CSE333

Java-1.1

The Java Language and EnvironmentThe Java Language and Environment

Cecilia Bastarrica, Anupama Vadali, andProf. Steven A. Demurjian, Sr.

Computer Science & Engineering DepartmentThe University of Connecticut371 Fairfield Road, Box U-255

Storrs, CT 06269-2155

steve@engr.uconn.eduhttp://www.engr.uconn.edu/

~stevehttp://www.engr.uconn.edu/cse

(860) 486 - 4818

CSE333

Java-1.2

Overview of PresentationOverview of Presentation

Motivation and Introduction to Java Motivation and Introduction to Java Designing and Developing Applets in JavaDesigning and Developing Applets in Java The Java User Interface - GUI with AWTThe Java User Interface - GUI with AWT Designing and Developing Java Classes Designing and Developing Java Classes Inheritance and Interfaces in JavaInheritance and Interfaces in Java Polymorphism and Object SerializationPolymorphism and Object Serialization

CSE333

Java-1.3

Motivation and Introduction to JavaMotivation and Introduction to Java

Java is Emerging as the OO Language of ChoiceJava is Emerging as the OO Language of Choice Java’s Utilization in … Java’s Utilization in …

Distributed Internet-Based Applications of All Types

Legacy/COTS Integration for Enterprise Computing

General-Purpose, Single-CPU Development Significant Dissemination on WWW:Significant Dissemination on WWW:

http://www.javasoft.com http://www.gamelan.com

We’ll Overview Key Features and CapabilitiesWe’ll Overview Key Features and Capabilities

CSE333

Java-1.4

An Overview of JavaAn Overview of Java

Java is a Third Generation, General Purpose, Java is a Third Generation, General Purpose, Platform Independent, Concurrent, Class-Based, Platform Independent, Concurrent, Class-Based, Object-Oriented Language and EnvironmentObject-Oriented Language and Environment

Java Composed of JDK and JREJava Composed of JDK and JRE Java LanguageJava Language Java Packages (Libraries)Java Packages (Libraries) javac Compiler to Bytecode (p-code)javac Compiler to Bytecode (p-code) JDB Java Debugger JDB Java Debugger Java Interpreter - Platform SpecificJava Interpreter - Platform Specific

JDK: Java Development EnvironmentJDK: Java Development Environment http://www.javasoft.com/products/jdk/1.2/http://www.javasoft.com/products/jdk/1.2/

JRE: Java Runtime EnvironmentJRE: Java Runtime Environment http://www.javasoft.com/products/jdk/1.2/jre/index.html

CSE333

Java-1.5

What is Java?What is Java?Software Releases and IDEsSoftware Releases and IDEs

Java is Free!Java is Free! Current Releases Current Releases

Version 2 for Win95, Win98, NT Version 2 (Early Access) for Solaris

Third-Party Ports to All Conceivable HW/SW Third-Party Ports to All Conceivable HW/SW Platforms from Micros to Mainframes Platforms from Micros to Mainframes

http://www.javasoft.com/cgi-bin/java-ports.cgi

Integrated Development Environments (IDEs) Integrated Development Environments (IDEs) Commercial Products, Freeware, Visual IDEs Visual J++, Visual Café, Kawa, Jpad, Javelin

CSE333

Java-1.6

Java Virtual Machine (JVM)Java Virtual Machine (JVM)

JVM is a JVM is a Platform Specific ProgramPlatform Specific Program which which Interprets and Executes Java CodeInterprets and Executes Java Code

JVM Interprets and Executes BytecodesJVM Interprets and Executes Bytecodes

JVM Targeted as Small/Efficient - Embeddable JVM Targeted as Small/Efficient - Embeddable within Consumer Electronicswithin Consumer Electronics

JVM Stack Based Machine - Simulates Real JVM Stack Based Machine - Simulates Real ProcessorProcessor

CA FE BA BE 00 03 00 2D 00 3ECA FE BA BE 00 03 00 2D 00 3E08 00 3B 08 00 01 08 00 20 0808 00 3B 08 00 01 08 00 20 08

CSE333

Java-1.7

Java Visualization Java Visualization

CSE333

Java-1.8

Packages In JavaPackages In Java

Allows Related Classes to be Grouped into a Allows Related Classes to be Grouped into a Larger AbstractionLarger Abstraction Similar to Ada95 Packages Unavailable in C++

Utilization of Packages for SW Design and Utilization of Packages for SW Design and DevelopmentDevelopment Components, Modularization, Groupings Enforcement by Compiler of Package Rules

Overall, Packages Enhance the Control and Overall, Packages Enhance the Control and Visibility to Fine-Tune Visibility to Fine-Tune Who Can See What When

CSE333

Java-1.9

The Java API PackagesThe Java API Packages

Application Programming Interface (API)Application Programming Interface (API) Java Defined - Building Blocks/LibrariesJava Defined - Building Blocks/Libraries Java Platform 1.2/2 Core APIJava Platform 1.2/2 Core API

java.applet java.rmijava.awt java.rmi.dgcjava.awt.datatransfer java.rmi.registryjava.awt.event java.rmi.serverjava.awt.image java.securityjava.beans java.security.acljava.io java.security.interfacesjava.lang java.sqljava.lang.reflect java.textjava.math java.utiljava.net java.util.zip

Power of Java Contained with APIsPower of Java Contained with APIs

CSE333

Java-1.10

The Java LanguageThe Java Language

Overview of Non-OO CapabilitiesOverview of Non-OO Capabilities Based on C/C++ No includes, typedefs, structures, groups Unicode Character Set - 34,168 Characters Automatic Coercions Not Supported Strongly-Type Language

Variables in JavaVariables in Java Primitive Types: ints, floats, booleans,

Unicode chars Reference Types: arrays, classes, interfaces

No Physical Pointers in Java!No Physical Pointers in Java!

CSE333

Java-1.11

The Java LanguageThe Java Language

Statements in Java - Resembles C and C++Statements in Java - Resembles C and C++ Assignment/Expressions and Precedence for, while, do-while if-then, switch-case break, continue, label, return

Exception HandlingException Handling Similar to C++ try, throws, catch Blocks Strongly Integrated Throughout APIs

CSE333

Java-1.12

The Java LanguageThe Java LanguageMotivating the Class ConceptMotivating the Class Concept

Conceptually, Classes are Structures/Records Conceptually, Classes are Structures/Records with Functions that are Encapsulatedwith Functions that are Encapsulated

structure Item { int UPC, OnShelf, InStock, ROLimit; char* Name; float RCost, WCost;

Status Create_New_Item(int UPC, ...); NameCost* Get_Item_NameCost(int UPC); void Modify_Inventory(int UPC, int Delta) ; Boolean Check_If_On_Shelf(int UPC); Boolean Time_To_Reorder(int UPC); };

NameCost *nc;Item I1, I2;I1.Create_New_Item(...);nc = I2.Get_Item_NameCost(UPC);

