function, and job responsibility Experience related to topics presented in this course Reasons for enrolling in this course Expectations for this course Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services How to Use the Icons Additional resources ! Discussion ? Note Caution Visual Aid Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Typographical Conventions and Symbols • Courier is used for the names of commands, files, directories, programming code, programming constructs, and on-screen computer output. • Courier bold is used for characters and numbers that you type, and for each line of programming code that is referenced in a textual description. • Courier italics is used for variables and command-line placeholders that are replaced with a real name or value.
Sun Services Typographical Conventions and Symbols • Palatino italics is used for book titles, new words or terms, or words that are emphasized. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Additional Conventions Java programming language examples use the following additional conventions: • Courier is used for the class names, methods, and keywords. • Methods are not followed by parentheses unless a formal or actual parameter list is shown. • Line breaks occur where there are separations, conjunctions, or white space in the code. • If a command on the Solaris™ Operating System (Solaris OS) is different from the Microsoft Windows platform, both commands are shown.
Sun Services Module 1 Getting Started Java™ Programming Language
Sun Services Objectives • Describe the key features of Java technology • Write, compile, and run a simple Java technology application • Describe the function of the Java Virtual Machine (JVM™) • Define garbage collection • List the three tasks performed by the Java platform that handle code security NOTE: The terms “Java Virtual Machine” and “JVM” mean a Virtual Machine for the Java™ platform. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance • Is the Java programming language a complete language or is it useful only for writing programs for the Web? • Why do you need another programming language? • How does the Java technology platform improve on other language platforms? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services What Is the Java™ Technology? • Java technology is: • A programming language • A development environment • An application environment • A deployment environment • It is similar in syntax to C++. • It is used for developing both applets and applications. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Primary Goals of the Java Technology • Provides an easy-to-use language by: • Avoiding many pitfalls of other languages • Being object-oriented • Enabling users to create streamlined and clear code • Provides an interpreted environment for: • Improved speed of development • Code portability Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Primary Goals of the Java Technology • Enables users to run more than one thread of activity • Loads classes dynamically; that is, at the time they are actually needed • Supports changing programs dynamically during runtime by loading classes from disparate sources • Furnishes better security Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Primary Goals of the Java Technology The following features fulfill these goals: • • • • The Java Virtual Machine (JVM™)1 Garbage collection The Java Runtime Environment (JRE) JVM tool interface 1. The terms "Java Virtual Machine" and "JVM" mean a Virtual Machine for the Java platform Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Java Virtual Machine • Provides hardware platform specifications • Reads compiled byte codes that are platform-independent • Is implemented as software or hardware • Is implemented in a Java technology development tool or a Web browser Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Java Virtual Machine JVM provides definitions for the: • • • • • • • • Instruction set (central processing unit [CPU]) Register set Class file format Stack Garbage-collected heap Memory area Fatal error reporting High-precision timing support Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Java Virtual Machine • The majority of type checking is done when the code is compiled. • Implementation of the JVM approved by Sun Microsystems must be able to run any compliant class file. • The JVM executes on multiple operating environments. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Garbage Collection • Allocated memory that is no longer needed should be deallocated. • In other languages, deallocation is the programmer’s responsibility. • The Java programming language provides a system-level thread to track memory allocation. • Garbage collection has the following characteristics: • Checks for and frees memory no longer needed • Is done automatically • Can vary dramatically across JVM implementations Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services The Java Runtime Environment The Java application environment performs as follows: Compile Runtime java Class loader TestGreeting.java javac Load from hard disk, network, or other source Bytecode verifier Interpreter TestGreeting.class Runtime Hardware Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Operation of the JRE With a Just-In-Time (JIT) Compiler Compile Runtime Class loader java TestGreeting.java javac Load from hard disk, network, or other source Bytecode verifier Interpreter TestGreeting.class JIT code generator Runtime Hardware Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services JVM™ Tasks The JVM performs three main tasks: • Loads code • Verifies code • Executes code Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Class Loader • Loads all classes necessary for the execution of a program • Maintains classes of the local file system in separate namespaces • Prevents spoofing Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Bytecode Verifier Ensures that: • The code adheres to the JVM specification. • The code does not violate system integrity. • The code causes no operand stack overflows or underflows. • The parameter types for all operational code are correct. • No illegal data conversions (the conversion of integers to pointers) have occurred. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services A Simple Java Application The TestGreeting.java Application 1 2 3 4 5 6 7 8 9 // // Sample "Hello World" application // public class TestGreeting{ public static void main (String[] args) { Greeting hello = new Greeting(); hello.greet(); } } The Greeting.java Class 1 2 3 4 5 public class Greeting { public void greet() { System.out.println(“hi”); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The TestGreeting Application • • • • Comment lines Class declaration The main method Method body Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Greeting Class • Class declaration • The greet method Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Compiling and Running the TestGreeting Program • Compile TestGreeting.java: javac TestGreeting.java • The Greeting.java is compiled automatically. • Run the application by using the following command: java TestGreeting • Locate common compile and runtime errors. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Compile-Time Errors • javac: Command not found • Greeting.java:4: cannot resolve symbol symbol : method printl (java.lang.String) location: class java.io.PrintStream System.out.printl("hi"); ^ • TestGreet.java:4: Public class TestGreeting must be defined in a file called "TestGreeting.java". Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Runtime Errors • Can’t find class TestGreeting • Exception in thread "main" java.lang.NoSuchMethodError: main Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Compile Java Technology Runtime Environment TestGreeting.java Also compiles javac TestGreeting.class java Runtime Greeting.java Greeting.class Also loads JVM Can run on multiple platforms UNIX® DOS JVM JVM Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 2 Object-Oriented Programming Java™ Programming Language
Sun Services Objectives • Define modeling concepts: abstraction, encapsulation, and packages • Discuss why you can reuse Java technology application code • Define class, member, attribute, method, constructor, and package • Use the access modifiers private and public as appropriate for the guidelines of encapsulation • Invoke a method on a particular object • Use the Java technology application programming interface (API) online documentation Java™ Programming Language Copyright 2005 Sun Microsystems, Inc
Sun Services Relevance • What is your understanding of software analysis and design? • What is your understanding of design and code reuse? • What features does the Java programming language possess that make it an object-oriented language? • Define the term object-oriented. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Software Engineering Toolkits / Frameworks / Object APIs (1990s–Up) Java 2 SDK AWT / J.F.C.
Sun Services The Analysis and Design Phase • Analysis describes what the system needs to do: Modeling the real-world, including actors and activities, objects, and behaviors • Design describes how the system does it: • Modeling the relationships and interactions between objects and actors in the system • Finding useful abstractions to help simplify the problem or solution Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Abstraction • Functions – Write an algorithm once to be used in many situations • Objects – Group a related set of attributes and behaviors into a class • Frameworks and APIs – Large groups of objects that support a complex activity; Frameworks can be used as is or be modified to extend the basic behavior Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Classes as Blueprints for Objects • In manufacturing, a blueprint describes a device from which many physical devices are constructed. • In software, a class is a description of an object: • A class describes the data that each object includes. • A class describes the behaviors that each object exhibits.
Sun Services Declaring Java Technology Classes • Basic syntax of a Java class: * class { * * * } • Example: 1 2 3 4 5 6 public class Vehicle { private double maxLoad; public void setMaxLoad(double value) { maxLoad = value; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Declaring Attributes • Basic syntax of an attribute: * [ = ]; • Examples: 1 2 3 4 5 public class Foo { private int x; private float y = 10000.0F; private String name = "Bates Motel"; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Declaring Methods • Basic syntax of a method: * ( * ) { * } • Examples: 1 2 3 4 5 6 7 8 9 10 11 public class Dog { private int weight; public int getWeight() { return weight; } public void setWeight(int newWeight) { if ( newWeight > 0 ) { weight = newWeight; } } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Accessing Object Members • The dot notation is:
Sun Services Information Hiding The problem: MyDate +day : int +month : int +year : int Client code has direct access to internal data (d refers to a MyDate object): d.day = 32; // invalid day d.month = 2; d.day = 30; // plausible but wrong d.day = d.day + 1; // no check for wrap around Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Information Hiding The solution: MyDate -day : int -month : int -year : int Client code must use setters and getters to access internal data: MyDate d = new MyDate(); +getDay() : int +getMonth() : int +getYear() : int +setDay(int) : boolean +setMonth(int) : boolean +setYear(int) : boolean d.setDay(32); // invalid day, returns false d.setMonth(2); d.setDay(30); // plausible but wrong, // setDay returns false Verify days in month d.setDay(d.
Sun Services Encapsulation • Hides the implementation details of a class • Forces the user to use an interface to access data • Makes the code more maintainable MyDate -date : long +getDay() : int +getMonth() : int +getYear() : int +setDay(int) : boolean +setMonth(int) : boolean +setYear(int) : boolean -isDayValid(int) : boolean Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Declaring Constructors • Basic syntax of a constructor: [] ( * ) { * } • Example: 1 2 3 4 5 6 7 8 public class Dog { private int weight; public Dog() { weight = 42; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Default Constructor • There is always at least one constructor in every class. • If the writer does not supply any constructors, the default constructor is present automatically: • The default constructor takes no arguments • The default constructor body is empty • The default enables you to create object instances with new Xxx()without having to write a constructor. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Source File Layout • Basic syntax of a Java source file is: [] * + • For example, the VehicleCapacityReport.java file is: 1 2 3 4 5 6 7 8 9 10 package shipping.reports; import shipping.domain.*; import java.util.List; import java.io.*; public class VehicleCapacityReport { private List vehicles; public void generateReport(Writer output) {...} } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Software Packages • Packages help manage large software systems. • Packages can contain classes and sub-packages. shipping gui domain Company reports Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision F Owns 0..
Sun Services The package Statement • Basic syntax of the package statement is: package [.]*; • Examples of the statement are: package shipping.gui.reportscreens; • Specify the package declaration at the beginning of the source file. • Only one package declaration per source file. • If no package is declared, then the class is placed into the default package. • Package names must be hierarchical and separated by dots.
Sun Services The import Statement • Basic syntax of the import statement is: import [.]*.; OR import [.]*.*; • Examples of the statement are: import java.util.List; import java.io.*; import shipping.gui.reportscreens.*; • The import statement does the following: • Precedes all class declarations • Tells the compiler where to find classes Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Directory Layout and Packages • Packages are stored in the directory tree containing the package name. • An example is the shipping application packages. shipping/ domain/ Company.class Vehicle.class RiverBarge.class Truck.class gui/ reports/ VehicleCapacityReport.class Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Development JavaProjects/ ShippingPrj/ src/ shipping/ domain/ gui/ reports/ docs/ classes/ shipping/ domain/ gui/ reports/ Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Compiling Using the -d Option cd JavaProjects/ShippingPrj/src javac -d ../classes shipping/domain/*.java Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Terminology Recap • Class – The source-code blueprint for a run-time object • Object – An instance of a class; also known as instance • Attribute – A data element of an object; also known as data member, instance variable, and data field • Method – A behavioral element of an object; also known as algorithm, function, and procedure • Constructor – A method-like construct used to initialize a new object • Package – A grouping of classes and sub-packages Java™ Programming Language Copyright 2005
Sun Services Using the Java Technology API Documentation • A set of Hypertext Markup Language (HTML) files provides information about the API. • A frame describes a package and contains hyperlinks to information describing each class in that package. • A class document includes the class hierarchy, a description of the class, a list of member variables, a list of constructors, and so on. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 2, slide 26 of 26 Java Technology API Documentation With HTML3 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 3 Identifiers, Keywords, and Types Java™ Programming Language
Sun Services Objectives • • • • • • Use comments in a source program Distinguish between valid and invalid identifiers Recognize Java technology keywords List the eight primitive types Define literal values for numeric and textual types Define the terms primitive variable and reference variable Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Objectives • • • • • Declare variables of class type Construct an object using new Describe default initialization Describe the significance of a reference variable State the consequences of assigning variables of class type Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance • Do you know the primitive Java types? • Can you describe the difference between variables holding primitive values as compared with object references? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Comments The three permissible styles of comment in a Java technology program are: // comment on one line /* comment on one * or more lines */ /** documentation comment * can also span one or more lines */ Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Semicolons, Blocks, and White Space • A statement is one or more lines of code terminated by a semicolon (;): totals = a + b + c + d + e + f; • A block is a collection of statements bound by opening and closing braces: { x = y + 1; y = x + 1; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Semicolons, Blocks, and White Space • A class definition uses a special block: public class MyDate { private int day; private int month; private int year; } • You can nest block statements. while ( i < large ) { a = a + i; // nested block if ( a == max ) { b = b + a; a = 0; } i = i + 1; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Semicolons, Blocks, and White Space • Any amount of white space is permitted in a Java program. For example: {int x;x=23*54;} is equivalent to: { int x; x = 23 * 54; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Identifiers Identifiers have the following characteristics: • Are names given to a variable, class, or method • Can start with a Unicode letter, underscore (_), or dollar sign ($) • Are case-sensitive and have no maximum length • Examples: identifier userName user_name _sys_var1 $change Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Java Programming Language Keywords abstract continue for new switch assert default goto package synchronized boolean do if private this break double implements protected throw byte else import public throws case enum instanceof return transient catch extends int short try char final interface static void class finally long strictfp volatile const float native super while Reserved literal words: null, true, and false Java™ Programming Language
Sun Services Primitive Types The Java programming language defines eight primitive types: • • • • Logical – boolean Textual – char Integral – byte, short, int, and long Floating – double and float Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Logical – boolean The boolean primitive has the following characteristics: • The boolean data type has two literals, true and false. • For example, the statement: boolean truth = true; declares the variable truth as boolean type and assigns it a value of true. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Textual – char The textual char primitive has the following characteristics: • Represents a 16-bit Unicode character • Must have its literal enclosed in single quotes (’ ’) • Uses the following notations: 'a' The letter a '\t' The tab character '\u????' A specific Unicode character, ????, is replaced with exactly four hexadecimal digits . For example, ’\u03A6’ is the Greek letter phi [Φ]. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Textual – String The textual String type has the following characteristics: • Is not a primitive data type; it is a class • Has its literal enclosed in double quotes (" ") "The quick brown fox jumps over the lazy dog." • Can be used as follows: String greeting = "Good Morning !! \n"; String errorMessage = "Record Not Found !"; Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Integral – byte, short, int, and long The integral primitives have the following characteristics: • Integral primates use three forms: Decimal, octal, or hexadecimal 2 The decimal form for the integer 2. 077 The leading 0 indicates an octal value. 0xBAAC The leading 0x indicates a hexadecimal value. • Literals have a default type of int. • Literals with the suffix L or l are of type long. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Integral – byte, short, int, and long • Integral data types have the following ranges: Integer Length Name or Type Range 8 bits byte -27 to 27-1 16 bits short -215 to 215 -1 32 bits int -231 to 231 -1 64 bits long -263 to 263 -1 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Floating Point – float and double The floating point primitives have the following characteristics: • Floating-point literal includes either a decimal point or one of the following: • E or e (add exponential value) • F or f (float) • D or d (double) 3.14 A simple floating-point value (a double) 6.02E23 A large floating-point value 2.718F A simple float size value 123.4E+306D A large double value with redundant D Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Floating Point – float and double • Literals have a default type of double. • Floating-point data types have the following sizes: Float Length Name or Type 32 bits float 64 bits double Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Sun Services Variables, Declarations, and Assignments } Module 3, slide 19 of 37 public class Assign { public static void main (String args []) { // declare integer variables int x, y; // declare and assign floating point float z = 3.414f; // declare and assign double double w = 3.
