Lecture by : Mr. Tushar Gohil Lecturer,

8/14/2019 Lecture by : Mr. Tushar Gohil Lecturer,

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AppletsApplets

Lecture By :

Mr. Tushar Gohil

Lecturer, I.T. Department

SCET,Surat.


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IntroductionIntroduction

An Applets are small applications that areaccessed on an internet server, transportedover a internet, automatically installed &

run as a part of web document in Javacompatible web browser.

Its Execution is under the control of JVM.

An applet can react to user input &dynamically respond.


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Applet v/s ApplicationsApplet v/s Applications

Applications are the programs that runs onyour computer , under the OS of thatcomputer.

Applets are designed to be transmittedover the internet & executed by a Java

Compatible web browser.


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SimpleAppletSimpleApplet

import java.awt.*;

import java.applet.*;

public class SimpleApplet extends Applet {

public void paint(Graphics g) {

g.drawString("A Simple Applet", 20, 20);}

}

Applets interacts with user through the AWT, not through consolebased I/O classes. The AWT (Abstract Windows Toolkit) containssupport for window based graphical interface.

Paint() is defined by AWT. This method is called each time the appletmust be redisplay its output.


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How to Run appletsHow to Run applets

Applets does not have main method.

Java Enable Web browser

Appletviewer


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Java Enabled Web browser

3. Create a HTML File (RunApp.html) and write this code into it

4. Open a RunApp.html or c:\>appletviewer RunApp.html

RunApp.html


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Appletviewer

3. Include this code in your applet

4. C:\>appletviewer SimpleApplet.java

import java.awt.*;


/*

*/

public class SimpleApplet extends Applet {



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Applet ArchitectureApplet Architecture

Applets are event driven. An Applet waits until an eventoccurs. The AWT notifies the Applet about an event bycalling an event handler that has been provided by theApplet. Once this happens the applet must take

appropriate action and then quickly return control back toAWT.

User initiates the interaction with an applet, not the other

way around.


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Applet SkeletonApplet Skeleton

All but most trivial applets override a set of methods thatprovides the basic mechanism by which the browser orappletviewer interfaces to the applet and controls itsexecution.


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// An Applet skeleton.

import java.awt.*;


/*

*/

public class AppletSkel extends Applet {

public void init() { // Called first.

// initialization}

public void start() { /* Called second, after init(). Also called whenever the applet is restarted. */

// start or resume execution

}

public void paint(Graphics g) { // Called when an applet's window must be restored.

// redisplay contents of window

}

public void stop() { // Called when the applet is stopped.

// suspends execution

}

public void destroy() { /* Called when applet is terminated. This is the last method executed. */

// perform shutdown activities

}}


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11

The Life-Cycle of AppletThe Life-Cycle of Applet

init() Called exactly once in an applets life.

Called when applet is first loaded, which is

after object creation, e.g., when the browservisits the web page for the first time.

Used to read applet parameters, start

downloading any other images or media

files, etc.


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Applet Life-Cycle (Cont.)Applet Life-Cycle (Cont.)

start() Called at least once.

Called when an applet is started or

restarted, i.e., whenever the browser visitsthe web page.

stop() Called at least once.

Called when the browser leaves the web

page.


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13


paint() Called each time when your applets output

needs to be redrawn.

The Graphics parameter is used wheneveroutput to the applet is required.

destroy() Called exactly once.

Called when the browser unloads the applet.

Used to perform any final clean-up.


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14


start

paint

stop

destroyinit


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Skeleton.java

import java.awt.*;


/*

*/

public class Skeleton extends Applet{

String msg;

public void init() {

msg = "Inside init( ) --";

}

public void start() {

msg += " Inside start( ) --";

}


msg += " Inside paint( ).";

g.drawString(msg, 10, 30);

}

public void stop() {

msg += " Inside stop( ) --";

}

}


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Applets Simple Display MethodsApplets Simple Display Methods

void drawString(String message, int x, int y)void setBackground(Color newColor)

void setForeground(Color newColor)

Color getBackground( )

Color getForeground( )