CSE333

Java-1.13

The Java LanguageThe Java LanguageObject-Oriented FeaturesObject-Oriented Features

Class - similar to C++ ClassClass - similar to C++ Class Classes have Classes have MembersMembers ( (MethodsMethods and and VariablesVariables)) Members Tagged Using Members Tagged Using KeywordsKeywords

private: Typically, Inaccessible public: Potential to be Accessible protected: Accessible via Inheritance package: Accessible within Package

Involve Visible Between Classes, Within Involve Visible Between Classes, Within Packages, and Due to InheritancePackages, and Due to Inheritance

CSE333

Java-1.14

Classes in JavaClasses in Java

A Supermarket ItemA Supermarket Item Keywords must be Utilized for Each Attribute Keywords must be Utilized for Each Attribute

or Method Declarationor Method Declaration

class Item { private String UPC, Name; private int Quantity; private double RetailCost; protected double WholeCost;

public Item() { ... }; public void finalize() { ... }; public boolean Modify_Inventory(int Delta){...}; public int Get_InStock_Amt() {return Quantity;};};

CSE333

Java-1.15

Classes in JavaClasses in Java

class Item { private String UPC, Name; private int Quantity; private double RetailCost; protected double WholeCost;

public Item() { ... }; public void finalize() { ... }; public boolean Modify_Inventory(int Delta) { int i = Get_InStock_Amt (); if (Delta >= 0) { Quantity += Delta; return true; } else { return false;} }; public int Get_InStock_Amt() {return Quantity;}; public double Compute_Item_Profit() {...}; protected boolean Modify_WholeSale(); {...};};

CSE333

Java-1.16

Visibility of Attributes/MethodsVisibility of Attributes/Methods

Class Members (Attributes and Methods)Class Members (Attributes and Methods) Visibility Tags for MembersVisibility Tags for Members

Private: Visible only to Class Protected: Visible to Class and Other Classes

within Package Public: Visible to Class, Other Classes within

Package, and if Class is Public, Visible to Other Packages/Classes

No Tag: Visible Only to Other Classes within Defining Package

Java's Controlled Sharing within/between Packages Java's Controlled Sharing within/between Packages not Supported in C++not Supported in C++

Abstraction/Encapsulation Superior in Java!Abstraction/Encapsulation Superior in Java!

CSE333

Java-1.17

Inheritance - Two RolesInheritance - Two Roles

Controlled Sharing Between ClassesControlled Sharing Between Classes Generalization vs. Specialization

Treat Instances of Different Classes in a Treat Instances of Different Classes in a Uniform FashionUniform Fashion Polymorphism and Dynamic Binding

Inheritance in JavaInheritance in Java

Item / \ DeliItem ProduceItem | SaladItem

class DeliItem extends Item { ... }; class SaladItem extends DeliItem { ... }; class ProduceItem extends Item { ... };

CSE333

Java-1.18

Designing and Developing Applets in JavaDesigning and Developing Applets in Java

Applets Small Independent Programs Intended for Applets Small Independent Programs Intended for Embedding into WWW Pages and Executable via Embedding into WWW Pages and Executable via Java-Enabled Browser (Netscape or IE)Java-Enabled Browser (Netscape or IE)

Applets Operate Under Severe Security Limits:Applets Operate Under Severe Security Limits: Can’t Execute Local Programs Can’t Communicate with Host Other than one

from Which Downloaded Can’t Read/Write to Local File System Can’t Find Information on Local System

Except Java/OS Versions and Character/Line Separators

CSE333

Java-1.19

Designing and Developing Applets in JavaDesigning and Developing Applets in Java

An Applet is a Java Program that Executes as An Applet is a Java Program that Executes as part of an HTML Pagepart of an HTML Page

appletA.java

appletA.class

javac

HTML file

...<APPLET CODE = “A.class”>

...

CSE333

Java-1.20

Applets Inheritance StructureApplets Inheritance Structure

java.lang.Objectjava.lang.Object

java.awt.Componentjava.awt.Component

java.awt.Containerjava.awt.Container

java.applet.Appletjava.applet.Applet

your appletyour applet

Everything in Java inherits from the Object class

Event-handling and drawing capabilities

Ability to hold components

Limits what an Applet can and cannot do

Every Applet is a subclass of the Applet class.

CSE333

Java-1.21

Applet Methods Eligible for OverridingApplet Methods Eligible for Overriding

Methods for MilestonesMethods for Milestones

initinit - initializes an - initializes an applet when it is loadedapplet when it is loaded

startstart - (re)starts applet’s - (re)starts applet’s executionexecution

stopstop - stops applet’s - stops applet’s executionexecution

destroydestroy - final cleanup - final cleanup before unloadingbefore unloading

Methods for DrawingMethods for Drawing

paintpaint updateupdate

The applet subclass must override at least one of these methods: init, start or paint.

CSE333

Java-1.22

Handling EventsHandling Events

Applets Handle Events by Implementing the Applets Handle Events by Implementing the Corresponding Corresponding interfaceinterface

import java.awt.event.MouseListener;import java.awt.event.MouseListener;import java.awt.event.MouseEvent;import java.awt.event.MouseEvent;……public class Simple extends Appletpublic class Simple extends Applet

implements implements MouseListener {MouseListener {

…… public void init() {public void init() { addMouseListener(this);addMouseListener(this); … … }} public void mouseClicked(MouseEvent event) {public void mouseClicked(MouseEvent event) { addItem(“click…”);addItem(“click…”); }}……}}

mouseClickedmouseEnteredmouseExitedmousePressedmouseReleased

Protocol of behavior

All methods in the interface must be implemented

CSE333

Java-1.23

Running an Applet in HTMLRunning an Applet in HTML

<APPLET CODE = <APPLET CODE = “AppletSubclass.class” WIDTH = “AppletSubclass.class” WIDTH = anIntanInt HEIGHT = HEIGHT = anIntanInt>>

</APPLET></APPLET>

The Browser:The Browser: Reserves a Display Area for the AppletReserves a Display Area for the Applet Loads the bytecodeLoads the bytecode Creates an Instance of the SubclassCreates an Instance of the Subclass Calls the Calls the initinit and and startstart Methods Methods

CSE333

Java-1.24

Loading an AppletLoading an Applet

Finding an AppletFinding an Applet CODEBASE Relative/Absolute Address

CODEBASE=“example/”CODEBASE=“http://someServer/…/otherDirectory/”