Sun Services Java Reference Types • In Java technology, beyond primitive types all others are reference types. • A reference variable contains a handle to an object. • For example: 1 2 3 4 5 6 7 public class MyDate { private int day = 1; private int month = 1; private int year = 2000; public MyDate(int day, int month, int year) { ... } public String toString() { ...
Sun Services Constructing and Initializing Objects • Calling new Xyz() performs the following actions: a. Memory is allocated for the object. b. Explicit attribute initialization is performed. c. A constructor is executed. d. The object reference is returned by the new operator. • The reference to the object is assigned to a variable. • An example is: MyDate my_birth = new MyDate(22, 7, 1964); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Memory Allocation and Layout • A declaration allocates storage only for a reference: MyDate my_birth = new MyDate(22, 7, 1964); my_birth ???? • Use the new operator to allocate space for MyDate: MyDate my_birth = new MyDate(22, 7, 1964); my_birth ???? day 0 month 0 year 0 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Explicit Attribute Initialization • Initialize the attributes as follows: MyDate my_birth = new MyDate(22, 7, 1964); my_birth ???? day 1 month 1 year 2000 • The default values are taken from the attribute declaration in the class. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Executing the Constructor • Execute the matching constructor as follows: MyDate my_birth = new MyDate(22, 7, 1964); my_birth ???? day 22 month 7 year 1964 • In the case of an overloaded constructor, the first constructor can call another. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Assigning a Variable • Assign the newly created object to the reference variable as follows: MyDate my_birth = new MyDate(22, 7, 1964); my_birth 0x01abcdef day 22 month 7 year 1964 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Assigning References • Two variables refer to a single object: 1 2 3 4 int x = 7; int y = x; MyDate s = new MyDate(22, 7, 1964); MyDate t = s; x 7 y 7 s 0x01234567 t 0x01234567 22 7 1964 • Reassignment makes two variables point to two objects: 5 t = new MyDate(22, 12, 1964); x 7 y 7 s 0x01234567 t 0x12345678 22 7 1964 22 12 1964 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Pass-by-Value • In a single virtual machine, the Java programming language only passes arguments by value. • When an object instance is passed as an argument to a method, the value of the argument is a reference to the object. • The contents of the object can be changed in the called method, but the original object reference is never changed. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Pass-by-Value 1 2 3 4 5 6 7 8 9 10 11 12 public class PassTest { // Methods to change the current values public static void changeInt(int value) { value = 55; } public static void changeObjectRef(MyDate ref) { ref = new MyDate(1, 1, 2000); } public static void changeObjectAttr(MyDate ref){ ref.setDay(4); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Pass-by-Value 13 14 15 16 17 18 19 20 21 22 23 public static void main(String args[]) { MyDate date; int val; // Assign the int val = 11; // Try to change it changeInt(val); // What is the current value? System.out.println("Int value is: " + val); The result of this output is: Int value is: 11 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Pass-by-Value 24 25 26 27 28 29 30 // Assign the date date = new MyDate(22, 7, 1964); // Try to change it changeObjectRef(date); // What is the current value? System.out.println("MyDate: " + date); The result of this output is: MyDate: 22-7-1964 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Pass-by-Value 31 32 33 34 35 36 37 38 // Now change the day attribute // through the object reference changeObjectAttr(date); // What is the current value? System.out.println("MyDate: " + date); } } The result of this output is: MyDate: 4-7-1964 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The this Reference Here are a few uses of the this keyword: • To resolve ambiguity between instance variables and parameters • To pass the current object as a parameter to another method or constructor Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The this Reference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class MyDate { private int day = 1; private int month = 1; private int year = 2000; public MyDate(int day, int month, int year) { this.day = day; this.month = month; this.year = year; } public MyDate(MyDate date) { this.day = date.day; this.month = date.month; this.year = date.year; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The this Reference 16 17 18 19 20 21 22 23 24 25 26 public MyDate addDays(int moreDays) { MyDate newDate = new MyDate(this); newDate.day = newDate.day + moreDays; // Not Yet Implemented: wrap around code... return newDate; } public String toString() { return "" + day + "-" + month + "-" + year; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The this Reference 1 2 3 4 5 6 7 8 public class TestMyDate { public static void main(String[] args) { MyDate my_birth = new MyDate(22, 7, 1964); MyDate the_next_week = my_birth.addDays(7); System.out.println(the_next_week); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Java Programming Language Coding Conventions • Packages: com.example.domain; • Classes, interfaces, and enum types: SavingsAccount • Methods: getAccount() • Variables: currentCustomer • Constants: HEAD_COUNT Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Java Programming Language Coding Conventions • Control structures: if ( condition ) { statement1; } else { statement2; } • Spacing: • Use one statement per line. • Use two or four spaces for indentation. • Comments: • Use // to comment inline code. • Use /** documentation */ for class members. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 4 Expressions and Flow Control Java™ Programming Language
Sun Services Objectives • Distinguish between instance and local variables • Describe how to initialize instance variables • Identify and correct a Possible reference before assignment compiler error • Recognize, describe, and use Java software operators • Distinguish between legal and illegal assignments of primitive types Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Objectives • Identify boolean expressions and their requirements in control constructs • Recognize assignment compatibility and required casts in fundamental types • Use if, switch, for, while, and do constructions and the labeled forms of break and continue as flow control structures in a program Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance • What types of variables are useful to programmers? • Can multiple classes have variables with the same name and, if so, what is their scope? • What types of control structures are used in other languages? What methods do these languages use to control flow? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Variables and Scope Local variables are: • Variables that are defined inside a method and are called local, automatic, temporary, or stack variables • Variables that are created when the method is executed are destroyed when the method is exited Variable initialization comprises the following: • Local variables require explicit initialization. • Instance variables are initialized automatically. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Variable Scope Example public class ScopeExample { private int i=1; Execution Stack public void firstMethod() { int i=4, j=5; Heap Memory this.i = i + j; secondMethod(7); } public void secondMethod(int i) { int j=8; this.i = i + j; } secondMethod j 8 i 7 this j firstMethod } i ScopeExample 5 i 1 4 this main scope public class TestScoping { public static void main(String[] args) { ScopeExample scope = new ScopeExample(); scope.
Sun Services Variable Initialization Variable Value byte 0 short 0 int 0 long 0L float 0.0F double 0.0D char '\u0000' boolean false All reference types null Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Initialization Before Use Principle The compiler will verify that local variables have been initialized before used. 3 4 5 6 7 8 9 10 11 public void doComputation() { int x = (int)(Math.random() * 100); int y; int z; if (x > 50) { y = 9; } z = y + x; // Possible use before initialization } javac TestInitBeforeUse.java TestInitBeforeUse.
Sun Services Operator Precedence Operators Associative ++ -- + unary - unary ~ ! () * / % + << >> >>> < > <= >= instanceof == != & ^ | && || ? : = *= /= %= += -= <<= >>= >>>= &= ^= |= R to L L to R L to R L to R L to R L to R L to R L to R L to R L to R L to R R to L R to L Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Logical Operators • The boolean operators are: ! – NOT | – OR & – AND ^ – XOR • The short-circuit boolean operators are: && – AND || – OR • You can use these operators as follows: MyDate d = reservation.getDepartureDate(); if ( (d != null) && (d.day > 31) { // do something with d } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Bitwise Logical Operators • The integer bitwise operators are: ~ – Complement ^ – XOR & – AND | – OR • Byte-sized examples include: 0 0 1 0 1 1 0 1 ~ 0 1 0 0 1 1 1 1 & 0 1 0 0 1 1 1 1 1 0 1 1 0 0 0 0 0 0 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 ^ 0 1 0 0 1 1 1 1 | 0 1 0 0 1 1 1 1 0 1 1 0 0 0 1 0 0 1 1 0 1 1 1 1 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Right-Shift Operators >> and >>> • Arithmetic or signed right shift (>>) operator: • Examples are: 128 >> 1 returns 128/21 256 >> 4 returns 256/24 -256 >> 4 returns -256/24 = 64 = 16 = -16 • The sign bit is copied during the shift. • Logical or unsigned right-shift (>>>) operator: • This operator is used for bit patterns. • The sign bit is not copied during the shift. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Left-Shift Operator << • Left-shift (<<) operator works as follows: 128 << 1 returns 128 * 21 = 256 16 << 2 returns 16 * 22 = 64 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Shift Operator Examples 1357 = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 0 1 1 0 1 -1357 = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 1357 >> 5 = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 -1357 >> 5 = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1357 >>> 5 = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 -1357 >>> 5 = 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1357 << 5 = 0 0
Sun Services String Concatenation With + • The + operator works as follows: • Performs String concatenation • Produces a new String: String salutation = "Dr."; String name = "Pete" + " " + "Seymour"; String title = salutation + " " + name; • One argument must be a String object. • Non-strings are converted to String objects automatically. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Casting • If information might be lost in an assignment, the programmer must confirm the assignment with a cast. • The assignment between long and int requires an explicit cast. long bigValue = 99L; int squashed = bigValue; // Wrong, needs a cast int squashed = (int) bigValue; // OK int squashed = 99L; int squashed = (int) 99L; int squashed = 99; Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision F // Wrong, needs a cast // OK, but...
Sun Services Promotion and Casting of Expressions • Variables are promoted automatically to a longer form (such as int to long). • Expression is assignment-compatible if the variable type is at least as large (the same number of bits) as the expression type. long bigval = 6; int smallval = 99L; // 6 is an int type, OK // 99L is a long, illegal double z = 12.414F; float z1 = 12.414; // 12.414F is float, OK // 12.414 is double, illegal Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Simple if, else Statements The if statement syntax: if ( ) Example: if ( x < 10 ) System.out.println("Are you finished yet?"); or (recommended): if ( x < 10 ) { System.out.println("Are you finished yet?"); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Complex if, else Statements The if-else statement syntax: if ( ) else Example: if ( x < 10 ) { System.out.println("Are you finished yet?"); } else { System.out.println("Keep working..."); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Complex if, else Statements The if-else-if statement syntax: if ( ) else if ( ) Example: int count = getCount(); // a method defined in the class if (count < 0) { System.out.println("Error: count value is negative."); } else if (count > getMaxCount()) { System.out.println("Error: count value is too big."); } else { System.out.println("There will be " + count + " people for lunch today.
Sun Services Switch Statements The switch statement syntax: switch ( ) { case : * [break;] case : * [break;] default: * [break;] } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Switch Statements A switch statement example: switch ( carModel ) { case DELUXE: addAirConditioning(); addRadio(); addWheels(); addEngine(); break; case STANDARD: addRadio(); addWheels(); addEngine(); break; default: addWheels(); addEngine(); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Switch Statements This switch statement is equivalent to the previous example: switch ( carModel ) { case DELUXE: addAirConditioning(); case STANDARD: addRadio(); default: addWheels(); addEngine(); } Without the break statements, the execution falls through each subsequent case clause. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Looping Statements The for loop: for ( ; ; ) Example: for ( int i = 0; i < 10; i++ ) System.out.println(i + " squared is " + (i*i)); or (recommended): for ( int i = 0; i < 10; i++ ) { System.out.println(i + " squared is " + (i*i)); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Looping Statements The while loop: while ( ) Example: int i = 0; while ( i < 10 ) { System.out.println(i + " squared is " + (i*i)); i++; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Looping Statements The do/while loop: do while ( ); Example: int i = 0; do { System.out.println(i + " squared is " + (i*i)); i++; } while ( i < 10 ); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Special Loop Flow Control • The break [
Sun Services The break Statement 1 2 3 4 5 6 7 do { statement; if ( condition ) { break; } statement; } while ( test_expr ); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The continue Statement 1 2 3 4 5 6 7 do { statement; if ( condition ) { continue; } statement; } while ( test_expr ); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Using break Statements with Labels 1 2 3 4 5 6 7 8 9 10 11 12 outer: do { statement1; do { statement2; if ( condition ) { break outer; } statement3; } while ( test_expr ); statement4; } while ( test_expr ); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Using continue Statements with Labels 1 2 3 4 5 6 7 8 9 10 11 12 test: do { statement1; do { statement2; if ( condition ) { continue test; } statement3; } while ( test_expr ); statement4; } while ( test_expr ); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 5 Arrays Java™ Programming Language
Sun Services Objectives • Declare and create arrays of primitive, class, or array types • Explain why elements of an array are initialized • Explain how to initialize the elements of an array • Determine the number of elements in an array • Create a multidimensional array • Write code to copy array values from one array to another Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance What is the purpose of an array? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Declaring Arrays • Group data objects of the same type. • Declare arrays of primitive or class types: char s[]; Point p[]; char[] s; Point[] p; • Create space for a reference. • An array is an object; it is created with new. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating Arrays Use the new keyword to create an array object. For example, a primitive (char) array: 1 2 3 4 5 6 7 8 9 10 public char[] createArray() { char[] s; s = new char[26]; for ( int i=0; i<26; i++ ) { s[i] = (char) (’A’ + i); } return s; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating an Array of Character Primitives Execution Stack Heap Memory char[] A B C D createArray s this Z main Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating Reference Arrays Another example, an object array: 1 2 3 4 5 6 7 8 9 10 public Point[] createArray() { Point[] p; p = new Point[10]; for ( int i=0; i<10; i++ ) { p[i] = new Point(i, i+1); } return p; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating an Array of Character Primitives With Point Objects Execution Stack Heap Memory Point Point[] x y 0 1 Point x y createArray 1 2 p Point this main Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Initializing Arrays • Initialize an array element. • Create an array with initial values.