Here, newColor specifies the new color. The class Colordefines the constants shown here that can be used tospecify colors:

Color.black Color.magentaColor.blue Color.orange

Color.cyan Color.pink

Color.darkGray Color.red

Color.gray Color.white

Color.green Color.yellowColor.lightGray


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/* A simple applet that sets the foreground and

background colors and outputs a string. */

import java.awt.*;


/*

*/

public class Sample extends Applet{

String msg;

// set the foreground and background colors.

public void init() {setBackground(Color.cyan);

setForeground(Color.red);

msg = "Inside init( ) --";

}

// Initialize the string to be displayed.

public void start() {msg += " Inside start( ) --";

}

// Display msg in applet window.


msg += " Inside paint( ).";


}


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Requesting RepaintRequesting Repaint

Whenever your applet needs to update the informationdisplayed in its window, simply call the repaint() method.

It is defined by AWT. It causes the update() to be calledwhich in turn in its default implementation calls paint().

void repaint( ) void repaint(int left, int top, int width, int height)

void repaint(long maxDelay)

void repaint(long maxDelay, intx, int y, int width, int height)

maxDelay specifies the maximum number of milliseconds that can elapsebefore update( ) is called. Beware, though, If the time elapses beforeupdate( ) can be called, it isnt called.


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Scrolling Message AppletScrolling Message Appletimport java.awt.*;


/*

*/

public class SimpleBanner extends Applet

implements Runnable {

String msg = " A Simple Moving Banner.";Thread t = null;

boolean stopFlag;

// Set colors and initialize thread.


setBackground(Color.cyan);

setForeground(Color.red);

}

// Start thread

public void start() {

t = new Thread(this);

stopFlag = false;

t.start();

}

public void run() {

char ch;

for( ; ; ) {

try {

repaint();

Thread.sleep(250);

ch = msg.charAt(0);

msg = msg.substring(1, msg.length());

msg += ch;

if(stopFlag)

break;

} catch(InterruptedException e) {}

}

}

public void stop() {

stopFlag = true;

t = null;

}



}

}


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Using the Status BarUsing the Status BarshowStatus(String s)

import java.awt.*;


/*

*/

public class StatusWindow extends Applet{


setBackground(Color.cyan);

}


g.drawString("This is in the applet window.", 10, 20);

showStatus("This is shown in the status window.");

}

}


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Passing Parameters to AppletPassing Parameters to Applet// Use Parameters

import java.awt.*;


/*

*/


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Passing Parameters to AppletPassing Parameters to Appletpublic class ParamDemo extends Applet{

String fontName;int fontSize;

float leading;

boolean active;

// Initialize the string to be displayed.

public void start() {String param;

fontName = getParameter("fontName");

param = getParameter("fontSize");

fontSize = Integer.parseInt(param);

param = getParameter("leading");leading = Float.valueOf(param).floatValue();

param = getParameter("accountEnabled");

active = Boolean.valueOf(param).booleanValue();

}


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Passing Parameters to AppletPassing Parameters to Applet// Display parameters.


g.drawString("Font name: " + fontName, 0, 10);

g.drawString("Font size: " + fontSize, 0, 26);

g.drawString("Leading: " + leading, 0, 42);

g.drawString("Account Active: " + active, 0, 58);

}

}


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Delegation Event Model

defines standard and consistent mechanisms togenerate and process events

a source generates an event and sends it to one ormore listeners

the listener simply waits until it receives an event.

Once received, the listener processes the event andthen returns

A user interface element is able to delegate theprocessing of an event to a separate piece of code

In the delegation event model, listeners must registerwith a source in order to receive an eventnotification. so notifications are sent only to listenersthat want to receive them


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Events

An event is an object that describes a state changein a source.

It can be generated as a consequence of a personinteracting with the elements in a graphical userinterface

i.e. pressing button, keyboard, timer expires


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Events Sources

A source is an object that generates an event.

This occurs when the internal state of that objectchanges in some way. Sources may generate morethan one type of event.

A source must register listeners in order for thelisteners to receive notifications about a specific

type of event. Each type of event has its own registration method.