Bringing the AppletBringing the Applet Class by Class/Archives

HTMLfile Class

file

example

HTMLfile

Classfile

otherDirectory

CSE333

Java-1.25

The <APPLET> tagThe <APPLET> tag

<<APPLETAPPLET[[CODEBASECODEBASE = = codebaseURLcodebaseURL]]((CODECODE = = appletFileappletFile | | OBJECTOBJECT = = serializedAppletserializedApplet))[[ARCHIVEARCHIVE = = archivesListarchivesList]][[ALTALT = = alternateTextalternateText]][[NAMENAME = = appletInstanceNameappletInstanceName]]WIDTHWIDTH = = pixelspixels HEIGHTHEIGHT = = pixelspixels[[ALIGNALIGN = = alignmentalignment]][[VSPACEVSPACE = = pixelspixels] [] [HSPACEHSPACE = = pixelspixels]]>>[<[<PARAMPARAM NAMENAME = = appletParameter1appletParameter1 VALUEVALUE = = valuevalue>]>][<[<PARAMPARAM NAMENAME = = appletParameter2appletParameter2 VALUEVALUE = = valuevalue>]>]……[[alternateHTMLalternateHTML]]<</APPLET/APPLET>>

CSE333

Java-1.26

Security IssuesSecurity Issues

An Untrusted Applet Cannot:An Untrusted Applet Cannot: Load Libraries or Define Native Methods Read or Write Files on the Host that is

Executing the Applet Make Network Connections Except to the

Host from Which it was Loaded From Start any Program on the Host that is

Executing the Applet Get Many System Properties

CSE333

Java-1.27

Example of a GUI AppletExample of a GUI Applet

/* http://java.sun.com/docs/books/tutorial/ui/components/example//* http://java.sun.com/docs/books/tutorial/ui/components/example/ButtonDemo.java */ButtonDemo.java */

import java.awt.*;import java.awt.*;import java.awt.event.ActionListener;import java.awt.event.ActionListener;import java.awt.event.ActionEvent;import java.awt.event.ActionEvent;import java.applet.Applet;import java.applet.Applet;

public class ButtonDemo extends Appletpublic class ButtonDemo extends Applet implements ActionListener {implements ActionListener {

Button b1, b2, b3;Button b1, b2, b3;static final String DISABLE = "disable";static final String DISABLE = "disable";static final String ENABLE = "enable";static final String ENABLE = "enable";

public void init() {public void init() { b1 = new Button();b1 = new Button(); b1.setLabel("Disable middle button");b1.setLabel("Disable middle button"); b1.setActionCommand(DISABLE);b1.setActionCommand(DISABLE);

b2 = new Button("Middle button");b2 = new Button("Middle button");

b3 = new Button("Enable middle button");b3 = new Button("Enable middle button"); b3.setEnabled(false);b3.setEnabled(false); b3.setActionCommand(ENABLE);b3.setActionCommand(ENABLE);

CSE333

Java-1.28

Example of a GUI Applet (Continued)Example of a GUI Applet (Continued)

//Listen for actions on buttons 1 and 3.//Listen for actions on buttons 1 and 3. b1.addActionListener(this);b1.addActionListener(this); b3.addActionListener(this);b3.addActionListener(this);

//Add Components to the Applet, using the default FlowLayout. //Add Components to the Applet, using the default FlowLayout. add(b1);add(b1); add(b2);add(b2); add(b3);add(b3); }}

public void actionPerformed(ActionEvent e) {public void actionPerformed(ActionEvent e) { String command = e.getActionCommand();String command = e.getActionCommand(); if (command == DISABLE) { //They clicked "Disable middle button"if (command == DISABLE) { //They clicked "Disable middle button" b2.setEnabled(false);b2.setEnabled(false); b1.setEnabled(false);b1.setEnabled(false); b3.setEnabled(true);b3.setEnabled(true); } else { //They clicked "Enable middle button"} else { //They clicked "Enable middle button" b2.setEnabled(true);b2.setEnabled(true); b1.setEnabled(true);b1.setEnabled(true); b3.setEnabled(false);b3.setEnabled(false); }} }}}}

CSE333

Java-1.29

The Java User Interface - GUI with AWTThe Java User Interface - GUI with AWT

UI Refers to the Communications Between a UI Refers to the Communications Between a Program and a UserProgram and a User

Java Abstract Windowing Toolkit (AWT) and Java Abstract Windowing Toolkit (AWT) and Swing Contains Complete Set of Classes for Swing Contains Complete Set of Classes for Writing GUI ProgramsWriting GUI Programs

AWT Classes Categorized into: AWT Classes Categorized into: GUI Components Containers Layout Managers Drawing Event Handling

CSE333

Java-1.30

AWT ComponentsAWT Components

ButtonButton CheckBoxesCheckBoxes ChoicesChoices ListsLists MenusMenus TextfieldsTextfields Text AreasText Areas LabelsLabels

CSE333

Java-1.31

ContainersContainers

The Java AWT Provides Three Types of The Java AWT Provides Three Types of Containers Implemented as Subclasses of Containers Implemented as Subclasses of Container Class:Container Class: Window

Frame - creates a normal full fledged window to contain components

Dialog - provides a window that is dependent on another window

FileDialog - helps the user to open and save file Panel - Groups Components within an Area of

an Existing Window ScrollPane -Like Panel, Used to Display Large

Component in a Limited Amount of Space

CSE333

Java-1.32

Inheritance Hierarchies for ComponentsInheritance Hierarchies for Components

CSE333

Java-1.33

Layout ManagersLayout Managers

Layout Manager Controls the Size and Position of Layout Manager Controls the Size and Position of Components in a ContainerComponents in a Container

By Default Every Container Object has an By Default Every Container Object has an Associated LayoutMangerAssociated LayoutManger Panel Objects - FlowLayout Window Object - BorderLayout

CSE333

Java-1.34

Layout Managers - SimpleLayout Managers - Simple

FlowLayout FlowLayout Default for Panel

Objects Lays out Components

from Left to Right Starting New Rows if Needed

GridLayoutGridLayout Displays the

Components in Equal Size in the Requested Number of Rows and Columns

CSE333

Java-1.35

Layout Managers - Special PurposeLayout Managers - Special Purpose

BorderLayout BorderLayout Default for Window

Objects Uses 5 Areas to hold

Components: North, South, East, West, and Center

CardLayoutCardLayout One Area Contains

Different Components at Different Times

CSE333

Java-1.36

Layout Managers - FlexibleLayout Managers - Flexible

GridBagLayoutGridBagLayout Aligns Components by Placing them in a Grid

of Cells Allows some Components to Span more than

one Cell The Rows and Columns have Different Heights

and Widths

CSE333

Java-1.37

Example of a GUI appletExample of a GUI applet

CSE333

Java-1.38

Excerpts for GUI Applet ExampleExcerpts for GUI Applet Example(Note: Many Lines Omitted!!) (Note: Many Lines Omitted!!)

import java.applet.*;import java.awt.*;import Message;

public class Sample extends Applet { Panel p1, p2; Label l1, l2, l3, l4, l5; TextField name; TextArea address; Checkbox order; Choice size, color; Button ok, clear, quit ; Message message;

CSE333

Java-1.39

Excerpts for GUI Applet ExampleExcerpts for GUI Applet Example (Note: Many Lines Omitted!!) (Note: Many Lines Omitted!!)