Sun Services Multidimensional Arrays Arrays of arrays: int[][] twoDim = new int[4][]; twoDim[0] = new int[5]; twoDim[1] = new int[5]; int[][] twoDim = new int[][4]; // illegal Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Multidimensional Arrays • Non-rectangular arrays of arrays: twoDim[0] twoDim[1] twoDim[2] twoDim[3] = = = = new new new new int[2]; int[4]; int[6]; int[8]; • Array of four arrays of five integers each: int[][] twoDim = new int[4][5]; Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Array Bounds All array subscripts begin at 0: public void printElements(int[] list) { for (int i = 0; i < list.length; i++) { System.out.println(list[i]); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Using the Enhanced for Loop Java 2 Platform, Standard Edition (J2SE™) version 5.0 introduced an enhanced for loop for iterating over arrays: public void printElements(int[] list) { for ( int element : list ) { System.out.println(element); } } The for loop can be read as for each element in list do. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Array Resizing • You cannot resize an array. • You can use the same reference variable to refer to an entirely new array, such as: int[] myArray = new int[6]; myArray = new int[10]; Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Copying Arrays The System.arraycopy() method to copy arrays is: 1 2 3 4 5 6 7 8 9 //original array int[] myArray = { 1, 2, 3, 4, 5, 6 }; // new larger array int[] hold = { 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 }; // copy all of the myArray array to the hold // array, starting with the 0th index System.arraycopy(myArray, 0, hold, 0, myArray.length); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 6 Class Design Java™ Programming Language
Sun Services Objectives • Define inheritance, polymorphism, overloading, overriding, and virtual method invocation • Use the access modifiers protected and the default (package-friendly) • Describe the concepts of constructor and method overloading • Describe the complete object construction and initialization operation Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance How does the Java programming language support object inheritance? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Subclassing The Employee class is shown here. Employee +name : String = "" +salary : double +birthDate : Date public class Employee { public String name = ""; public double salary; public Date birthDate; +getDetails() : String public String getDetails() {...} } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Subclassing The Manager class is shown here. Manager +name : String = "" +salary : double +birthDate : Date +department : String public class Manager { public String name = ""; public double salary; public Date birthDate; public String department; +getDetails() : String public String getDetails() {...} } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Class Diagrams for Employee and Manager Using Inheritance Employee +name : String = "" +salary : double +birthDate : Date public class Employee { public String name = ""; public double salary; public Date birthDate; +getDetails() : String public String getDetails() {...} } Manager +department : String public class Manager extends Employee { public String department; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Single Inheritance • When a class inherits from only one class, it is called single inheritance. • Interfaces provide the benefits of multiple inheritance without drawbacks. • Syntax of a Java class is as follows: class [extends ] { * } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Single Inheritance Employee +name : String = "" +salary : double +birthDate : Date +getDetails() : String Engineer Manager Secretary +department : String = "" Director +carAllowance : double +increaseAllowance() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Access Control Access modifiers on class member declarations are listed here. Modifier Same Class Same Package Subclass Universe private Yes default Yes Yes protected Yes Yes Yes public Yes Yes Yes Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Overriding Methods • A subclass can modify behavior inherited from a parent class. • A subclass can create a method with different functionality than the parent’s method but with the same: • Name • Return type1 • Argument list 1. In J2SE version 5, the return type can be a subclass of the overridden return type. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Overriding Methods 1 2 3 4 5 6 7 8 9 10 public class Employee { protected String name; protected double salary; protected Date birthDate; 1 2 3 4 5 6 7 8 9 public class Manager extends Employee { protected String department; public String getDetails() { return “Name: “ + name + “\n” + “Salary: “ + salary; } } public String getDetails() { return “Name: “ + name + “\n” + “Salary: “ + salary + "\n" + “Manager of: “ + department; } } Java™ Programming Language Copyright 2005 Sun Microsystems
Sun Services Overridden Methods Cannot Be Less Accessible 1 2 3 public class Parent { public void doSomething() {} } 1 2 3 public class Child extends Parent { private void doSomething() {} // illegal } 1 2 3 4 5 6 7 8 public class UseBoth { public void doOtherThing() { Parent p1 = new Parent(); Parent p2 = new Child(); p1.doSomething(); p2.doSomething(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Invoking Overridden Methods A subclass method may invoke a superclass method using the super keyword: • The keyword super is used in a class to refer to its superclass. • The keyword super is used to refer to the members of superclass, both data attributes and methods. • Behavior invoked does not have to be in the superclass; it can be further up in the hierarchy. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Invoking Overridden Methods 1 2 3 4 5 6 7 8 9 public class Employee { private String name; private double salary; private Date birthDate; 1 2 3 4 5 6 7 8 9 public class Manager extends Employee { private String department; public String getDetails() { return "Name: " + name + "\nSalary: " + salary; } } public String getDetails() { // call parent method return super.getDetails() + “\nDepartment: " + department; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Polymorphism • Polymorphism is the ability to have many different forms; for example, the Manager class has access to methods from Employee class. • An object has only one form. • A reference variable can refer to objects of different forms. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Polymorphism Employee e = new Manager(); // legal // illegal attempt to assign Manager attribute e.department = "Sales"; // the variable is declared as an Employee type, // even though the Manager object has that attribute Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Virtual Method Invocation • Virtual method invocation is performed as follows: Employee e = new Manager(); e.getDetails(); • Compile-time type and runtime type invocations have the following characteristics: • The method name must be a member of the declared variable type; in this case Employee has a method called getDetails. • The method implementation used is based on the runtime object’s type; in this case the Manager class has an implementation of the getDetails method.
Sun Services Heterogeneous Collections • Collections of objects with the same class type are called homogeneous collections. For example: MyDate[] dates = new MyDate[2]; dates[0] = new MyDate(22, 12, 1964); dates[1] = new MyDate(22, 7, 1964); • Collections of objects with different class types are called heterogeneous collections.
Sun Services Polymorphic Arguments Because a Manager is an Employee, the following is valid: public class TaxService { public TaxRate findTaxRate(Employee e) { // calculate the employee’s tax rate } } // Meanwhile, elsewhere in the application class TaxService taxSvc = new TaxService(); Manager m = new Manager(); TaxRate t = taxSvc.findTaxRate(m); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The instanceof Operator public class Employee extends Object public class Manager extends Employee public class Engineer extends Employee ---------------------------------------public void doSomething(Employee e) { if ( e instanceof Manager ) { // Process a Manager } else if ( e instanceof Engineer ) { // Process an Engineer } else { // Process any other type of Employee } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Casting Objects public void doSomething(Employee e) { if ( e instanceof Manager ) { Manager m = (Manager) e; System.out.println(“This is the manager of ” + m.getDepartment()); } // rest of operation } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Casting Objects • Use instanceof to test the type of an object. • Restore full functionality of an object by casting. • Check for proper casting using the following guidelines: • Casts upward in the hierarchy are done implicitly. • Downward casts must be to a subclass and checked by the compiler. • The object type is checked at runtime when runtime errors can occur. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Overloading Methods • Use overloading as follows: public void println(int i) public void println(float f) public void println(String s) • Argument lists must differ. • Return types can be different. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Methods Using Variable Arguments • Methods using variable arguments permit multiple number of arguments in methods. For example: public class Statistics { public float average(int... nums) { int sum = 0; for ( int x : nums ) { sum += x; } return ((float) sum) / nums.length; } } • The vararg parameter is treated as an array. For example: float gradePointAverage = stats.average(4, 3, 4); float averageAge = stats.
Sun Services Overloading Constructors • As with methods, constructors can be overloaded. An example is: public Employee(String name, double salary, Date DoB) public Employee(String name, double salary) public Employee(String name, Date DoB) • Argument lists must differ. • You can use the this reference at the first line of a constructor to call another constructor. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Overloading Constructors 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 public class Employee { private static final double BASE_SALARY = 15000.00; private String name; private double salary; private Date birthDate; public Employee(String name, double salary, Date DoB) { this.name = name; this.salary = salary; this.
Sun Services Constructors Are Not Inherited • A subclass inherits all methods and variables from the superclass (parent class). • A subclass does not inherit the constructor from the superclass. • Two ways to include a constructor are: • Use the default constructor. • Write one or more explicit constructors. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Invoking Parent Class Constructors • To invoke a parent constructor, you must place a call to super in the first line of the constructor. • You can call a specific parent constructor by the arguments that you use in the call to super. • If no this or super call is used in a constructor, then the compiler adds an implicit call to super() that calls the parent no argument constructor (which could be the default constructor).
Sun Services Invoking Parent Class Constructors 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 public class Manager extends Employee { private String department; public Manager(String name, double salary, String dept) { super(name, salary); department = dept; } public Manager(String name, String dept) { super(name); department = dept; } public Manager(String dept) { // This code fails: no super() department = dept; } //more Manager code... } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Constructing and Initializing Objects: A Slight Reprise Memory is allocated and default initialization occurs. Instance variable initialization uses these steps recursively: 1. Bind constructor parameters. 2. If explicit this(), call recursively, and then skip to Step 5. 3. Call recursively the implicit or explicit super call, except for Object. 4. Execute the explicit instance variable initializers. 5. Execute the body of the current constructor.
} Sun Services Constructor and Initialization Examples 1 2 3 } public class Object { public Object() {} 1 2 3 4 5 6 7 8 9 10 11 12 13 14 } } Module 6, slide 31 of 43 public Manager(String n, String d) { super(n); department = d; public class Manager extends Employee { private String department; } public Employee(String n, Date DoB) { // implicit super(); name = n; birthDate = DoB; } public Employee(String n) { this(n, null); public class Employee extends Object { private String name; private do
Sun Services Constructor and Initialization Examples 0 Basic initialization 0.1 Allocate memory for the complete Manager object 0.2 Initialize all instance variables to their default values (0 or null) 1 Call constructor: Manager("Joe Smith", "Sales") 1.1 Bind constructor parameters: n="Joe Smith", d="Sales" 1.2 No explicit this() call 1.3 Call super(n) for Employee(String) 1.3.1 Bind constructor parameters: n="Joe Smith" 1.3.2 Call this(n, null) for Employee(String, Date) 1.3.2.
Sun Services Constructor and Initialization Examples 1.3.2.4 Initialize explicit Employee variables: salary=15000.00; 1.3.2.5 Execute body: name="Joe Smith"; date=null; 1.3.3 - 1.3.4 Steps skipped 1.3.5 Execute body: No body in Employee(String) 1.4 No explicit initializers for Manager 1.5 Execute body: department="Sales" Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Object Class • The Object class is the root of all classes in Java. • A class declaration with no extends clause implies extends Object. For example: public class Employee { ... } is equivalent to: public class Employee extends Object { ... } • Two important methods are: • equals • toString Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The equals Method • The == operator determines if two references are identical to each other (that is, refer to the same object). • The equals method determines if objects are equal but not necessarily identical. • The Object implementation of the equals method uses the == operator. • User classes can override the equals method to implement a domain-specific test for equality. • Note: You should override the hashCode method if you override the equals method.
Sun Services An equals Example 1 2 3 4 5 6 7 8 9 10 public class MyDate { private int day; private int month; private int year; public MyDate(int day, int month, int year) { this.day = day; this.month = month; this.year = year; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services An equals Example 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 public boolean equals(Object o) { boolean result = false; if ( (o != null) && (o instanceof MyDate) ) { MyDate d = (MyDate) o; if ( (day == d.day) && (month == d.month) && (year == d.year) ) { result = true; } } return result; } public int hashCode() { return (day ^ month ^ year); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services An equals Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 class TestEquals { public static void main(String[] args) { MyDate date1 = new MyDate(14, 3, 1976); MyDate date2 = new MyDate(14, 3, 1976); if ( date1 == date2 ) { System.out.println("date1 is identical to date2"); } else { System.out.println("date1 is not identical to date2"); } if ( date1.equals(date2) ) { System.out.println("date1 is equal to date2"); } else { System.out.
