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Applets

Object

Component

ButtonTextComponent

Checkbox ChoiceContainer

Label

TextArea TextField

ScrollBar Canvas

Panel ScrollPaneWindow

Part of the AWT Class Hierarchy

Dialog FrameApplet

List

Client

Web Server

Internet

TCP/IP(HTTP)

TCP/IP(HTTP)

Java Security ModelJava Security Model

TCP/IP(socket)

TCP/IP(socket)

Sambar ServerSambar ServerHTML files(Applet Tags)HTML files(Applet Tags)

Applets Applets

Netscape(JVM)Netscape(JVM) Loads HTML fileLoads HTML file Loads Java AppletLoads Java Applet

Java Security ModelJava Security Model

•Restricted Access to Local File SystemRestricted Access to Local File System

•Restricted Access to Outside ServersRestricted Access to Outside Servers

•Restricted Access to ThreadsRestricted Access to Threads

Java AppletJava Applet

public class className extends java.applet.Applet {

public void init() {}

public void paint(Graphics g) {}}

Java AppletJava Applet

Applets will have the following methods:Applets will have the following methods:

publicpublic voidvoid init ( ) { init ( ) { //in here you will //in here you will

//set fonts –may be done in//set fonts –may be done in paint paint instead instead

//set initial background and foreground collors//set initial background and foreground collors

//initialize attributes (if other than their defaults)//initialize attributes (if other than their defaults)

//add components and/or event listeners//add components and/or event listeners

}}

publicpublic voidvoid actionListenerType (EventType e) { actionListenerType (EventType e) {

////needed for event driven applets – may occur in a component subclass

//do some action that will change the applet display//do some action that will change the applet display

repaint();repaint();

}}

publicpublic voidvoid paint(Graphics g) { paint(Graphics g) {

//only implicitly called by repaint//only implicitly called by repaint

}}

Additional Applet MethodsAdditional Applet Methods

publicpublic voidvoid start ( ) { start ( ) {

//called after init and before the first invocation of paint//called after init and before the first invocation of paint

//if applet is stopped and restarted, start is called//if applet is stopped and restarted, start is called

//Netscape calls start and stop when the browser window is resized//Netscape calls start and stop when the browser window is resized

//IE and appletviewer don’t//IE and appletviewer don’t

}}

publicpublic voidvoid stop() { stop() {

//called when user leaves page containing the applet//called when user leaves page containing the applet

}}

publicpublic voidvoid destroy() { destroy() {

//called when applet is about to be permanently destroyed –//called when applet is about to be permanently destroyed –

//when browser shuts down or when ir removes the applet from memory//when browser shuts down or when ir removes the applet from memory

//Called by IE when user leaves the page containing the applet//Called by IE when user leaves the page containing the applet

}}

import java.awt.Graphics; import java.awt.Font; import java.awt.Color; import java.applet.Applet;

public class HelloWorldApplet1 extends Applet {

Font f = new Font("TimesRoman", Font.BOLD, 36); String name,greeting;

public void init() { name = ”Roger L. Norton"; greeting = new String("Hello " + name + "!"); }

public void paint(Graphics g) { g.setFont(f); g.setColor(Color.red); g.drawString(greeting, 5, 40); }}

HelloWorldApplet1.javaHelloWorldApplet1.java

Java HTML APPLET Tag Java HTML APPLET Tag

<APPLET CODE= “…” WIDTH = xxx HEIGHT= yyy …><APPLET CODE= “…” WIDTH = xxx HEIGHT= yyy …>

……..</APPLET></APPLET>

Options:Options:

CODEBASECODEBASE

ALIGNALIGN

HSPACEHSPACE

VSPACEVSPACE

NAMENAME

ARCHIVEARCHIVE Designates an archive of classes to preloadDesignates an archive of classes to preload

Designates the applet alignment choice Designates the applet alignment choice (Left, Right, Top, Bottom, Middle)(Left, Right, Top, Bottom, Middle)

Designates the empty space at the right and left of the appletDesignates the empty space at the right and left of the applet

Designates the empty space above and below the appletDesignates the empty space above and below the applet

Designates the name of the appletDesignates the name of the applet

Designates the base URLDesignates the base URL

<HTML> <HEAD> <TITLE> Hello World Example! </TITLE> </HEAD> <BODY> <H2> Event Driven Software Java Lecture 2 </H2> <P> <APPLET code="HelloWorldApplet1.class" width="500" height="50"> Hello World! </APPLET> </P> <P> <A href="HelloWorldApplet1.java">The Source</A> </P> </BODY></HTML>

Java HTML APPLET Tag Java HTML APPLET Tag

<APPLET CODE= “…” WIDTH = xxx HEIGHT= yyy …><APPLET CODE= “…” WIDTH = xxx HEIGHT= yyy …>

Some text to be displayed if browser does not support javaSome text to be displayed if browser does not support java

<PARAM NAME = “…” VALUE = “…”><PARAM NAME = “…” VALUE = “…”>

<PARAM NAME = “…” VALUE = “…”><PARAM NAME = “…” VALUE = “…”>

</APPLET></APPLET>

<HTML> <HEAD> <TITLE> Hello World Example! </TITLE> </HEAD> <BODY> <H2> Event Driven Software Java Lecture 1 </H2> <P> <APPLET code="HelloWorldApplet.class" width="500" height="50"> <PARAM name="name" value="Roger L. Norton"> Hello World! </APPLET> </P> <P> <A href="HelloWorldApplet.java">The Source</A> </P> </BODY></HTML>