public void init() { p1 = new Panel(); p2 = new Panel();

l1 = new Label("Name"); l2 = new Label("Address"); // … other labels omitted

name = new TextField(30);address = new TextArea(3, 30);

order = new Checkbox();size = new Choice();size.addItem("Small");size.disable();ok = new Button("OK");clear = new Button("Clear");quit = new Button("Quit");

p1.setLayout(new GridLayout(0,2,2,2));p1.add(l1);p1.add(name);p1.add(l2);p1.add(address);p1.add(l3);p1.add(order);p1.add(l4);p1.add(size);p1.add(l5);p1.add(color);p2.setLayout(new FlowLayout());p2.add(ok);p2.add(clear);p2.add(quit);setLayout(new BorderLayout());add("North", p1);add("South", p2);

}

CSE333

Java-1.40

Excerpts for GUI Applet ExampleExcerpts for GUI Applet Example (Note: Many Lines Omitted!!) (Note: Many Lines Omitted!!)

public boolean action(Event e, Object o){ if(e.target == ok)

{ // You must provide the actions/code}if(e.target == clear){ // You must provide the actions/code}if(e.target == quit){ // You must provide the actions/code

}if(e.target == order){

if(order.getState() == true){ // You must provide the actions/code}else if(order.getState() == false){ // You must provide the actions/code}

}return true;

}}

CSE333

Java-1.41

Event HandlingEvent Handling

When a User Acts on a Component, the AWT When a User Acts on a Component, the AWT Detects the Event and Notifies the Event ListenersDetects the Event and Notifies the Event Listeners

A Class Implements the Event Listener and Every A Class Implements the Event Listener and Every Class Instance can Register as Event ListenersClass Instance can Register as Event Listeners

Steps for Implementing and Registering:Steps for Implementing and Registering: Declare that a Class Implements a Listener

Interface in the Class declaration Implement the Listener methods in the Class Register an Instance of the Class as a Listener

on One or More Components

CSE333

Java-1.42

Example of Event HandlingExample of Event Handling

public class Beeper ... implements ActionListener { ... // where initialization occurs: button.addActionListener(this); ... public void actionPerformed(ActionEvent e)

{ // Make a beep sound ... }}

CSE333

Java-1.43

The AWT EventsThe AWT Events

Action Events Action Events Adjustment EventAdjustment Event Component Events Component Events Container EventsContainer Events Focus EventsFocus Events Item EventsItem Events Key EventsKey Events Mouse EventsMouse Events Mouse-Motion EventsMouse-Motion Events Text EventsText Events Window EventWindow Event

CSE333

Java-1.44

Action ListenersAction Listeners

Easiest Event Handlers to ImplementEasiest Event Handlers to Implement Generated by:Generated by:

Clicking a Button Double Clicking a List Item Choosing a Menu Item Pressing Return in a Text Field

Listener Interface - ActionListenerListener Interface - ActionListener Methods - actionPerformed(ActionEvent)Methods - actionPerformed(ActionEvent)

CSE333

Java-1.45

Action Listeners - ActionEventAction Listeners - ActionEvent

Parameter to the actionPerfomed MethodParameter to the actionPerfomed Method ActionEvent Defines Two Useful MethodsActionEvent Defines Two Useful Methods

String setActionCommand Associates a string to the action

String getActionCommand Returns the string associated with this action

CSE333

Java-1.46

Item ListenersItem Listeners

Generated by Components that Maintain State, Generated by Components that Maintain State, Generally on/off StateGenerally on/off State

Components that Generate ItemEvents:Components that Generate ItemEvents: Checkboxes Choices Lists

Listener Interface - ItemListenerListener Interface - ItemListener Methods - itemStateChanged(ItemEvent)Methods - itemStateChanged(ItemEvent)

CSE333

Java-1.47

ItemListeners - ItemEventItemListeners - ItemEvent

Parameter to the itemStateChanged MethodParameter to the itemStateChanged Method ItemEvent Defines Two Useful Methods:ItemEvent Defines Two Useful Methods:

Object getItem() Returns the component specific object associated

with the item whose state has changed int getStateChange()

Returns the new state of the item SELECTED = 1 DESELECTED = 0

CSE333

Java-1.48

Excerpts for GUI Applet with ListenerExcerpts for GUI Applet with Listener(Note: Many Lines Omitted!!) (Note: Many Lines Omitted!!)

import java.applet.*;import java.awt.*;import java.awt.event.*;import Message;

public class Sample1 extends Applet implements ActionListener, ItemListener

{// Declarations similar to previous example

static final String OK = "ok"; public void init() { // Init actions similar to previous example, // except for code shown below for checkbox and buttons order = new Checkbox(); order.addItemListener(this); ok = new Button("OK"); ok.setActionCommand(OK); ok.addActionListener(this); }

CSE333

Java-1.49

Excerpts for GUI Applet with ListenerExcerpts for GUI Applet with Listener(Note: Many Lines Omitted!!) (Note: Many Lines Omitted!!)

public void actionPerformed(ActionEvent e){ String command = e.getActionCommand();

if(command == OK) { // You must provide the actions/code }if(command == CLEAR) { // You must provide the actions/code }if(command == QUIT) { // You must provide the actions/code }

}

public void itemStateChanged(ItemEvent e1){ if(e1.getStateChange() == ItemEvent.SELECTED)

{ // You must provide the actions/code}else { // You must provide the actions/code}

}}

CSE333

Java-1.50

Designing and Developing Java ClassesDesigning and Developing Java Classes

Encapsulation Capabilities of JavaEncapsulation Capabilities of Java Classes (Data + Operations) - ADTs Packages - Collections of “Related” Classes

Class Declaration:Class Declaration: Access Modes and Variable Members Constructors and Class Bodies Method Declaration and Access Modes Class and Instance Members Garbage Collection

CSE333

Java-1.51

Class DefinitionClass Definition

public class Stack {public class Stack { private Vector items;private Vector items; public Stack() {public Stack() { items = new Vector(10);items = new Vector(10); }} public Stack(int numElem) {public Stack(int numElem) { items = new Vector(numElem);items = new Vector(numElem); }} public Object push(Object item) {public Object push(Object item) { item.addElement(item);item.addElement(item); return item;return item; }} public synchronized Object pop() {public synchronized Object pop() { int len = items.size();int len = items.size(); Object obj = null;Object obj = null; if (len == 0)if (len == 0) throw new EmptyStackException();throw new EmptyStackException(); obj = items.elementAt(len - 1);obj = items.elementAt(len - 1); items.removeElementAt(len - 1);items.removeElementAt(len - 1); return obj;return obj; }} public boolean isEmpty() {public boolean isEmpty() { if (items.size() == 0)if (items.size() == 0) return true;return true; elseelse return false;return false; }}}}

Class Body

Class DeclarationMemberVariable

Constructors

MemberMethods

CSE333

Java-1.52

PackagesPackages

A A packagepackage is a Collection of Related Classes and is a Collection of Related Classes and Interfaces that Provides Access Protection and Interfaces that Provides Access Protection and Namespace ManagementNamespace Management

File Name and Package Name IdenticalFile Name and Package Name Identical Packages are Imported via the Packages are Imported via the importimport Keyword Keyword

package graphics;class Circle extend Graphic implements Draggable { ... }class Rectangle extends Graphic implements Draggable { ... }interface Draggable { ... }

CSE333

Java-1.53

Access ModesAccess Modes

Constructors and Members Constructors and Members can be defined as:can be defined as: public: Any other class

can invoke them. protected: Only

subclasses and classes in the same package can invoke them.

private: Only accessible within the class.

package: Accessible only to other classes and interfaces declared in the same package (default if omitted).