Sun Services An equals Example 17 18 19 20 21 22 23 24 25 26 27 System.out.println("set date2 = date1;"); date2 = date1; if ( date1 == date2 ) { System.out.println("date1 is identical to date2"); } else { System.out.println("date1 is not identical to date2"); } } } This example generates the following output: date1 is not identical to date2 date1 is equal to date2 set date2 = date1; date1 is identical to date2 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The toString Method The toString method has the following characteristics: • This method converts an object to a String. • Use this method during string concatenation. • Override this method to provide information about a user-defined object in readable format. • Use the wrapper class’s toString static method to convert primitive types to a String. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Wrapper Classes Look at primitive data elements as objects. Primitive Data Type Wrapper Class boolean Boolean byte Byte char Character short Short int Integer long Long float Float double Double Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Wrapper Classes An example of a wrapper class is: int pInt = 420; Integer wInt = new Integer(pInt); // this is called boxing int p2 = wInt.intValue(); // this is called unboxing Other methods are: int x = Integer.valueOf(str).intValue(); int x = Integer.parseInt(str); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Autoboxing of Primitive Types Autoboxing has the following description: • Conversion of primitive types to the object equivalent • Wrapper classes not always needed • Example: int pInt = 420; Integer wInt = pInt; // this is called autoboxing int p2 = wInt; // this is called autounboxing • Language feature used most often when dealing with collections • Wrapped primitives also usable in arithmetic expressions • Performance loss when using autoboxing Java™ Programming Language Copyright 2005 Su
Sun Services Module 7 Advanced Class Features Java™ Programming Language
Sun Services Objectives • • • • • • Create static variables, methods, and initializers Create final classes, methods, and variables Create and use enumerated types Use the static import statement Create abstract classes and methods Create and use an interface Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance • How can you create a constant? • How can you declare data that is shared by all instances of a given class? • How can you keep a class or method from being subclassed or overridden? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The static Keyword • The static keyword is used as a modifier on variables, methods, and nested classes. • The static keyword declares the attribute or method is associated with the class as a whole rather than any particular instance of that class. • Thus static members are often called class members, such as class attributes or class methods. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Class Attributes Class attributes are shared among all instances of a class: Count +counter : int = 0 -serialNumber : int «instanceOf» 1 2 3 4 5 6 7 8 9 «instanceOf» c1 : Count c2 : Count serialNumber=1 serialNumber=2 public class Count { private int serialNumber; public static int counter = 0; public Count() { counter++; serialNumber = counter; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Class Attributes If the static member is public: 1 2 3 4 5 6 7 8 public class Count1 { private int serialNumber; public static int counter = 0; public Count1() { counter++; serialNumber = counter; } } it can be accessed from outside the class without an instance: 1 2 3 4 5 public class OtherClass { public void incrementNumber() { Count1.counter++; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Class Methods You can create static methods: 1 2 3 4 5 6 7 8 9 10 11 12 13 public class Count2 { private int serialNumber; private static int counter = 0; public static int getTotalCount() { return counter; } public Count2() { counter++; serialNumber = counter; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Class Methods You can invoke static methods without any instance of the class to which it belongs: 1 2 3 4 5 6 7 8 9 public class TestCounter { public static void main(String[] args) { System.out.println("Number of counter is " + Count2.getTotalCount()); Count2 counter = new Count2(); System.out.println("Number of counter is " + Count2.
Sun Services Class Methods Static methods cannot access instance variables: 1 2 3 4 5 6 7 8 public class Count3 { private int serialNumber; private static int counter = 0; public static int getSerialNumber() { return serialNumber; // COMPILER ERROR! } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Static Initializers • A class can contain code in a static block that does not exist within a method body. • Static block code executes once only, when the class is loaded. • Usually, a static block is used to initialize static (class) attributes. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Static Initializers 1 2 3 4 5 6 public class Count4 { public static int counter; static { counter = Integer.getInteger("myApp.Count4.counter").intValue(); } } 1 2 3 4 5 public class TestStaticInit { public static void main(String[] args) { System.out.println("counter = "+ Count4.counter); } } The output of the TestStaticInit program is: java -DmyApp.Count4.counter=47 TestStaticInit counter = 47 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The final Keyword • • • • You cannot subclass a final class. You cannot override a final method. A final variable is a constant. You can set a final variable once only, but that assignment can occur independently of the declaration; this is called a blank final variable. • A blank final instance attribute must be set in every constructor. • A blank final method variable must be set in the method body before being used. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Final Variables Constants are static final variables. public class Bank { private static final double ... // more declarations } DEFAULT_INTEREST_RATE = 3.2; Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Blank Final Variables 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 public class Customer { private final long customerID; public Customer() { customerID = createID(); } public long getID() { return customerID; } private long createID() { return ... // generate new ID } // more declarations } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Old-Style Enumerated Type Idiom Enumerated types are a common idiom in programming. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 package cards.domain; public class PlayingCard { // pseudo enumerated type public static final int SUIT_SPADES public static final int SUIT_HEARTS public static final int SUIT_CLUBS public static final int SUIT_DIAMONDS = = = = 0; 1; 2; 3; private int suit; private int rank; public PlayingCard(int suit, int rank) { this.suit = suit; this.
Sun Services Old-Style Enumerated Type Idiom 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 public String getSuitName() { String name = ““; switch ( suit ) { case SUIT_SPADES: name = “Spades”; break; case SUIT_HEARTS: name = “Hearts”; break; case SUIT_CLUBS: name = “Clubs”; break; case SUIT_DIAMONDS: name = “Diamonds”; break; default: System.err.println(“Invalid suit.”); } return name; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Old-Style Enumerated Type Idiom Old-style idiom is not type-safe: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 package cards.tests; import cards.domain.PlayingCard; public class TestPlayingCard { public static void main(String[] args) { PlayingCard card1 = new PlayingCard(PlayingCard.SUIT_SPADES, 2); System.out.println(“card1 is the “ + card1.getRank() + “ of “ + card1.getSuitName()); // You can create a playing card with a bogus suit. PlayingCard card2 = new PlayingCard(47, 2); System.out.
Sun Services Old-Style Enumerated Type Idiom This enumerated type idiom has several problems: • • • • Not type-safe No namespace Brittle character Uninformative printed values Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The New Enumerated Type Now you can create type-safe enumerated types: 0 1 2 3 4 5 6 7 8 package cards.domain; public enum Suit { SPADES, HEARTS, CLUBS, DIAMONDS } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The New Enumerated Type Using enumerated types is easy: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 package cards.domain; public class PlayingCard { private Suit suit; private int rank; public PlayingCard(Suit suit, int rank) { this.suit = suit; this.rank = rank; } public Suit getSuit() { return suit; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The New Enumerated Type 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 public String getSuitName() { String name = ““; switch ( suit ) { case SPADES: name = “Spades”; break; case HEARTS: name = “Hearts”; break; case CLUBS: name = “Clubs”; break; case DIAMONDS: name = “Diamonds”; break; default: // No need for error checking as the Suit // enum is finite. } return name; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The New Enumerated Type Enumerated types are type-safe: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 package cards.tests; import cards.domain.PlayingCard; import cards.domain.Suit; public class TestPlayingCard { public static void main(String[] args) { PlayingCard card1 = new PlayingCard(Suit.SPADES, 2); System.out.println(“card1 is the “ + card1.getRank() + “ of “ + card1.getSuitName()); // PlayingCard card2 = new PlayingCard(47, 2); // This will not compile.
Sun Services Advanced Enumerated Types Enumerated types can have attributes and methods: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 package cards.domain; public enum Suit { SPADES (“Spades”), HEARTS (“Hearts”), CLUBS (“Clubs”), DIAMONDS (“Diamonds”); private final String name; private Suit(String name) { this.name = name; } public String getName() { return name; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Advanced Enumerated Types Public methods on enumerated types are accessible: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 package cards.tests; import cards.domain.PlayingCard; import cards.domain.Suit; public class TestPlayingCard { public static void main(String[] args) { PlayingCard card1 = new PlayingCard(Suit.SPADES, 2); System.out.println(“card1 is the “ + card1.getRank() + “ of “ + card1.getSuit().getName()); // NewPlayingCard card2 = new NewPlayingCard(47, 2); // This will not compile.
Sun Services Static Imports • A static import imports the static members from a class: import static ..; OR import static ..*; • A static import imports members individually or collectively: import static cards.domain.Suit.SPADES; OR import static cards.domain.Suit.*; • There is no need to qualify the static constants: PlayingCard card1 = new PlayingCard(SPADES, 2); • Use this feature sparingly.
Sun Services Static Imports An 0example of a static import is: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 package cards.tests; import cards.domain.PlayingCard; import static cards.domain.Suit.*; public class TestPlayingCard { public static void main(String[] args) { PlayingCard card1 = new PlayingCard(SPADES, 2); System.out.println(“card1 is the “ + card1.getRank() + “ of “ + card1.getSuit().getName()); // NewPlayingCard card2 = new NewPlayingCard(47, 2); // This will not compile.
Sun Services Abstract Classes The design of the Shipping system looks like this: shipping ShippingMain «Uses» domain Company reports FuelNeedsReport «Uses» Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision F 0..
Sun Services Abstract Classes Fleet initialization code is shown here: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class ShippingMain { public static void main(String[] args) { Company c = new Company(); // populate the company with a fleet of vehicles c.addVehicle( new Truck(10000.0) ); c.addVehicle( new Truck(15000.0) ); c.addVehicle( new RiverBarge(500000.0) ); c.addVehicle( new Truck(9500.0) ); c.addVehicle( new RiverBarge(750000.0) ); FuelNeedsReport report = new FuelNeedsReport(c); report.
Sun Services Abstract Classes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class FuelNeedsReport { private Company company; public FuelNeedsReport(Company company) { this.company = company; } public void generateText(PrintStream output) { Vehicle1 v; double fuel; double total_fuel = 0.0; for ( int i = 0; i < company.getFleetSize(); i++ ) { v = company.getVehicle(i); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Abstract Classes 16 17 18 19 20 21 22 23 24 25 // Calculate the fuel needed for this trip fuel = v.calcTripDistance() / v.calcFuelEfficency(); output.println("Vehicle " + v.getName() + " needs " + fuel + " liters of fuel."); total_fuel += fuel; } output.println("Total fuel needs is " + total_fuel + " liters."); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Solution An abstract class models a class of objects in which the full implementation is not known but is supplied by the concrete subclasses.
Sun Services The Solution The declaration of the Vehicle class is: 1 2 3 4 public abstract class Vehicle { public abstract double calcFuelEfficiency(); public abstract double calcTripDistance(); } The Truck class must create an implementation: 1 2 3 4 5 6 7 8 9 public class Truck extends Vehicle { public Truck(double maxLoad) {...
Sun Services The Solution Likewise, the RiverBarge class must create an implementation: 1 2 3 4 5 6 7 8 9 public class RiverBarge extends Vehicle { public RiverBarge(double maxLoad) {...} public double calcFuelEfficiency() { /* calculate the fuel efficiency of a river barge */ } public double calcTripDistance() { /* calculate the distance of this trip along the river-ways */ } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Interfaces • A public interface is a contract between client code and the class that implements that interface. • A Java interface is a formal declaration of such a contract in which all methods contain no implementation. • Many unrelated classes can implement the same interface. • A class can implement many unrelated interfaces.
Sun Services The Flyer Example «interface» Flyer +takeOff() +land() +fly() Airplane +takeOff() +land() +fly() public interface Flyer { public void takeOff(); public void land(); public void fly(); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Flyer Example public class Airplane implements Flyer { public void takeOff() { // accelerate until lift-off // raise landing gear } public void land() { // lower landing gear // decelerate and lower flaps until touch-down // apply brakes } public void fly() { // keep those engines running } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Flyer Example «interface» Flyer +takeOff() +land() +fly() Airplane +takeOff() +land() +fly() Bird Superman +takeOff() +land() +fly() +buildNest() +layEggs() +takeOff() +land() +fly() +leapBuilding() +stopBullet() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Flyer Example Animal «interface» +eat() Flyer Vehicle +takeOff() +land() +fly() Kryptonian Airplane +takeOff() +land() +fly() Bird Superman +takeOff() +land() +fly() +buildNest() +layEggs() +eat() +takeOff() +land() +fly() +leapBuilding() +stopBullet() +eat() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Flyer Example public class Bird extends Animal implements Flyer { public void takeOff() { /* take-off implementation public void land() { /* landing implementation public void fly() { /* fly implementation public void buildNest() { /* nest building behavior public void layEggs() { /* egg laying behavior public void eat() { /* override eating behavior } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Flyer Example Animal «interface» +eat() Flyer +takeOff() +land() +fly() Vehicle Kryptonian Airplane +takeOff() +land() +fly() SeaPlane Bird Superman +takeOff() +land() +fly() +buildNest() +layEggs() +eat() +takeOff() +land() +fly() +leapBuilding() +stopBullet() +eat() Helicopter Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Flyer Example public class Airport { public static void main(String[] args) { Airport metropolisAirport = new Airport(); Helicopter copter = new Helicopter(); SeaPlane sPlane = new SeaPlane(); metropolisAirport.givePermissionToLand(copter); metropolisAirport.givePermissionToLand(sPlane); } private void givePermissionToLand(Flyer f) { f.land(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Multiple Interface Example «interface» Flyer +takeOff() +land() +fly() Vehicle RiverBarge «interface» Airplane +dock() +cruise() +takeOff() +land() +fly() Sailer +dock() +cruise() SeaPlane Helicopter +dock() +cruise() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Multiple Interface Example public class Harbor { public static void main(String[] args) { Harbor bostonHarbor = new Harbor(); RiverBarge barge = new RiverBarge(); SeaPlane sPlane = new SeaPlane(); bostonHarbor.givePermissionToDock(barge); bostonHarbor.givePermissionToDock(sPlane); } private void givePermissionToDock(Sailer s) { s.dock(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Uses of Interfaces Interface uses include the following: • Declaring methods that one or more classes are expected to implement • Determining an object’s programming interface without revealing the actual body of the class • Capturing similarities between unrelated classes without forcing a class relationship • Simulating multiple inheritance by declaring a class that implements several interfaces Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 8 Exceptions and Assertions Java™ Programming Language
Sun Services Objectives • • • • • • • Define exceptions Use try, catch, and finally statements Describe exception categories Identify common exceptions Develop programs to handle your own exceptions Use assertions Distinguish appropriate and inappropriate uses of assertions • Enable assertions at runtime Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance • In most programming languages, how do you resolve runtime errors? • If you make assumptions about the way your code works, and those assumptions are wrong, what might happen? • Is it always necessary or desirable to expend CPU power testing assertions in production programs? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Exceptions and Assertions • Exceptions handle unexpected situations – Illegal argument, network failure, or file not found • Assertions document and test programming assumptions – This can never be negative here • Assertion tests can be removed entirely from code at runtime, so the code is not slowed down at all. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Exceptions • Conditions that can readily occur in a correct program are checked exceptions. These are represented by the Exception class. • Severe problems that normally are treated as fatal or situations that probably reflect program bugs are unchecked exceptions. Fatal situations are represented by the Error class. Probable bugs are represented by the RuntimeException class. • The API documentation shows checked exceptions that can be thrown from a method.