Here is the general form

public void addTypeListener(TypeListener el)

i.e. addKeyListener() , addMouseListner()


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Events Sources (Cont.)

When an event occurs, all registered listeners arenotified and receive a copy of the event object.

to remove a registration of listenerpublic void removeTypeListener(TypeListener el)

i.e. removeKeyListener() , removeMouseListner()


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Events Listeners

A listener is an object that is notified when anevent occurs.

It has two major requirements.

1) It must have been registered with one or moresources to receive notifications about specific typesof events.

2) it must implement methods to receive andprocess these notifications.


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Events Classes (Cont..)

EventObject (java.util)

Root Class of All the Event Classes

Constructors :

EventObject(Object src)

Mehods :Object getSource()


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AWTEvent

superclass of all AWT events that are handled by thedelegation event model.

Mehods :

int getID()

returns the type of event


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ActionEvent

It is generated when a button is pressed, a list item isdouble-clicked, or a menu item is selected

Constructors :

ActionEvent(Object src, int type, String cmd)

ActionEvent(Object src, int type, String cmd, int modifiers)

ActionEvent(Object src, int type, String cmd, long when, intmodifiers)

Integer Constants (Modifiers):

ALT_MASK,CTRL_MASK,META_MASK & SHIFT_MASK.

Type :

ACTION_PERFORMED


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ActionEvent (Cont..)

Methods:

String getActionCommand( )

To obtain the command name for the invoking ActionEvent object

int getModifiers( )

Returns a value that indicates which modifier keys (ALT, CTRL, META,

and/or SHIFT) were pressed when the event was generated.

long getWhen( )

Returns the time at which the event took place.


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AdjustmentEvent

It is generated by a scroll bar.

Constructors :

AdjustmentEvent(Adjustable src, int id, int type, int data)

Integer Constants (Type):

BLOCK_DECREMENT : clicked inside the scroll bar to decrease its value.

BLOCK_INCREMENT : clicked inside the scroll bar to increase its value.

TRACK : The slider was dragged.

UNIT_DECREMENT : The button at the end of the scroll bar was clicked todecrease its value.

UNIT_INCREMENT : The button at the end of the scroll bar was clicked toincrease its value.

ID :

ADJUSTMENT_VALUE_CHANGED


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EventsClasses (Cont..)

AdjustmentEvent (Cont..)

Methods:

Adjustable getAdjustable( )

returns the object that generated the event.

int getAdjustmentType( )

It returns one of the constants defined by AdjustmentEvent.


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ComponentEvent

It is generated when the size, position, or visibility of a component ischanged.

Constructors :ComponentEvent(Component src, int type)

Integer Constants (Type): COMPONENT_HIDDEN : The component was hidden. COMPONENT_MOVED : The component was moved. COMPONENT_RESIZED : The component was resized. COMPONENT_SHOWN : The component became visible.

Methods

Component getComponent()


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ContainerEventIt is generated when a component is added to or removed froma container.

Constructors :ContainerEvent(Component src, int type, Component comp)


COMPONENT_ADDED COMPONENT_REMOVED

Methods

Component getContainer( )

Component getChild()


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Events Classes (Cont..) FocusEvent

It is generated when a component gains or loses input focus.

Constructors :

FocusEvent(Component src, int type)FocusEvent(Component src, int type, boolean temporaryFlag)

Focus Event(Component src, int type, boolean temporaryFlag, Componentother)

Integer Constants (Type): FOCUS_GAINED FOCUS_LOST

MethodsComponent getOppositeComponent( )

boolean isTemporary( )


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Events Classes (Cont..) InputEvent Abstract class Subclass of ComponentEvent Superclass for component input events (i.e. KeyEvent ,MouseEvent )

Integer Constants (Type):ALT_MASK ALT_DOWN_MAST

SHIFT_MASK etc.

CTRL_MASK

Methodsboolean isAltDown( )

boolean isControlDown( )

boolean isMetaDown( )

boolean isShiftDown( )

int getModifiers( )


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Events Classes (Cont..) KeyEvent

It is generated when keyboard input occurs.