Controls Encapsulation Controls Encapsulation and Allows Evolvability and Allows Evolvability with Minimal Impact on with Minimal Impact on other Classes that use the other Classes that use the MembersMembers

Deciding Appropriate Deciding Appropriate Access Mode Access Mode Determines Security and Determines Security and Ensures that Data Ensures that Data Remains in a Consistent Remains in a Consistent State.State.

CSE333

Java-1.54

ConstructorsConstructors

Utilized to Create a new Class instance by Utilized to Create a new Class instance by Reserving Sspace for the Member Variables Reserving Sspace for the Member Variables Rectangle rect = Rectangle rect = newnew Rectangle(); Rectangle();

Member Variable Initialization PossibleMember Variable Initialization Possible Constructors Mimic Class Name with No Return Constructors Mimic Class Name with No Return

TypeType Default Constructor with Empty Argument ListDefault Constructor with Empty Argument List Constructors may be OverloadedConstructors may be Overloaded

CSE333

Java-1.55

Variable MembersVariable Members

Declaration (Class Body)Declaration (Class Body) Defines the Type of a Variable

Instantiation (Constructor)Instantiation (Constructor) Reserves Memory for the New Instance

InitializationInitialization Assign Initial Value(s)

accessLevel Indicates the access level of this memberstatic Declares a class memberfinal Indicates that it is constanttransient This variable is transientvolatile This variable is volatiletype name The type and name of the variable

CSE333

Java-1.56

Method MembersMethod Members

DeclarationDeclaration Access Level

public, protected, private, or package Return Type

void or type return statement Either return the declared type or a subtype

Name Overloading Overriding

Arguments List of variable declarations Cannot include methods Argument names may hide member names: this

CSE333

Java-1.57

accessLevel Access level for this methodstatic This is a class methodabstract This method is not implementedfinal Method cannot be overridennative Method implemented in another languagesynchronized Method requires a monitor to runreturnType methodName The return type and the method name(paramlist) The list of argumentsthrows exceptions The exceptions thrown by this method

Method Members (cont.)Method Members (cont.)

CSE333

Java-1.58

ExampleExamplepublic class Point {public class Point { public int x = 0;public int x = 0; public int y = 0;public int y = 0;

public void move(int newX, int newY) {public void move(int newX, int newY) { x = newX;x = newX; y = newY;y = newY; }}}}

public class Line {public class Line { public Point origin;public Point origin; public Point end;public Point end;

public Line() {public Line() { origin = new Point();origin = new Point(); end = new Point();end = new Point(); }} public Line(Point origin, Point end) {public Line(Point origin, Point end) { this.origin = origin;this.origin = origin; this.end = end;this.end = end; }}}}

DefaultConstructor

Overloading

Hiding

origin end

x

y

x

y

aLineObject

LineInstance

PointInstances

CSE333

Java-1.59

Class and Instance MembersClass and Instance Members

Class Members are Defined with the Keyword Class Members are Defined with the Keyword staticstatic

Class Variables and Class Methods are Associated Class Variables and Class Methods are Associated with the Class Rather than each of its Instanceswith the Class Rather than each of its Instances

Class Variables are Shared Among all InstancesClass Variables are Shared Among all Instances JRE Creates one copy of Class Variables the First JRE Creates one copy of Class Variables the First

Time it Encounters a Containing InstanceTime it Encounters a Containing Instance Class Methods only Operate on Class VariablesClass Methods only Operate on Class Variables Class Bariables declared as Class Bariables declared as finalfinal are constants are constants Class Members are Accessible without the need to Class Members are Accessible without the need to

Instantiate the ClassInstantiate the ClassclassName.classMethod();className.classVar = 10;

CSE333

Java-1.60

Class and Instance Members (Continued)Class and Instance Members (Continued)

class AnInteger { int x; public int x() { return x; } public void setX(int newX) { x = newX; }}

class AnInteger { static int x; public int x() { return x; } public void setX(int newX) { x = newX; }}

…AnInteger myX = new AnInteger();AnInteger yourX = new AnInteger();myX.setX(1);yourX.x = 2;System.out.println(“myX = “ + myX.x());System.out.println(“yourX = “ + yourX.x());…

class AnInteger { int x; static public int x() { return x; } static public void setX(int newX){ x = newX; }}

CSE333

Java-1.61

Garbage CollectionGarbage Collection

Unreferenced Objects are Garbage Collected Unreferenced Objects are Garbage Collected AutomaticallyAutomatically

Memory is Freed for Later ReuseMemory is Freed for Later Reuse Garbage Collection runs in a Low Priority Thread, Garbage Collection runs in a Low Priority Thread,

either Synchronously or Asynchronouslyeither Synchronously or Asynchronously The The finalize()finalize() Method is Inherited from Method is Inherited from

ObjectObject and can be Overridden to Liberate and can be Overridden to Liberate ResourcesResources

CSE333

Java-1.62

Inheritance in JavaInheritance in Java

Basic Definitions and ConceptsBasic Definitions and Concepts Generalization vs. Specialization Subclass vs. Superclass

Acquisition Rules Acquisition Rules What Does Superclass Pass to Subclass? What Does Subclass Inherit from Superclass? What is Visible within Packages? Overriding vs. Overloading?

Role of Public, Final, and Abstract ClassesRole of Public, Final, and Abstract Classes Java Interfaces for Design-Level Multiple Java Interfaces for Design-Level Multiple

Inheritance and Quasi GenericsInheritance and Quasi Generics

CSE333

Java-1.63

Inheritance - Terms and ConceptsInheritance - Terms and Concepts

Every Class in Java is Derived from the Object Every Class in Java is Derived from the Object ClassClass

Java Classes can be Organized into Hierarchies Java Classes can be Organized into Hierarchies Using the Using the extendsextends Keyword Keyword

Establishing Establishing Superclass/SubclassSuperclass/Subclass Relationships Relationships Between the Classes in ApplicationBetween the Classes in Application

A A SuperclassSuperclass Contains Members Common to Its Contains Members Common to Its SubclassesSubclasses - - GeneralizationGeneralization

SubclassesSubclasses Contain Members Different from Contain Members Different from Shared Shared SuperclassSuperclass - - SpecializationSpecialization

Only Single Inheritance is Supported in Java at Only Single Inheritance is Supported in Java at Implementation Level!Implementation Level!