Sun Services Exception Example 1 2 3 4 5 6 7 8 9 public class AddArguments { public static void main(String args[]) { int sum = 0; for ( String arg : args ) { sum += Integer.parseInt(arg); } System.out.println("Sum = " + sum); } } java AddArguments 1 2 3 4 Sum = 10 java AddArguments 1 two 3.0 4 Exception in thread "main" java.lang.NumberFormatException: For input string: "two" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48) at java.lang.Integer.parseInt(Integer.
Sun Services The try-catch Statement 1 2 3 4 5 6 7 8 9 10 11 12 13 14 public class AddArguments2 { public static void main(String args[]) { try { int sum = 0; for ( String arg : args ) { sum += Integer.parseInt(arg); } System.out.println("Sum = " + sum); } catch (NumberFormatException nfe) { System.err.println("One of the command-line " + "arguments is not an integer."); } } } java AddArguments2 1 two 3.0 4 One of the command-line arguments is not an integer.
Sun Services The try-catch Statement 1 2 3 4 5 6 7 8 9 10 11 12 13 14 public class AddArguments3 { public static void main(String args[]) { int sum = 0; for ( String arg : args ) { try { sum += Integer.parseInt(arg); } catch (NumberFormatException nfe) { System.err.println("[" + arg + "] is not an integer" + " and will not be included in the sum."); } } System.out.println("Sum = " + sum); } } java AddArguments3 1 two 3.0 4 [two] is not an integer and will not be included in the sum. [3.
Sun Services The try-catch Statement A try-catch statement can use multiple catch clauses: try { // code that might throw one or more exceptions } catch (MyException e1) { // code to execute if a MyException exception is thrown } catch (MyOtherException e2) { // code to execute if a MyOtherException exception is thrown } catch (Exception e3) { // code to execute if any other exception is thrown } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Call Stack Mechanism • If an exception is not handled in the current try-catch block, it is thrown to the caller of that method. • If the exception gets back to the main method and is not handled there, the program is terminated abnormally. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The finally Clause The finally clause defines a block of code that always executes. 1 2 3 4 5 6 7 8 try { startFaucet(); waterLawn(); } catch (BrokenPipeException e) { logProblem(e); } finally { stopFaucet(); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Exception Categories StackOverflowError VirtualMachineError OutOfMemoryError Error AssertionError Throwable ArithmeticException RuntimeException NullPointerException IllegalArgumentException Exception SQLException EOFException IOException FileNotFoundException Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Common Exceptions • • • • • NullPointerException FileNotFoundException NumberFormatException ArithmeticException SecurityException Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Handle or Declare Rule Use the handle or declare rule as follows: • Handle the exception by using the try-catch-finally block. • Declare that the code causes an exception by using the throws clause. void trouble() throws IOException { ... } void trouble() throws IOException, MyException { ... } Other Principles • You do not need to declare runtime exceptions or errors. • You can choose to handle runtime exceptions. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Method Overriding and Exceptions The overriding method can throw: • No exceptions • One or more of the exceptions thrown by the overridden method • One or more subclasses of the exceptions thrown by the overridden method The overriding method cannot throw: • Additional exceptions not thrown by the overridden method • Superclasses of the exceptions thrown by the overridden method Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Method Overriding and Exceptions 1 2 3 4 5 public class TestA { public void methodA() throws IOException { // do some file manipulation } } 1 2 3 4 5 public class TestB1 extends TestA { public void methodA() throws EOFException { // do some file manipulation } } 1 2 3 4 5 public class TestB2 extends TestA { public void methodA() throws Exception { // WRONG // do some file manipulation } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating Your Own Exceptions 1 2 3 4 5 6 7 8 9 10 11 12 public class ServerTimedOutException extends Exception { private int port; public ServerTimedOutException(String message, int port) { super(message); this.port = port; } public int getPort() { return port; } } Use the getMessage method, inherited from the Exception class, to get the reason for which the exception was made. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Handling a User-Defined Exception A method can throw a user-defined, checked exception: 1 2 3 4 5 6 7 8 9 10 11 12 public void connectMe(String serverName) throws ServerTimedOutException { boolean successful; int portToConnect = 80; successful = open(serverName, portToConnect); if ( ! successful ) { throw new ServerTimedOutException("Could not connect", portToConnect); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Handling a User-Defined Exception Another method can use a try-catch block to capture user-defined exceptions: 1 2 3 4 5 6 7 8 9 10 11 12 13 public void findServer() { try { connectMe(defaultServer); } catch (ServerTimedOutException e) { System.out.println("Server timed out, trying alternative"); try { connectMe(alternativeServer); } catch (ServerTimedOutException e1) { System.out.println("Error: " + e1.getMessage() + " connecting to port " + e1.
Sun Services Assertions • Syntax of an assertion is: assert ; assert : ; • If evaluates false, then an AssertionError is thrown. • The second argument is converted to a string and used as descriptive text in the AssertionError message. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Recommended Uses of Assertions Use assertions to document and verify the assumptions and internal logic of a single method: • Internal invariants • Control flow invariants • Postconditions and class invariants Inappropriate Uses of Assertions • Do not use assertions to check the parameters of a public method. • Do not use methods in the assertion check that can cause side-effects. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Internal Invariants The problem is: 1 2 3 4 5 if (x > 0) { // do this } else { // do that } The solution is: 1 2 3 4 5 6 if (x > 0) { // do this } else { assert ( x == 0 ); // do that, unless x is negative } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Control Flow Invariants For example: 1 2 3 4 5 6 7 8 9 10 11 12 switch (suit) { case Suit.CLUBS: // ... break; case Suit.DIAMONDS: // ... break; case Suit.HEARTS: // ... break; case Suit.SPADES: // ... break; default: assert false : "Unknown playing card suit"; break; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Postconditions and Class Invariants For example: 1 2 3 4 5 6 7 8 9 10 11 12 13 public Object pop() { int size = this.getElementCount(); if (size == 0) { throw new RuntimeException("Attempt to pop from empty stack"); } Object result = /* code to retrieve the popped element */ ; // test the postcondition assert (this.getElementCount() == size - 1); return result; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Controlling Runtime Evaluation of Assertions • If assertion checking is disabled, the code runs as fast as if the check was never there. • Assertion checks are disabled by default. Enable assertions with the following commands: java -enableassertions MyProgram or: java -ea MyProgram • Assertion checking can be controlled on class, package, and package hierarchy bases, see: docs/guide/language/assert.html Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 9 Text-Based Applications Java™ Programming Language
Sun Services Objectives • Write a program that uses command-line arguments and system properties • Write a program that reads from standard input • Describe the C-type formatted input and output • Write a program that can create, read, and write files • Describe the basic hierarchy of collections in the Java 2 Software Development Kit (Java 2 SDK) • Write a program that uses sets and lists • Write a program to iterate over a collection • Write a program that uses generic collections Java™ Programming Lang
Sun Services Relevance • It is often the case that certain elements of a program should not be hard-coded, such as file names or the name of a database. How can a program be coded to supply these elements at runtime? • Simple arrays are far too static for most collections (that is, a fixed number of elements).
Sun Services Command-Line Arguments • Any Java technology application can use command-line arguments. • These string arguments are placed on the command line to launch the Java interpreter, after the class name: java TestArgs arg1 arg2 "another arg" • Each command-line argument is placed in the args array that is passed to the static main method: public static void main(String[] args) Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Command-Line Arguments 1 2 3 4 5 6 7 public class TestArgs { public static void main(String[] args) { for ( int i = 0; i < args.length; i++ ) { System.out.println("args[" + i + "] is ’" + args[i] + "’"); } } } Example execution: java TestArgs arg1 arg2 "another arg" args[0] is ’arg1’ args[1] is ’arg2’ args[2] is ’another arg’ Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services System Properties • System properties are a feature that replaces the concept of environment variables (which are platform-specific). • The System.getProperties method returns a Properties object. • The getProperty method returns a String representing the value of the named property. • Use the -D option to include a new property. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Properties Class • The Properties class implements a mapping of names to values (a String to String map). • The propertyNames method returns an Enumeration of all property names. • The getProperty method returns a String representing the value of the named property. • You can also read and write a properties collection into a file using load and store. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Properties Class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 import java.util.Properties; import java.util.Enumeration; public class TestProperties { public static void main(String[] args) { Properties props = System.getProperties(); Enumeration propNames = props.propertyNames(); while ( propNames.hasMoreElements() ) { String propName = (String) propNames.nextElement(); String property = props.getProperty(propName); System.out.
Sun Services The Properties Class Here is an example test run of this program: java -DmyProp=theValue TestProperties Here is the (partial) output: property property property property property property property property property ’java.version’ is ’1.5.0-rc’ ’java.compiler’ is ’NONE’ ’path.separator’ is ’:’ ’file.separator’ is ’/’ ’user.home’ is ’/home/basham’ ’java.specification.vendor’ is ’Sun Microsystems Inc.’ ’user.language’ is ’en’ ’user.
Sun Services Console I/O • The variable System.out enables you to write to standard output. It is an object of type PrintStream. • The variable System.in enables you to read from standard input. It is an object of type InputStream. • The variable System.err enables you to write to standard error. It is an object of type PrintStream. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Writing to Standard Output • The println methods print the argument and a newline character (\n). • The print methods print the argument without a newline character. • The print and println methods are overloaded for most primitive types (boolean, char, int, long, float, and double) and for char[], Object, and String. • The print(Object) and println(Object) methods call the toString method on the argument. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Reading From Standard Input 1 2 3 4 5 6 7 8 9 10 11 12 13 import java.io.*; public class KeyboardInput { public static void main (String args[]) { String s; // Create a buffered reader to read // each line from the keyboard. InputStreamReader ir = new InputStreamReader(System.in); BufferedReader in = new BufferedReader(ir); System.out.println("Unix: Type ctrl-d to exit." + "\nWindows: Type ctrl-z to exit"); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Reading From Standard Input 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 try { // Read each input line and echo it to the screen. s = in.readLine(); while ( s != null ) { System.out.println("Read: " + s); s = in.readLine(); } // Close the buffered reader. in.close(); } catch (IOException e) { // Catch any IO exceptions. e.printStackTrace(); } } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Simple Formatted Output • You can use the formatting functionality as follows out.printf(“name count\n”); String s = String.format(“%s %5d%n”, user, total); • Common formatting codes are listed in this table. Code Description %s Formats the argument as a string, usually by calling the toString method on the object. %d %o %x Formats an integer, as a decimal, octal, or hexadecimal value. %f %g Formats a floating point number. The %g code uses scientific notation.
Sun Services Simple Formatted Input • The Scanner API provides a formatted input function. • A Scanner can be used with console input streams as well as file or network streams. • You can read console input as follows: 1 2 3 4 5 6 7 8 9 10 11 12 import java.io.*; import java.util.Scanner; public class ScanTest { public static void main(String [] args) { Scanner s = new Scanner(System.in); String param = s.next(); System.out.println("the param 1" + param); int value = s.nextInt(); System.out.
Sun Services Files and File I/O The java.io package enables you to do the following: • Create File objects • Manipulate File objects • Read and write to file streams Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating a New File Object The File class provides several utilities: • File myFile; • myFile = new File("myfile.txt"); • myFile = new File("MyDocs", "myfile.txt"); Directories are treated just like files in Java; the File class supports methods for retrieving an array of files in the directory, as follows: File myDir = new File("MyDocs"); myFile = new File(myDir, "myfile.txt"); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The File Tests and Utilities • File information: String getName() String getPath() String getAbsolutePath() String getParent() long lastModified() long length() • File modification: boolean renameTo(File newName) boolean delete() • Directory utilities: boolean mkdir() String[] list() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The File Tests and Utilities • File tests: boolean boolean boolean boolean boolean boolean exists() canWrite() canRead() isFile() isDirectory() isAbsolute(); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services File Stream I/O • For file input: • Use the FileReader class to read characters. • Use the BufferedReader class to use the readLine method. • For file output: • Use the FileWriter class to write characters. • Use the PrintWriter class to use the print and println methods. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services File Stream I/O A file input example is: 1 2 3 4 5 6 7 8 9 10 11 12 13 import java.io.*; public class ReadFile { public static void main (String[] args) { // Create file File file = new File(args[0]); try { // Create a buffered reader // to read each line from a file. BufferedReader in = new BufferedReader(new FileReader(file)); String s; Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services File Stream I/O 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 // Read each line from the file and echo it to the screen. s = in.readLine(); while ( s != null ) { System.out.println("Read: " + s); s = in.readLine(); } // Close the buffered reader in.close(); } catch (FileNotFoundException e1) { // If this file does not exist System.err.println("File not found: " + file); } catch (IOException e2) { // Catch any other IO exceptions. e2.