HellowWorldApplet2.htmlHellowWorldApplet2.html

<HTML> <HEAD> <TITLE> Hello World Example! </TITLE> </HEAD> <BODY> <H2> Event Driven Software Java Lecture 1 </H2> <P> <APPLET code="HelloWorldApplet.class" width="500" height="50"> Hello World! </APPLET> </P> <P> <A href="HelloWorldApplet.java">The Source</A> </P> </BODY></HTML>

HelloWorldApplet3.htmlHelloWorldApplet3.html

import java.awt.Graphics; import java.awt.Color;

public class ColorBoxes extends java.applet.Applet {

void delay(int time){ for(int i =1;i<=time;i++); }

public void paint(Graphics g) { int rval, gval, bval; String tempDelay = getParameter("delay"); int finalDelay = Integer.parseInt(tempDelay);

for (int k = 1;k<=100;k++){ for (int j = 30; j < (size().height -25); j += 30) for (int i = 5; i < (size().width -25); i += 30) { rval = (int)Math.floor(Math.random() * 256); gval = (int)Math.floor(Math.random() * 256); bval = (int)Math.floor(Math.random() * 256);

g.setColor(new Color(rval,gval,bval)); g.fillRect(i, j, 25, 25); g.setColor(Color.black); g.drawRect(i, j, 25, 25); }; delay(finalDelay); }; };}

An Interesting ExampleAn Interesting Example

<HTML> <HEAD> <TITLE> Colored Boxes </TITLE> </HEAD> <BODY> <H2> Event Driven Software Example #3 </H2> <H2> Colored Boxes </H2> <P> <APPLET code="ColorBoxes.class" width="600" height="300"> <PARAM name="delay" value="10000000"> </APPLET> </P> <P> <A href="ColorBoxes.java">The Source</A> </P> </BODY></HTML>

ColorBoxes.htmlColorBoxes.html

Events in JavaEvents in Java

In Java most objects within the AWT class hierarchy have the ability to observe events In Java most objects within the AWT class hierarchy have the ability to observe events occurring with respect to itself (e.g. a occurring with respect to itself (e.g. a buttonbutton can observe that it has been pressed, or a can observe that it has been pressed, or a textbox textbox can detect that it has been written to). The object can then send this can detect that it has been written to). The object can then send this information to any other object that has indicated it is interested in knowing about information to any other object that has indicated it is interested in knowing about such happeningssuch happenings. . These notified objects can then react to these events.These notified objects can then react to these events.

ButtonButton ButtonPanelButtonPanel

ActionEventActionEvent

addActionListener(this)addActionListener(this)

actionPerformed(ActionEvent)actionPerformed(ActionEvent)

buttonPressedbuttonPressedgetObjecct()getObjecct()

Events in JavaEvents in Java

ButtonButton ButtonPanelButtonPanel

ActionEventActionEvent

addActionListeneraddActionListener(this)(this)

(ActionEvent actionPerformed)(ActionEvent actionPerformed)

buttonPressedbuttonPressedgetObjecctgetObjecct()()

A listener object:A listener object:

implements a “listener interface”implements a “listener interface”

can be registered as a listener to various event sourcescan be registered as a listener to various event sources

An event source:An event source:

can register listener objectcan register listener object

can send listeners “event objects”can send listeners “event objects”

An event object:An event object:

contains information about the event that occurredcontains information about the event that occurred

can be queried to receive this informationcan be queried to receive this information

Event Listeners for Mouse and Keyboard EventsEvent Listeners for Mouse and Keyboard Events

MouseListenerMouseListener

public void mouseEntered(MouseEvent e)

public void mouseExited (MouseEvent e)

public void mousePressed (MouseEvent e)

public void mouseReleased (MouseEvent e)

public void mouseClicked (MouseEvent e)

KeyListenerKeyListener

public void keyPressed(KeyEvent e)

public void keyReleased(keyEvent e)

public void keyTyped(keyEvent e)

MouseMotionListenerMouseMotionListener

public void mouseMoved (MouseEvent e)

public void mouseDragged (MouseEvent e)

Pressed and released at same location

Keyboard and Mouse EventsKeyboard and Mouse Events

AWTEvent contains four important methods:

consume //delete the event

isConsumed //returns boolean – true if consumed by another

//listener on same source

getID //and int represening the event type

getSource //the Object that the event came from

KeyEvent adds the following methods:

getKeyChar //returns character typed

setKeyChar //replace the character with a different one

getKeyCode //returns an integer value which can be passedto

//getKeyText

isActionKey //differentiates function and arrow keys from normal key

getModifiers setModifiers //retrieve/replace modifier keys

isAltDown, isShiftDown, isControlDown

Keyboard and Mouse EventsKeyboard and Mouse Events

MouseEventMouseEvent methods methods:

getX, getY //determine location of the mouse event

getClickCount //differentiates between single and double clicks

getModifiers //to determine which button was pressed

Event Handling ExamplesEvent Handling Examples

Clicks Example 1Clicks Example 1



Colors ExampleColors Example

Text ExampleText Example

Testing an AppletTesting an Applet

Construct an HTML file that will locate your applet in a region of an html page.

Run appletviewer with the name of the html file where you call your applet.

Documents

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