CSE333

Java-1.64

Subclass & SuperclassSubclass & Superclass

Subclass Subclass Subclass is a Class that Extends Another Class Inherits State and Behavior from all of its

Ancestors Subclass can use the Inherited Member

Variables and Functions oror hide the Inherited Member Variables and Override the Inherited Member Functions

SuperclassSuperclass Superclass is a Class’s Direct Ancestor

CSE333

Java-1.65

A Superclass in JavaA Superclass in Java

A Supermarket ItemA Supermarket Item Keywords must be Utilized for Each Attribute Keywords must be Utilized for Each Attribute

or Method Declarationor Method Declaration

class Item { private String UPC, Name; private int Quantity; private double RetailCost; protected double WholeCost;

public Item() { ... }; public void finalize() { ... }; public boolean Modify_Inventory(int Delta){...}; public int Get_InStock_Amt() {return Quantity;};};

CSE333

Java-1.66

Inheritance - Defining Subclasses in JavaInheritance - Defining Subclasses in Java

ItemItem / \/ \ DeliItem ProduceItemDeliItem ProduceItem || SaladItemSaladItem

class DeliItem extends Item { ... }; class SaladItem extends DeliItem { ... }; class ProduceItem extends Item { ... };

CSE333

Java-1.67

Members Inherited By a SubclassMembers Inherited By a Subclass

Subclass Inherits all Public/Protected Members Subclass Inherits all Public/Protected Members of a Superclassof a Superclass DeliItem Inherits Public/Protected from

Item Subclass Inherits all Package Members of Subclass Inherits all Package Members of

Classes in the same Package as the SubclassClasses in the same Package as the Subclass All superclass Members can be Declared with All superclass Members can be Declared with

no Access Specification, if Subclass is in the no Access Specification, if Subclass is in the Same Package as the SuperclassSame Package as the Superclass

CSE333

Java-1.68

Members Not Inherited By A SubclassMembers Not Inherited By A Subclass

Subclass does not Inherit Private Members of a Subclass does not Inherit Private Members of a SuperclassSuperclass DeliItem doesn’t Inherit Private from Item

Subclasses do not Inherit a Superclass’s Member if Subclasses do not Inherit a Superclass’s Member if the Subclass Declares a Member with Same Namethe Subclass Declares a Member with Same Name Member Variables - Subclass Hides the

Member Variable of the Superclass Member Methods - Subclass Overrides the one

in the Superclass

CSE333

Java-1.69

Hiding Member Variables Hiding Member Variables and Overriding Member Methodsand Overriding Member Methods

class parentClass {boolean state;void setState() {

state = true;}

}class childClass extends parentClass {

boolean state;void setState() {

state = false;super.setState();System.out.println(state);System.out.println(super.state)

}}

CSE333

Java-1.70

Overriding Member MethodsOverriding Member Methods

Subclasses CANNOT Override Methods that are Subclasses CANNOT Override Methods that are Declared to be Final in the SuperclassDeclared to be Final in the Superclass

Subclasses MUST Override Methods that are Subclasses MUST Override Methods that are Declared as Abstract in the SuperclassDeclared as Abstract in the Superclass

Subclasses MUST be Declared as Abstract if they Subclasses MUST be Declared as Abstract if they do not Override Abstract Methods from the do not Override Abstract Methods from the SuperclassSuperclass

CSE333

Java-1.71

Methods Inherited From Methods Inherited From ObjectObject Class Class

The Java “The Java “ObjectObject” Class Defines Basic State and ” Class Defines Basic State and Behavior of all Classes and Their InstancesBehavior of all Classes and Their Instances

User Defined Classes can Override these Methods:User Defined Classes can Override these Methods: clone equals finalize toString hashCode

User Defined Classes Cannot Override: User Defined Classes Cannot Override: getClass notify notifyAll wait

CSE333

Java-1.72

Public, Final, and Abstract ClassesPublic, Final, and Abstract Classes

Public ClassesPublic Classes Within Package, public Classes Become

Visible to Outside World Public Members are Exported

Final ClassesFinal Classes Prohibits Subclassing for Security Final Class Prevents Access of Protected

Members via Subclassing Not Supported in C++/Ada95

Abstract ClassesAbstract Classes Can't be Instantiated No Implementations for Abstract Methods

CSE333

Java-1.73

Final Classes and Final Classes and the “Final” Keywordthe “Final” Keyword

A Class is Declared as Final - the Class Cannot be A Class is Declared as Final - the Class Cannot be Subclassed.Subclassed. For Security For Design

A Method is Declared as Final in a Class - any A Method is Declared as Final in a Class - any Subclass Cannot Override that MethodSubclass Cannot Override that Method

A Variable is Declared as Final - the Variable is a A Variable is Declared as Final - the Variable is a Constant and it Cannot be ChangedConstant and it Cannot be Changed

CSE333

Java-1.74

Abstract Classes And MethodsAbstract Classes And Methods

Abstract ClassesAbstract Classes Cannot be Instantiated Can only be Subclassed Keyword “abstract” before Keyword “class” is

used to Define an Abstract Class Example of an Abstract Class is Number in the

java.lang Package Abstract MethodsAbstract Methods

Abstract Classes may contain Abstract Methods

This allows an Abstract Class to Provide all its Subclasses with the Method Declarations for all the Methods

CSE333

Java-1.75

A Sample Abstract ClassA Sample Abstract Class

abstract class Item { protected String UPC, Name; protected int Quantity; protected double RetailCost, WholeCost;

public Item() { ... }; abstract public void finalize(); abstract public boolean Modify_Inventory(int Delta); public int Get_InStock_Amt() {...}; public double Compute_Item_Profit() {...}; protected boolean Modify_WholeSale(double NewPrice);{...}; };

CSE333

Java-1.76

Another Abstract Class and MethodsAnother Abstract Class and Methods

abstract class GraphicsObject{int x, y;void moveTo(int x1,y1) { . . . . . }abstract void draw();

}

class Circle extends GraphicsObject{void draw() { . . . . . }

}

class Rectangle extends GraphicsObject{void draw() { . . . . . }

CSE333

Java-1.77

Interfaces in JavaInterfaces in Java

Design-Level Multiple InheritanceDesign-Level Multiple Inheritance Java InterfaceJava Interface

Set of Methods (no Implementations) Set (Possibly Empty) of Constant Values

Interfaces Utilized Extensively Throughout Java Interfaces Utilized Extensively Throughout Java APIs to Acquire and Pass on FunctionalityAPIs to Acquire and Pass on Functionality Threads in Java - Multiple Concurrent Tasks Subclassing from Thread Class (java.lang API) Implementing an Interface of Runnable Class