Sun Services File Output Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 import java.io.*; public class WriteFile { public static void main (String[] args) { // Create file File file = new File(args[0]); try { // Create a buffered reader to read each line from standard in. InputStreamReader isr = new InputStreamReader(System.in); BufferedReader in = new BufferedReader(isr); // Create a print writer on this file.
Sun Services File Output Example 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 System.out.print("Enter file text. "); System.out.println("[Type ctrl-d to stop.]"); // Read each input line and echo it to the screen. while ((s = in.readLine()) != null) { out.println(s); } // Close the buffered reader and the file print writer. in.close(); out.close(); } catch (IOException e) { // Catch any IO exceptions. e.printStackTrace(); } } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services The Collections API • A collection is a single object representing a group of objects known as its elements.
Sun Services The Collections API «interface» Collection +add(element : Object) : boolean +remove(element : Object) : boolean +size() : int +isEmpty() : boolean +contains(element : Object) : boolean +iterator() : Iterator «interface» «interface» Set List HashSet +add(index : int, element : Object) +remove(index : int) : Object +get(index : int) : Object +set(index : int, element Object) +indexOf(element : Object) : int +listIterator() : ListIterator ArrayList Java™ Programming Language Copyright 20
Sun Services A Set Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 import java.util.*; public class SetExample { public static void main(String[] args) { Set set = new HashSet(); set.add("one"); set.add("second"); set.add("3rd"); set.add(new Integer(4)); set.add(new Float(5.0F)); set.add("second"); // duplicate, not added set.add(new Integer(4)); // duplicate, not added System.out.println(set); } } The output generated from this program is: [one, second, 5.
Sun Services A List Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 import java.util.* public class ListExample { public static void main(String[] args) { List list = new ArrayList(); list.add("one"); list.add("second"); list.add("3rd"); list.add(new Integer(4)); list.add(new Float(5.0F)); list.add("second"); // duplicate, is added list.add(new Integer(4)); // duplicate, is added System.out.println(list); } } The output generated from this program is: [one, second, 3rd, 4, 5.
Sun Services Collections in JDK™ Version 1.1 Collections in the Java Development Kit (JDK™) include: • The class Vector implements the List interface. • The class Stack is a subclass of Vector and supports the push, pop, and peek methods. • The class Hashtable implements the Map interface. • The Enumeration interface is a variation on the Iterator interface. An enumeration is returned by the elements method in Vector, Stack, and Hashtable. • Classes are thread-safe, and therefore, heavy weight.
Sun Services Generics Generics are described as follows: • Provides compile-time type safety • Eliminates the need for casts Before Generics ArrayList list = new ArrayList(); list.add(0, new Integer(42)); int total = ((Integer)list.get(0)).intValue(); After Generics ArrayList list = new ArrayList(); list.add(0, new Integer(42)); int total = list.get(0).intValue(); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Generic Collections API «interface» Collection +add(element : E) : boolean +remove(element : E) : boolean +size() : int +isEmpty() : boolean +contains(element : E) : boolean +iterator() : Iterator «interface» «interface» Set List HashSet +add(index : int, element : E) +remove(index : int) : E +get(index : int) : E +set(index : int, element E) +indexOf(element : E) : int +listIterator() : ListIterator ArrayList Java™ Programming Language Copyright 2005 Sun Microsys
Sun Services Compiler Warnings 0 1 2 3 4 5 6 7 8 import java.util.*; public class GenericsWarning { public static void main(String[] args) { List list = new ArrayList(); list.add(0, new Integer(42)); int total = ((Integer)list.get(0)).intValue(); } } javac GenericsWarning.java Note: GenericsWarning.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. javac -Xlint:unchecked GenericsWarning.java GenericsWarning.
Sun Services Iterators • Iteration is the process of retrieving every element in a collection. • An Iterator of a Set is unordered. • A ListIterator of a List can be scanned forwards (using the next method) or backwards (using the previous method). List list = new ArrayList(); // add some elements Iterator elements = list.iterator(); while ( elements.hasNext() ) { System.out.println(elements.next()); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Iterator Interface Hierarchy «interface» Iterator +hasNext() : boolean +next() : E +remove() «interface» ListIterator +hasPrevious() : boolean +previous() : E +add(element : E) +set(element : E) Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Enhanced for Loop The enhanced for loop has the following characteristics: • • • • • Simplified iteration over collections Much shorter, clearer, and safer Effective for arrays Simpler when using nested loops Iterator disadvantages removed Iterators are error prone: • Iterator variables occur three times per loop. • This provides the opportunity for code to go wrong. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Enhanced for Loop An enhanced for loop can look like this: • Using iterators: public void deleteAll(Collection c){ for ( Iterator i = c.iterator() ; i.hasNext() ; ){ NameList nl = i.next(); nl.deleteItem(); } } • Using enhanced for loop in collections: public void deleteAll(Collection c){ for ( NameList nl : c ){ nl.deleteItem(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Enhanced for Loop • Using enhanced for loop in arrays: public int sum(int[] array){ int result = 0; for ( int element : array ) { result += element; } return result; } • Using enhanced for loop in nested loops: List subjects=...; List teachers=...; List courseList = new ArrayList(); for ( Subject subj : subjects ) { for ( Teacher tchr : teachers ) { courseList.add(new Course(subj, tchr)); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Module 10 Building Java GUIs Java™ Programming Language
Sun Services Objectives • Describe the Abstract Window Toolkit (AWT) package and its components • Define the terms containers, components, and layout managers, and describe how they work together to build a GUI • Use layout managers • Use the FlowLayout, BorderLayout, and GridLayout managers to achieve a desired dynamic layout • Add components to a container • Use the Frame and Panel containers appropriately • Describe how complex layouts with nested containers work Java™ Programming Language Copyright 200
Sun Services Relevance As a platform-independent programming language, how is Java technology used to make the graphical user interface (GUI) platform-independent? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Abstract Window Toolkit The AWT performs the following: • Provides GUI components that are used in all Java applets and applications • Contains classes that can be composed or extended; classes can also be abstract • Ensures that every GUI component that is displayed on the screen is a subclass of the abstract class Component or MenuComponent • Has Container, which is an abstract subclass of Component and includes two subclasses: • Panel • Window Java™ Programming Language Copyright 2005 Sun M
Sun Services The java.awt Package java.lang.Object Menu -- PopupMenu CheckboxMenuItem Dimension java.awt.geom.Dimension2D MenuBar MenuItem FileDialog Module 10, slide 5 of 37 Errors – AWTError Dialog Frame Applet (java.applet package) TextArea TextField Panel Window ScrollPane java.lang.
Sun Services Containers • Add components with the add() method. • The two main types of containers are Window and Panel. • A Window is a free floating window on the display. • A Panel is a container of GUI components that must exist in the context of some other container, such as a window or applet. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Positioning Components • The position and size of a component in a container is determined by a layout manager. • You can control the size or position of components by disabling the layout manager. You must then use setLocation(), setSize(), or setBounds() on components to locate them in the container. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Frames Frames have the following characteristics: • Are a subclass of Window • Have title and resizing corners • Are invisible initially; use setVisible(true) to expose the frame • Have BorderLayout as the default layout manager • Use the setLayout method to change the default layout manager Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The FrameExample Class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 import java.awt.*; public class FrameExample { private Frame f; public FrameExample() { f = new Frame("Hello Out There!"); } public void launchFrame() { f.setSize(170,170); f.setBackground(Color.blue); f.setVisible(true); } public static void main(String args[]) { FrameExample guiWindow = new FrameExample(); guiWindow.launchFrame(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Example Frame Solaris OS Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Panels • Panels provide a space for components. • This enables subpanels to have their own layout manager. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The FrameWithPanel Class 1 2 3 4 5 6 7 8 9 10 import java.awt.*; public class FrameWithPanel { private Frame f; private Panel pan; public FrameWithPanel(String title) { f = new Frame(title); pan = new Panel(); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The FrameWithPanel Class 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 public void launchFrame() { f.setSize(200,200); f.setBackground(Color.blue); f.setLayout(null); // Use default layout pan.setSize(100,100); pan.setBackground(Color.yellow); f.add(pan); f.setVisible(true); } public static void main(String args[]) { FrameWithPanel guiWindow = new FrameWithPanel("Frame with Panel"); guiWindow.launchFrame(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Example Panel Solaris OS Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Layout Managers • • • • • FlowLayout BorderLayout GridLayout CardLayout GridBagLayout Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Default Layout Managers Component Container Panel Window Frame Dialog BorderLayout Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services A Simple FlowLayout Example 1 2 3 4 5 6 7 8 9 10 11 12 import java.awt.*; public class LayoutExample { private Frame f; private Button b1; private Button b2; public LayoutExample() { f = new Frame("GUI example"); b1 = new Button("Press Me"); b2 = new Button("Don’t press Me"); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services A Simple FlowLayout Example 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 public void launchFrame() { f.setLayout(new FlowLayout()); f.add(b1); f.add(b2); f.pack(); f.setVisible(true); } public static void main(String args[]) { LayoutExample guiWindow = new LayoutExample(); guiWindow.launchFrame(); } } // end of LayoutExample class Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Example of FlowLayout Solaris OS Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The FlowLayout Manager The FlowLayout manager has the following characteristics: • • • • • Forms the default layout for the Panel class Adds components from left to right Alignment default is centered Uses components’ preferred sizes Uses the constructor to tune behavior Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The FlowLayout Resizing After user or program resizes Solaris OS Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The FlowExample Class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import java.awt.*; public class FlowExample { private Frame f; private Button button1; private Button button2; private Button button3; public FlowExample() { f = new Frame("Flow Layout"); button1 = new Button("Ok"); button2 = new Button("Open"); button3 = new Button("Close"); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The FlowExample Class 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 public void launchFrame() { f.setLayout(new FlowLayout()); f.add(button1); f.add(button2); f.add(button3); f.setSize(100,100); f.setVisible(true); } public static void main(String args[]) { FlowExample guiWindow = new FlowExample(); guiWindow.launchFrame(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The BorderLayout Manager • The BorderLayout manager is the default layout for the Frame class. • Components are added to specific regions. • The resizing behavior is as follows: • North, South, and Center regions adjust horizontally • East, West, and Center regions adjust vertically Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Organization of the Border Layout Components Center East West North South Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The BorderExample Class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import java.awt.*; public class BorderExample { private Frame f; private Button bn, bs, bw, be, bc; public BorderExample() { f = new Frame("Border Layout"); bn = new Button("B1"); bs = new Button("B2"); bw = new Button("B3"); be = new Button("B4"); bc = new Button("B5"); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The BorderExample Class 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 public void launchFrame() { f.add(bn, BorderLayout.NORTH); f.add(bs, BorderLayout.SOUTH); f.add(bw, BorderLayout.WEST); f.add(be, BorderLayout.EAST); f.add(bc, BorderLayout.CENTER); f.setSize(200,200); f.setVisible(true); } public static void main(String args[]) { BorderExample guiWindow2 = new BorderExample(); guiWindow2.launchFrame(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Example of BorderLayout After user or program resizes Solaris OS Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The GridLayout Manager • Components are added from left to right, and from top to bottom. • All regions are sized equally. • The constructor specifies the rows and columns. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The GridExample Class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 import java.awt.*; public class GridExample { private Frame f; private Button b1, b2, b3, b4, b5, b6; public GridExample() { f = new Frame("Grid Example"); b1 = new Button("1"); b2 = new Button("2"); b3 = new Button("3"); b4 = new Button("4"); b5 = new Button("5"); b6 = new Button("6"); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The GridExample Class 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 public void launchFrame() { f.setLayout (new GridLayout(3,2)); f.add(b1); f.add(b2); f.add(b3); f.add(b4); f.add(b5); f.add(b6); f.pack(); f.setVisible(true); } public static void main(String args[]) { GridExample grid = new GridExample(); grid.launchFrame(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Example of GridLayout After user or program resizes Solaris OS After user or program resizes Microsoft Windows Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The ComplexLayoutExample Class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 import java.awt.*; public class ComplexLayoutExample { private Frame f; private Panel p; private Button bw, bc; private Button bfile, bhelp; public ComplexLayoutExample() { f = new Frame("GUI example 3"); bw = new Button("West"); bc = new Button("Work space region"); bfile = new Button("File"); bhelp = new Button("Help"); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The ComplexLayoutExample Class 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 public void launchFrame() { // Add bw and bc buttons in the frame border f.add(bw, BorderLayout.WEST); f.add(bc, BorderLayout.CENTER); // Create panel for the buttons in the north border p = new Panel(); p.add(bfile); p.add(bhelp); f.add(p, BorderLayout.NORTH); // Pack the frame and make it visible f.pack(); f.
Sun Services Combining Layout Managers After user or program resizes Solaris OS Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Drawing in AWT • You can draw in any Component (although AWT provides the Canvas and Panel classes just for this purpose). • Typically, you create a subclass of Canvas or Panel and override the paint method. • The paint method is called every time the component is shown (for example, if another window overlapped the component and was then removed). • Every component has a Graphics object. • The Graphics class implements many drawing methods.
Sun Services Various Shapes Drawn by the Graphics Object Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 11 GUI Event Handling Java™ Programming Language
Sun Services Objectives • Define events and event handling • Write code to handle events that occur in a GUI • Describe the concept of adapter classes, including how and when to use them • Determine the user action that originated the event from the event object details • Identify the appropriate listener interface for a variety of event types • Create the appropriate event handler methods for a variety of event types • Understand the use of inner classes and anonymous classes in event handling Java™ Progr
Sun Services Relevance • What parts of a GUI are required to make it useful? • How does a graphical program handle a mouse click or any other type of user interaction? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services What Is an Event? • Events – Objects that describe what happened • Event sources – The generator of an event • Event handlers – A method that receives an event object, deciphers it, and processes the user’s interaction Frame Panel The user clicks on the button Button ActionEvent Some Event Handler actionPerformed(ActionEvent e) { ... } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Delegation Model • An event can be sent to many event handlers. Frame Panel The user clicks on the button One Event Handler Button ActionEvent actionPerformed(ActionEvent e) { ... } Another Event Handler actionPerformed(ActionEvent e) { ... } • Event handlers register with components when they are interested in events generated by that component. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Delegation Model • Client objects (handlers) register with a GUI component that they want to observe. • GUI components only trigger the handlers for the type of event that has occurred. • Most components can trigger more than one type of event. • The delegation model distributes the work among multiple classes. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services A Listener Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 import java.awt.*; public class TestButton { private Frame f; private Button b; public TestButton() { f = new Frame("Test"); b = new Button("Press Me!"); b.setActionCommand("ButtonPressed"); } public void launchFrame() { b.addActionListener(new ButtonHandler()); f.add(b,BorderLayout.CENTER); f.pack(); f.setVisible(true); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services A Listener Example 19 20 21 22 23 24 public static void main(String args[]) { TestButton guiApp = new TestButton(); guiApp.launchFrame(); } } Code for the event listener looks like this: 1 2 3 4 5 6 7 8 9 import java.awt.event.*; public class ButtonHandler implements ActionListener { public void actionPerformed(ActionEvent e) { System.out.println("Action occurred"); System.out.println("Button’s command is: " + e.
Sun Services Event Categories java.awt.AWTEvent java.util.EventObject java.awt.event ActionEvent FocusEvent AdjustmentEvent KeyEvent InputEvent ComponentEvent MouseEvent ContainerEvent ItemEvent WindowEvent TextEvent Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Method Categories and Interfaces Category Interface Name Methods Action ActionListener actionPerformed(ActionEvent) Item ItemListener itemStateChanged(ItemEvent) Mouse MouseListener mousePressed(MouseEvent) mouseReleased(MouseEvent) mouseEntered(MouseEvent) mouseExited(MouseEvent) mouseClicked(MouseEvent) Mouse motion MouseMotionListener mouseDragged(MouseEvent) mouseMoved(MouseEvent) Key KeyListener keyPressed(KeyEvent) keyReleased(KeyEvent) keyTyped(KeyEvent) Java™ Programm
Sun Services Method Categories and Interfaces Category Interface Name Methods Focus FocusListener focusGained(FocusEvent) focusLost(FocusEvent) Adjustment AdjustmentListener adjustmentValueChanged (AdjustmentEvent) Component ComponentListener componentMoved(ComponentEvent) componentHidden(ComponentEvent) componentResized(ComponentEvent) componentShown(ComponentEvent) Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Method Categories and Interfaces Category Interface Name Methods Window WindowListener windowClosing(WindowEvent) windowOpened(WindowEvent) windowIconified(WindowEvent) windowDeiconified(WindowEvent) windowClosed(WindowEvent) windowActivated(WindowEvent) windowDeactivated(WindowEvent) Container ContainerListener componentAdded(ContainerEvent) componentRemoved(ContainerEvent) Text TextListener textValueChanged(TextEvent) Java™ Programming Language Copyright 2005 Sun Microsystems, In
Sun Services Complex Example 1 2 3 4 5 6 7 8 9 10 11 12 import java.awt.*; import java.awt.event.*; public class TwoListener implements MouseMotionListener, MouseListener { private Frame f; private TextField tf; public TwoListener() { f = new Frame("Two listeners example"); tf = new TextField(30); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Complex Example 13 14 15 16 17 18 19 20 21 22 23 24 25 public void launchFrame() { Label label = new Label("Click and drag the mouse"); // Add components to the frame f.add(label, BorderLayout.NORTH); f.add(tf, BorderLayout.SOUTH); // Add this object as a listener f.addMouseMotionListener(this); f.addMouseListener(this); // Size the frame and make it visible f.setSize(300, 200); f.setVisible(true); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Complex Example 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 // These are MouseMotionListener events public void mouseDragged(MouseEvent e) { String s = "Mouse dragging: X = " + e.getX() + " Y = " + e.getY(); tf.setText(s); } public void mouseEntered(MouseEvent e) { String s = "The mouse entered"; tf.setText(s); } public void mouseExited(MouseEvent e) { String s = "The mouse has left the building"; tf.setText(s); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Complex Example 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 // Unused MouseMotionListener method. // All methods of a listener must be present in the // class even if they are not used. public void mouseMoved(MouseEvent e) { } // Unused MouseListener methods. public void mousePressed(MouseEvent e) { } public void mouseClicked(MouseEvent e) { } public void mouseReleased(MouseEvent e) { } public static void main(String args[]) { TwoListener two = new TwoListener(); two.
Sun Services Multiple Listeners • Multiple listeners cause unrelated parts of a program to react to the same event. • The handlers of all registered listeners are called when the event occurs. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Event Adapters • The listener classes that you define can extend adapter classes and override only the methods that you need. • An example is: 1 2 3 4 5 6 7 8 9 10 11 12 13 import java.awt.*; import java.awt.event.*; public class MouseClickHandler extends MouseAdapter { // We just need the mouseClick handler, so we use // an adapter to avoid having to write all the // event handler methods public void mouseClicked(MouseEvent e) { // Do stuff with the mouse click...
Sun Services Event Handling Using Inner Classes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 import java.awt.*; import java.awt.event.*; public class TestInner { private Frame f; private TextField tf; // used by inner class public TestInner() { f = new Frame("Inner classes example"); tf = new TextField(30); } class MyMouseMotionListener extends MouseMotionAdapter { public void mouseDragged(MouseEvent e) { String s = "Mouse dragging: X = "+ e.getX() + " Y = " + e.getY(); tf.
Sun Services Event Handling Using Inner Classes 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 public void launchFrame() { Label label = new Label("Click and drag the mouse"); // Add components to the frame f.add(label, BorderLayout.NORTH); f.add(tf, BorderLayout.SOUTH); // Add a listener that uses an Inner class f.addMouseMotionListener(new MyMouseMotionListener()); f.addMouseListener(new MouseClickHandler()); // Size the frame and make it visible f.setSize(300, 200); f.
Sun Services Event Handling Using Anonymous Classes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 import java.awt.*; import java.awt.event.*; public class TestAnonymous { private Frame f; private TextField tf; public TestAnonymous() { f = new Frame("Anonymous classes example"); tf = new TextField(30); } public static void main(String args[]) { TestAnonymous obj = new TestAnonymous(); obj.launchFrame(); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Event Handling Using Anonymous Classes 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 public void launchFrame() { Label label = new Label("Click and drag the mouse"); // Add components to the frame f.add(label, BorderLayout.NORTH); f.add(tf, BorderLayout.SOUTH); // Add a listener that uses an anonymous class f.addMouseMotionListener(new MouseMotionAdapter() { public void mouseDragged(MouseEvent e) { String s = "Mouse dragging: X = "+ e.getX() + " Y = " + e.getY(); tf.
Sun Services Module 12 GUI-Based Applications Java™ Programming Language
Sun Services Objectives • Identify the key AWT components and the events that they trigger • Describe how to construct a menu bar, menu, and menu items in a Java GUI • Understand how to change the color and font of a component Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance • You now know how to set up a Java GUI for both graphic output and interactive user input. However, only a few of the components from which GUIs can be built have been described. What other components would be useful in a GUI? • How can you create a menu for your GUI frame? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services AWT Components Component Type Description Button A named rectangular box used for receiving mouse clicks Canvas A panel used for drawing Checkbox A component enabling the user to select an item CheckboxMenuItem A checkbox within a menu Choice A pull-down static list of items Component The parent of all AWT components, except menu components Container The parent of all AWT containers Dialog A top-level window with a title and a border; dialogs can be modeless or modal Frame T
Sun Services AWT Components Component Type Description Label A text string component List A component that contains a dynamic set of items Menu An element under the menu bar, which contains a set of menu items MenuItem An item within a menu Panel A basic container class used most often to create complex layouts Scrollbar A component that enables a user to select from a range of values ScrollPane A container class that implements automatic horizontal and vertical scrolling for a single child
Sun Services AWT Components Component Type Description TextArea A component that enables the user to enter a block of text TextField A component that enables the user to enter a single line of text Window The base class of all GUI windows, without window manager controls Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services AWT Listeners Component Act Adj Cmp Cnt Foc Itm Key Mou MM Text Win Type ✓ ✓ ✓ ✓ ✓ Canvas ✓ ✓ ✓ ✓ ✓ Checkbox ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Button ✓ ✓ ✓ CheckboxMenuItem Choice ✓ ✓ Component ✓ ✓ ✓ ✓ ✓ Container ✓ ✓ ✓ ✓ ✓ ✓ Dialog ✓ ✓ ✓ ✓ ✓ ✓ Frame ✓ ✓ ✓ ✓ ✓ ✓ Label ✓ ✓ ✓ ✓ ✓ Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services AWT Listeners Component Act Adj Cmp Cnt Foc Itm Key Mou MM Text Win Type List ✓ MenuItem ✓ ✓ ✓ Panel ✓ Scrollbar ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ScrollPane ✓ TextArea ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ TextField ✓ Window ✓ ✓ ✓ ✓ Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services How to Create a Menu 1. Create a MenuBar object, and set it into a menu container, such as a Frame. 2. Create one or more Menu objects, and add them to the menu bar object. 3. Create one or more MenuItem objects, and add them to the menu object. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating a MenuBar 1 2 3 Frame f = new Frame("MenuBar"); MenuBar mb = new MenuBar(); f.setMenuBar(mb); Solaris OS Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating a Menu 1 2 3 4 5 6 7 8 9 Frame f = new Frame("Menu"); MenuBar mb = new MenuBar(); Menu m1 = new Menu("File"); Menu m2 = new Menu("Edit"); Menu m3 = new Menu("Help"); mb.add(m1); mb.add(m2); mb.setHelpMenu(m3); f.setMenuBar(mb); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating a Menu Solaris OS Microsoft Windows Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating a MenuItem 1 2 3 4 5 6 7 8 9 10 11 12 13 MenuItem mi1 = new MenuItem("New"); MenuItem mi2 = new MenuItem("Save"); MenuItem mi3 = new MenuItem("Load"); MenuItem mi4 = new MenuItem("Quit"); mi1.addActionListener(this); mi2.addActionListener(this); mi3.addActionListener(this); mi4.addActionListener(this); m1.add(mi1); m1.add(mi2); m1.add(mi3); m1.addSeparator(); m1.add(mi4); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating a MenuItem Solaris OS Microsoft Windows Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating a CheckBoxMenuItem 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 MenuBar mb = new MenuBar(); Menu m1 = new Menu("File"); Menu m2 = new Menu("Edit"); Menu m3 = new Menu("Help"); mb.add(m1); mb.add(m2); mb.setHelpMenu(m3); f.setMenuBar(mb); ..... MenuItem mi2 = new MenuItem("Save"); mi2.addActionListener(this); m1.add(mi2); ...... CheckboxMenuItem mi5 = new CheckboxMenuItem("Persistent"); mi5.addItemListener(this); m1.add(mi5); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services Creating a CheckBoxMenuItem Solaris OS Microsoft Windows Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Controlling Visual Aspects Commands to control visual aspects of the GUI include: • Colors: setForeground() setBackground() • Example: Color purple = new Color(255, 0, 255); Button b = new Button(“Purple”); b.setBackground(purple); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services J.F.C./Swing Technology • Java Foundation Class/Swing (J.F.C./Swing) technology is a second-generation GUI toolkit. • It builds on top of AWT, but supplants the components with lightweight versions. • There are many more components, and much more complex components, including JTable, JTree, and JComboBox. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 13 Threads Java™ Programming Language
Sun Services Objectives • Define a thread • Create separate threads in a Java technology program, controlling the code and data that are used by that thread • Control the execution of a thread and write platformindependent code with threads • Describe the difficulties that might arise when multiple threads share data • Use wait and notify to communicate between threads • Use synchronized to protect data from corruption Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance How do you get programs to perform multiple tasks concurrently? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Threads • What are threads? Threads are a virtual CPU. • The three parts of at thread are: • CPU • Code • Data CPU A thread or execution context Code Data Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating the Thread 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 public class ThreadTester { public static void main(String args[]) { HelloRunner r = new HelloRunner(); Thread t = new Thread(r); t.start(); } } class HelloRunner implements Runnable { int i; public void run() { i = 0; while (true) { System.out.println("Hello " + i++); if ( i == 50 ) { break; } } } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Creating the Thread • Multithreaded programming has these characteristics: • Multiple threads are from one Runnable instance. • Threads share the same data and code. • For example: Thread t1 = new Thread(r); Thread t2 = new Thread(r); } New Thread Thread t CPU HelloRunner Code Data Class Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Starting the Thread • Use the start method. • Place the thread in a runnable state. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Thread Scheduling Blocked New Dead Unblocked Event Blocked start() Runnable Scheduler Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Thread Scheduling Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class Runner implements Runnable { public void run() { while (true) { // do lots of interesting stuff // ... // Give other threads a chance try { Thread.sleep(10); } catch (InterruptedException e) { // This thread’s sleep was interrupted // by another thread } } } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Terminating a Thread 1 2 3 4 5 6 7 8 9 10 11 12 13 14 public class Runner implements Runnable { private boolean timeToQuit=false; public void run() { while ( ! timeToQuit ) { // continue doing work } // clean up before run() ends } public void stopRunning() { timeToQuit=true; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Terminating a Thread 1 2 3 4 5 6 7 8 9 10 11 12 13 public class ThreadController { private Runner r = new Runner(); private Thread t = new Thread(r); public void startThread() { t.start(); } public void stopThread() { // use specific instance of Runner r.stopRunning(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Basic Control of Threads • Test threads: isAlive() • Access thread priority: getPriority() setPriority() • Put threads on hold: Thread.sleep() join() Thread.yield() // static method // static method Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The join Method 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 public static void main(String[] args) { Thread t = new Thread(new Runner()); t.start(); ... // Do stuff in parallel with the other thread for a while ... // Wait here for the other thread to finish try { t.join(); } catch (InterruptedException e) { // the other thread came back early } ... // Now continue in this thread ... } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Other Ways to Create Threads 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 public class MyThread extends Thread { public void run() { while ( true ) { // do lots of interesting stuff try { Thread.sleep(100); } catch (InterruptedException e) { // sleep interrupted } } } public static void main(String args[]) { Thread t = new MyThread(); t.start(); } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Selecting a Way to Create Threads • Implement Runnable: • Better object-oriented design • Single inheritance • Consistency • Extend Thread: Simpler code Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Using the synchronized Keyword 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class MyStack { int idx = 0; char [] data = new char[6]; public void push(char c) { data[idx] = c; idx++; } public char pop() { idx--; return data[idx]; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Object Lock Flag • Every object has a flag that is a type of lock flag. • The synchronized enables interaction with the lock flag. Object this Code or Behavior Data or State Thread before synchronized(this) public void push(char c) { synchronized (this) { data[idx] = c; idx++; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Object Lock Flag Object this Code or Behavior Data or State Thread after synchronized(this) public void push(char c) { synchronized (this) { data[idx] = c; idx++; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Object Lock Flag Object this lock flag missing Code or Behavior Data or State Another thread, trying to execute synchronized(this) Waiting for public char pop() { synchronized (this) { object lock idx--; return data[idx]; } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Releasing the Lock Flag The lock flag is released in the following events: • Released when the thread passes the end of the synchronized code block • Released automatically when a break, return, or exception is thrown by the synchronized code block Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Using synchronized – Putting It Together • All access to delicate data should be synchronized. • Delicate data protected by synchronized should be private. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Using synchronized – Putting It Together The following two code segments are equivalent: public void push(char c) { synchronized(this) { // The push method code } } public synchronized void push(char c) { // The push method code } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Thread State Diagram With Synchronization Blocked New Dead Unblocked start() Runnable Event Blocked Scheduler Lock Acquired run() Completes Running Synchronized Blocked in Object’s Lock Pool Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Deadlock A deadlock has the following characteristics: • It is two threads, each waiting for a lock from the other. • It is not detected or avoided. • Deadlock can be avoided by: • Deciding on the order to obtain locks • Adhering to this order throughout • Releasing locks in reverse order Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Thread Interaction – wait and notify • Scenario: Consider yourself and a cab driver as two threads. • The problem: How do you determine when you are at your destination? • The solution: • You notify the cab driver of your destination and relax. • The driver drives and notifies you upon arrival at your destination. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Thread Interaction Thread interactions include: • The wait and notify methods • The pools: • Wait pool • Lock pool Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Thread State Diagram With wait and notify Blocked New Dead Unblocked start() Runnable Event Blocked Scheduler Lock Acquired run() Completes Running Synchronized Blocked in Object’s Lock Pool Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Monitor Model for Synchronization • Leave shared data in a consistent state. • Ensure programs cannot deadlock. • Do not put threads expecting different notifications in the same wait pool. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Producer Class 1 2 3 4 5 6 7 8 9 10 11 12 package mod13; public class Producer implements Runnable { private SyncStack theStack; private int num; private static int counter = 1; public Producer (SyncStack s) { theStack = s; num = counter++; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Producer Class 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 public void run() { char c; for (int i = 0; i < 200; i++) { c = (char)(Math.random() * 26 +’A’); theStack.push(c); System.out.println(“Producer” + num + “: “ + c); try { Thread.sleep((int)(Math.random() * 300)); } catch (InterruptedException e) { // ignore it } } } // END run method } // END Producer class Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Consumer Class 1 2 3 4 5 6 7 8 9 10 11 12 package mod13; public class Consumer implements Runnable { private SyncStack theStack; private int num; private static int counter = 1; public Consumer (SyncStack s) { theStack = s; num = counter++; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Consumer Class 13 14 15 16 17 18 19 20 21 22 23 24 25 26 public void run() { char c; for (int i = 0; i < 200; i++) { c = theStack.pop(); System.out.println(“Consumer” + num + “: “ + c); try { Thread.sleep((int)(Math.random() * 300)); } catch (InterruptedException e) { // ignore it } } } // END run method Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The SyncStack Class This is a sketch of the SyncStack class: public class SyncStack { private List buffer = new ArrayList(400); public synchronized char pop() { // pop code here } public synchronized void push(char c) { // push code here } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The pop Method 9 10 11 12 13 14 15 16 17 18 19 20 public synchronized char pop() { char c; while (buffer.size() == 0) { try { this.wait(); } catch (InterruptedException e) { // ignore it... } } c = buffer.remove(buffer.size()-1); return c; } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The push Method 22 23 24 25 public synchronized void push(char c) { this.notify(); buffer.add(c); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The SyncTest Class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 package mod13; public class SyncTest { public static void main(String[] args) { SyncStack stack = new SyncStack(); Producer p1 = new Producer(stack); Thread prodT1 = new Thread (p1); prodT1.start(); Producer p2 = new Producer(stack); Thread prodT2 = new Thread (p2); prodT2.start(); Consumer c1 = new Consumer(stack); Thread consT1 = new Thread (c1); consT1.
Sun Services The SyncTest Class Producer2: Consumer1: Producer2: Consumer2: Producer2: Producer1: Producer1: Consumer2: Consumer1: Producer2: Producer2: Consumer2: Consumer2: Producer1: Consumer1: Producer2: Consumer2: Consumer2: F F K K T N V V N V U U V F F M M T Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 14 Advanced I/O Streams Java™ Programming Language
Sun Services Objectives • Describe the main features of the java.io package • Construct node and processing streams, and use them appropriately • Distinguish readers and writers from streams, and select appropriately between them Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance • What mechanisms are in place within the Java programming language to read and write from sources (or sinks) other than files? • How are international character sets supported in I/O operations? • What are the possible sources and sinks of character and byte streams? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services I/O Fundamentals • A stream can be thought of as a flow of data from a source or to a sink. • A source stream initiates the flow of data, also called an input stream. • A sink stream terminates the flow of data, also called an output stream. • Sources and sinks are both node streams. • Types of node streams are files, memory, and pipes between threads or processes. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Fundamental Stream Classes Stream Byte Streams Character Streams Source streams InputStream Reader Sink streams OutputStream Writer Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Data Within Streams • Java technology supports two types of streams: character and byte. • Input and output of character data is handled by readers and writers. • Input and output of byte data is handled by input streams and output streams: • Normally, the term stream refers to a byte stream. • The terms reader and writer refer to character streams. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The InputStream Methods • The three basic read methods are: int read() int read(byte[] buffer) int read(byte[] buffer, int offset, int length) • Other methods include: void close() int available() long skip(long n) boolean markSupported() void mark(int readlimit) void reset() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The OutputStream Methods • The three basic write methods are: void write(int c) void write(byte[] buffer) void write(byte[] buffer, int offset, int length) • Other methods include: void close() void flush() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Reader Methods • The three basic read methods are: int read() int read(char[] cbuf) int read(char[] cbuf, int offset, int length) • Other methods include: void close() boolean ready() long skip(long n) boolean markSupported() void mark(int readAheadLimit) void reset() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Writer Methods • The basic write methods are: void void void void void write(int c) write(char[] write(char[] write(String write(String cbuf) cbuf, int offset, int length) string) string, int offset, int length) • Other methods include: void close() void flush() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Node Streams Type Character Streams Byte Streams File FileReader FileWriter FileInputStream FileOutputStream Memory: array CharArrayReader CharArrayWriter ByteArrayInputStream ByteArrayOutputStream Memory: string StringReader StringWriter N/A Pipe PipedReader PipedWriter PipedInputStream PipedOutputStream Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services A Simple Example This program performs a copy file operation using a manual buffer: java TestNodeStreams file1 file2 1 2 3 4 5 6 7 8 9 10 11 12 import java.io.*; public class TestNodeStreams { public static void main(String[] args) { try { FileReader input = new FileReader(args[0]); FileWriter output = new FileWriter(args[1]); char[] buffer = new char[128]; int charsRead; // read the first buffer charsRead = input.read(buffer); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
Sun Services A Simple Example 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 while ( charsRead != -1 ) { // write the buffer out to the output file output.write(buffer, 0, charsRead); // read the next buffer charsRead = input.read(buffer); } input.close(); output.close(); } catch (IOException e) { e.printStackTrace(); } } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Buffered Streams This program performs a copy file operation using a built-in buffer: java TestBufferedStreams file1 file2 1 2 3 4 5 6 7 8 9 10 11 12 13 import java.io.
Sun Services Buffered Streams 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 while ( line != null ) { // write the line out to the output file bufOutput.write(line, 0, line.length()); bufOutput.newLine(); // read the next line line = bufInput.readLine(); } bufInput.close(); bufOutput.close(); } catch (IOException e) { e.printStackTrace(); } } } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services I/O Stream Chaining Input Stream Chain Data Source Program FileInputStream BufferedInputStream DataInputStream Output Stream Chain Program Data Sink FileOutputStream BufferedOutputStream DataOutputStream Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Processing Streams Type Character Streams Byte Streams Buffering BufferedReader BufferedWriter BufferedInputStream BufferedOutputStream Filtering FilterReader FilterWriter FilterInputStream FilterOutputStream Converting between bytes and character InputStreamReader OutputStreamWriter Performing object serialization Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Processing Streams Type Character Streams Performing data conversion Byte Streams DataInputStream DataOutputStream Counting LineNumberReader LineNumberInputStream Peeking ahead PushbackReader PushbackInputStream Printing PrintWriter PrintStream Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The InputStream Class Hierarchy FileInputStream ObjectInputStream PipedInputStream DataInputStream InputStream SequenceInputStream PushbackInputStream FilterInputStream BufferedInputStream StringBufferInputStream LineNumberInputStream ByteArrayInputStream Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The OutputStream Class Hierarchy FileOutputStream ObjectOutputStream DataOutputStream OutputStream FilterOutputStream BufferedOutputStream PrintStream PipedOutputStream ByteArrayOutputStream Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Reader Class Hierarchy BufferedReader LineNumberReader CharArrayReader StringReader Reader InputStreamReader FileReader PipedReader FilterReader Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services The Writer Class Hierarchy BufferedWriter CharArrayWriter StringWriter Writer OutputStreamWriter FileWriter PrintWriter PipedWriter FilterWriter Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Module 15 Networking Java™ Programming Language
Sun Services Objectives • Develop code to set up the network connection • Understand the TCP/IP Protocol • Use ServerSocket and Socket classes for implementation of TCP/IP clients and servers Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Relevance How can a communication link between a client machine and a server on the network be established? Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Networking This section describes networking concepts. Sockets • Sockets hold two streams: an input stream and an output stream. • Each end of the socket has a pair of streams. Setting Up the Connection Set up of a network connection is similar to a telephone system: One end must dial the other end, which must be listening. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Networking client.bar.com 18000 server.foo.com 3000 client.baz.com 18002 Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Networking With Java Technology • To address the connection, include the following: • The address or name of remote machine • A port number to identify the purpose at the server • Port numbers range from 0–65535. Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Java Networking Model Server ServerSocket (port #) ServerSocket.accept() Register with this service Wait for a connection Socket() OutputStream Client Socket (host, port#) (Attempt to connect) OutputStream InputStream InputStream Socket.close() Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved. Sun Services, Revision F Socket.
Sun Services Minimal TCP/IP Server 1 2 3 4 5 6 7 8 9 10 11 12 13 import java.net.*; import java.io.*; public class SimpleServer { public static void main(String args[]) { ServerSocket s = null; // Register your service on port 5432 try { s = new ServerSocket(5432); } catch (IOException e) { e.printStackTrace(); } Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Minimal TCP/IP Server 14 15 16 17 18 19 20 21 22 23 24 25 26 27 // Run the listen/accept loop forever while (true) { try { // Wait here and listen for a connection Socket s1 = s.accept(); // Get output stream associated with the socket OutputStream s1out = s1.getOutputStream(); BufferedWriter bw = new BufferedWriter( new OutputStreamWriter(s1out)); // Send your string! bw.write(“Hello Net World!\n”); Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Minimal TCP/IP Server 28 29 30 31 32 33 34 35 36 37 38 39 40 41 // Close the connection, but not the server socket bw.close(); s1.close(); } catch (IOException e) { e.printStackTrace(); } // END of try-catch } // END of while(true) } // END of main method } // END of SimpleServer program Java™ Programming Language Copyright 2005 Sun Microsystems, Inc. All Rights Reserved.
Sun Services Minimal TCP/IP Client 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 import java.net.*; import java.io.*; public class SimpleClient { public static void main(String args[]) { try { // Open your connection to a server, at port 5432 // localhost used here Socket s1 = new Socket("127.0.0.1", 5432); // Get an input stream from the socket InputStream is = s1.
Sun Services Minimal TCP/IP Client 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 // Read the input and print it to the screen System.out.println(dis.readUTF()); // When done, just close the steam and connection dis.close(); s1.close(); } catch (ConnectException connExc) { System.err.println("Could not connect."); } catch (IOException e) { // ignore } // END of try-catch } // END of main method } // END of SimpleClient program Java™ Programming Language Copyright 2005 Sun Microsystems, Inc.