CSE333

Java-1.78

A Sample Interface in JavaA Sample Interface in Java

Teaching

Student Employee / \ | UnderGrad Graduate Faculty

interface Teaching { int NUMSTUDENTS = 25; void recordgrade(Undergrad u, int score); void advise(Undergrad u); ... etc ... }

class Graduate extends Student implements Teaching{ ...}

class Faculty extends Employee implements Teaching{ ...}

recordgrade() Different for Graduate & Faculty

CSE333

Java-1.79

Quasi Generics in JavaQuasi Generics in Java

interface Coll { int MAXIMUM = 500; void add(Object obj); void delete(Object obj); Object find(Object obj); int currentCount();}

class Set implements Coll{ void add(Object obj){ ... } void delete(Object obj){ ... }}

class Queue implements Coll{ void add(Object obj){ ... } void delete(Object obj){ ... }}

CSE333

Java-1.80

Polymorphism and Polymorphism and Object Serialization in JavaObject Serialization in Java

PolymorphismPolymorphism Polymorphism via Dispatching Allows a

Runtime or Dynamic Choice of the Method to be Called based on the Class Type of the Invoking Instance

Promotes Reuse and Evolution of Code Polymorphism/Dispatching Incurs Cost or

Overhead at both Compile and Runtime! SerializationSerialization

Conversion of Object to Format that Facilitates Storage to File or Transfer Across Network

Process Controlled via API with Minimal Interaction by Software Engineer

CSE333

Java-1.81

PolymorphismPolymorphism

SubstitutabilitySubstitutability Whenever Value of a Certain Type is

Expected, a Subtype can also be Provided In Context of Inheritance, All Subclasses can

be Treated as Common Root Class Simplifies Code and Facilitates Reuse

Static TypeStatic Type Type Defined in the Variable Declaration

Dynamic TypeDynamic Type Type of the Actual Value held by the Variable

at Runtime

CSE333

Java-1.82

PolymorphismPolymorphism

A Variable is Polymorphic Whenever it may have A Variable is Polymorphic Whenever it may have Different Static and Dynamic TypesDifferent Static and Dynamic Types Static Variable I1 Defined with Type Item Dynamic Variable Access Allows I1.Print()

to be Invoked on DeliItem, ProduceItem, etc., Instances

Problems:Problems: Reverse Polymorphism: Can we get the

Subtype Variable Back After Assigning its Value to a Supertype?

Method Binding: When Invoking a Method on a Variable, should it be Selected According to its Static or Dynamic Type?

CSE333

Java-1.83

An ExampleAn Example

We have a class We have a class BallBall, and , and two subclasses two subclasses WhiteBallWhiteBall and and BlackBallBlackBall

The The SelectOneSelectOne() method () method gets a gets a WhiteBallWhiteBall and a and a BlackBallBlackBall as arguments and as arguments and returns one of them returns one of them selected randomly selected randomly

Questions:Questions: What is SelectOne()’s

return type? How can we know

which ball was returned?

SelectOne

?

CSE333

Java-1.84

Dynamic Binding and CastingDynamic Binding and Castingpublic class Ball { public String id = new String("I'm a

ball");

public String GetId() { return id; }}public class WhiteBall extends Ball { public String id = new String("I'm

white"); public String GetId() { return id; } public void OnlyWhite() { System.out.println("Yes, I'm

white"); }}public class BlackBall extends Ball { public String id = new String("I'm

black"); public String GetId() { return id; } public void OnlyBlack() { System.out.println("Yes, I'm

black"); }}

class balls {class balls { public static void main(String[] args) public static void main(String[] args)

{{ WhiteBall wb = new WhiteBall();WhiteBall wb = new WhiteBall(); BlackBall bb = new BlackBall();BlackBall bb = new BlackBall(); Ball b = SelectOne(wb, bb);Ball b = SelectOne(wb, bb); System.out.println(b.GetId());System.out.println(b.GetId()); System.out.println(b.id);System.out.println(b.id); if (b instanceof WhiteBall) {if (b instanceof WhiteBall) { wb = (WhiteBall)b;wb = (WhiteBall)b; wb.OnlyWhite();wb.OnlyWhite(); } else {} else { bb = (BlackBall)b;bb = (BlackBall)b; bb.OnlyBlack();bb.OnlyBlack(); }} }} public static Ball SelectOne(WhiteBall public static Ball SelectOne(WhiteBall

w, BlackBall b) {w, BlackBall b) { if (Math.random() > 0.5)if (Math.random() > 0.5) return w;return w; elseelse return b;return b; }}}}

The static type of b is Ball, but its dynamic type is either WhiteBallor BlackBall.

What is going to be printed?

CSE333

Java-1.85

Class Student (Superclass) - Maintains Class Student (Superclass) - Maintains Student InformationStudent Information

public class Student{ // protected used to facilitate

inheritance protected String name, SSN; protected float gpa; // constructor used to initialize

object public Student(String n, String

ssn,float g) { name = n; SSN = ssn; gpa = g; }

public String getName() { return name; }

public float getGpa() { return gpa; }

public String getSSN() { return SSN; }

// diplay student information public void print() { System.out.println("Student

name: " + name); System.out.println("

SSN: " + SSN); System.out.println("

gpa: " + gpa); }}

CSE333

Java-1.86

Class GradClass Grad

public class Grad extends Student{ private String thesis; public Grad(String name, String ssn, float gpa, String t) { // call parent's constructor super(name, ssn, gpa); thesis = t; }

public String getThesis() { return thesis; }

public void print() { super.print(); System.out.println(" thesis: " + thesis); }}

CSE333

Java-1.87

Class UndergradClass Undergrad

public class Undergrad extends Student { private String advisor; private String major;

public Undergrad(String name, String ssn, float gpa, String adv, String maj){

super(name, ssn, gpa); advisor = adv; major = maj; } public String getAdvisor() { return advisor; }

public String getMajor() { return major; }

public void print() { super.print(); System.out.println(" advisor: " + advisor); System.out.println(" major: " + major); }}

CSE333

Java-1.88

Class StudentDBClass StudentDB

import java.util.Vector;

public class StudentDB{ private Vector stuList;

// constructor public StudentDB(int size){ // allocate memory for

vector stuList = new

Vector(size); }

// returns number of students stored

public int numOfStudents() { return (stuList.size()); }

public void insert(Student s) { stuList.addElement(s); }

// search for student by name public Student

findByName(String name){ Student stu = null; //

temp student boolean found = false; int count = 0; int DBSize =

stuList.size(); while ((count < DBSize)||

(found == false)){ stu = (Student)

stuList.elementAt(count); if

(stu.getName().equals(name))

found = true;

count++; } return stu; }

CSE333

Java-1.89

Class StudentDB (Continued)Class StudentDB (Continued)

public Student remove(String name) { Student stu = null; // temp

student boolean found = false; int count = 0; int DBSize = stuList.size(); while ((count < DBSize) ||

(found == false)){ stu = (Student)

stuList.elementAt(count); if

(stu.getName().equals(name)) found = true; count++; } if (found == true)

stuList.removeElementAt(count - 1);

return stu; }

public void displayAll() { int DBSize =

stuList.size(); for (int i = 0; i <

DBSize; i++) { Student stu = (Student)

stuList.elementAt(i); stu.print(); System.out.println(); } }}

CSE333

Java-1.90

Class MainInterfaceClass MainInterface

public class MainInterface{ private StudentDB db;

public static void main(String[] args) {

MainInterface studentInt = new MainInterface();

studentInt.displayMenu(); } // constructor public MainInterface() { db = new StudentDB(5); }

public void displayMenu(){ int option = 0; System.out.println("\n 1. Insert "); System.out.println(" 2. Delete "); System.out.println(" 3. Search "); System.out.println(" 4. Display "); System.out.println(" 5. Exit \n"); option = Console.readInt("Enter your

choice: "); while (option > 0 && option < 5) { processOption(option); System.out.println("\n 1. Insert "); System.out.println(" 2. Delete"); System.out.println(" 3. Search "); System.out.println(" 4. Display "); System.out.println(" 5. Exit \n"); option = Console.readInt("Enter your

choice: "); } }

CSE333

Java-1.91

Class MainInterface (Continued)Class MainInterface (Continued)

public void processOption(int option) { String name, SSN; float gpa; switch (option){ case 1: int type = Console.readInt("1. Grad or 2. Undergrad? "); name = Console.readString(“Name: "); SSN = Console.readString(“SSN: "); gpa = (float) Console.readDouble("gpa: "); if (type == 1){ String thesis = Console.readString("Enter thesis title:"); Student g = new Grad(name, SSN, gpa, thesis); db.insert(g); }

CSE333

Java-1.92

Class MainInterface (Continued)Class MainInterface (Continued)

else{ String advisor = Console.readString("Enter

advisor:"); String major = Console.readString("Enter major: "); Student u = new Undergrad(name, SSN, gpa, advisor,

major); db.insert(u); } break; case 2: name = Console.readString(”Name"); Student s = db.remove(name); s.print(); break;

CSE333

Java-1.93

Class MainInterface (Continued)Class MainInterface (Continued)

case 3: name = Console.readString("Enter name: "); Student stu = db.findByName(name); System.out.println(); stu.print(); break; case 4: System.out.println(); db.displayAll(); } }}

CSE333

Java-1.94

Object SerializationObject Serialization

Object Serialization is the Process of Reading Object Serialization is the Process of Reading and Writing Objectsand Writing Objects Bi-directional Process of Write (Save in

Serialized form) and Read (Reconstruct from Serialized form)

ObjectInputStream and ObjectOutputStream are ObjectInputStream and ObjectOutputStream are used for Reading and Writing Objectsused for Reading and Writing Objects

Used in:Used in: Remote Method Invocation (RMI) Lightweight Persistence - Archival for Use

in a Later Invocation of a Program Exchange of Information Across Network Agent-Based/Aglet Computing

CSE333

Java-1.95

Using Object SerializationUsing Object Serialization

Straightforward Process in JavaStraightforward Process in Java Serialize Objects by ...Serialize Objects by ...

Writing Objects to an ObjectOutputStream Deserialize Objects by ...Deserialize Objects by ...

Reading Objects using ObjectInputStream Design/Develop Classes that Promote the Design/Develop Classes that Promote the

Serialization/Deserialization of InstancesSerialization/Deserialization of Instances Serialize/Deserialize at Topmost Level:Serialize/Deserialize at Topmost Level:

Automatically Includes Component Instances, Set and Collection Instances, User-Defined Class Instances, etc.

Whatever is Declared with Class and Active within Instance

CSE333

Java-1.96

Writing to an ObjectOutputStreamWriting to an ObjectOutputStream

The Following Code Segment Serializes the Date The Following Code Segment Serializes the Date ObjectObject FileOutputStream out = new

FileOutputStream("theTime"); ObjectOutputStream s = new ObjectOutputStream(out); s.writeObject("Today"); s.writeObject(new Date()); s.flush();

Serializes the Object to a File named “theTime”Serializes the Object to a File named “theTime”

CSE333

Java-1.97

Reading From an ObjectInputStreamReading From an ObjectInputStream

The Following Code Segment Reconstructs by The Following Code Segment Reconstructs by Deserializing the Date Object:Deserializing the Date Object:

FileInputStream in = new FileInputStream("theTime");ObjectInputStream s = new ObjectInputStream(in);String today = (String)s.readObject();Date date = (Date)s.readObject();

Object and its Components (if any) are Read from Object and its Components (if any) are Read from the File “theTime”the File “theTime”

If Multiple Independent Objects were Written, If Multiple Independent Objects were Written, Objects must be Read in the Same Order Objects must be Read in the Same Order

Return Value from readObject has to be Cast to a Return Value from readObject has to be Cast to a Specific TypeSpecific Type

CSE333

Java-1.98

Utilizing Object SerializationUtilizing Object Serialization

Serialization/Deserialization Occurs via the Serialization/Deserialization Occurs via the Implementation of the Java Serializable InterfaceImplementation of the Java Serializable Interface

An Object is Serializable only if its Class An Object is Serializable only if its Class Implements the Serializable InterfaceImplements the Serializable Interface Serialization Utilizes Exception Handling For Example, writeObject Method Throws a

NotSerializableException if the given Object is not serializable

Serializable is an Empty InterfaceSerializable is an Empty Interface Does not Contain Any Method Declarations Identifies Classes whose Objects are

Serializable

CSE333

Java-1.99

Implementing the Serializable InterfaceImplementing the Serializable Interface

The Serializable InterfaceThe Serializable Interface public interface Serializable

{ // there's nothing in here!}; To make Instances of a Vlass serializable, add the To make Instances of a Vlass serializable, add the

Implements Serializable to Class Defenition Implements Serializable to Class Defenition public class MySerializableClass implements

Serializable { … } User does not have to Write any Methods

Serialization of Objects are Handled by the Serialization of Objects are Handled by the defaultWriteObject Method of the defaultWriteObject Method of the ObjectOutputStream ObjectOutputStream

CSE333

Java-1.100

defaultWriteObject MethoddefaultWriteObject Method

The defaultWriteObject Method is Defined in The defaultWriteObject Method is Defined in ObjectOutputStream ClassObjectOutputStream Class

defaultWriteObject Writes all Necessary Details to defaultWriteObject Writes all Necessary Details to Reconstruct an Instance of the ClassReconstruct an Instance of the Class Class of the Object Class Signature Values of Non-Transient and Non-Static

Members Including References to Other Contained Objects

In Turn, Contained Objects, their Classes, Signatures, Values, etc., are also Written

Process Continues in a Logically Recursive Fashion