Constructors :KeyEvent(Component src, int type, long when, int modifiers, int code)

KeyEvent(Component src, int type, long when, int modifiers, int code, char ch)

Integer Constants (Type): KEY_PRESSED

KEY_RELEASED

KEY_TYPED

Integer Constants (Code):VK_0 through VK_9 , VK_A through VK_Z

VK_ENTER VK_ESCAPE VK_CANCEL VK_UP

VK_DOWN VK_LEFT VK_RIGHT VK_PAGE_DOWN

VK_PAGE_UP VK_SHIFT VK_ALT VK_CONTROL

Methods

char getKeyChar( )

int getKeyCode()


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Events Classes (Cont..) MouseEvent

Constructors :MouseEvent(Component src, int type, long when, int modifiers, intx, inty, int clicks, boolean triggersPopup)

Integer Constants (Type): MOUSE_CLICKED The user clicked the mouse.

MOUSE_DRAGGED The user dragged the mouse.

MOUSE_ENTERED The mouse entered a component.

MOUSE_EXITED The mouse exited from a component.

MOUSE_MOVED The mouse moved.

MOUSE_PRESSED The mouse was pressed.

MOUSE_RELEASED The mouse was released. MOUSE_WHEEL The mouse wheel was moved

Methods

int getX( )

int getY( )


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Events Classes (Cont..) MouseWheelEvent

Constructors :

MouseWheelEvent(Component src, int type, long when, int modifiers, intx, int y, int clicks, boolean triggersPopup, int scrollHow, int amount, intcount)

Integer Constants (Type): WHEEL_BLOCK_SCROLL A page-up or page-down scroll event occurred. WHEEL_UNIT_SCROLL A line-up or line-down scroll event occurred.

Methodsint getScrollType( )


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Events Classes (Cont..) WindowEvent

Constructors :WindowEvent(Window src, int type)


WINDOW_ACTIVATED The window was activated. WINDOW_CLOSED The window has been closed.

WINDOW_CLOSING The user requested that the window be closed. WINDOW_DEACTIVATED The window was deactivated. WINDOW_DEICONIFIED The window was deiconified. WINDOW_GAINED_FOCUS The window gained input focus. WINDOW_ICONIFIED The window was iconified. WINDOW_LOST_FOCUS The window lost input focus.

WINDOW_OPENED The window was opened.


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| Some event classes of package| Some event classes of package java.awt.eventjava.awt.event ..


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Events Listeners

Listeners are created by implementing one ormore of the interfaces defined by the

java.awt.event package.

When an event occurs, the event source invokesthe appropriate method defined by the listenerand provides an event object as its argument.


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ActionListener Interface

This interface defines the actionPerformed( ) methodthat is invoked when an action event occurs.

Methods :

void actionPerformed(ActionEvent ae)


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AdjustmentListener Interface

Methods :

void adjustmentValueChanged(AdjustmentEvent ae)


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Events Classes (Cont..) ComponentListener Interface

Methods :

void componentResized(ComponentEvent ce)

void componentMoved(ComponentEvent ce)

void componentShown(ComponentEvent ce)

void componentHidden(ComponentEvent ce)


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Events Classes (Cont..) FocusListener Interface

Methods :

void focusGained(FocusEvent fe)

void focusLost(FocusEvent fe)


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Events Classes (Cont..) KeyListener Interface

Methods :

void keyPressed(KeyEvent ke)

void keyReleased(KeyEvent ke)

void keyTyped(KeyEvent ke)


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Events Classes (Cont..) MouseListener Interface

Methods :

void mouseClicked(MouseEvent me)

void mouseEntered(MouseEvent me)

void mouseExited(MouseEvent me)

void mousePressed(MouseEvent me)void mouseReleased(MouseEvent me)


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Events Classes (Cont..) MouseMotionListener Interface

Methods :

void mouseDragged(MouseEvent me)

void mouseMoved(MouseEvent me)


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54 Some common event-listener interfacesSome common event-listener interfaces


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Using Delegation Event Model

Just follow these two steps:

3. Implement the appropriate interface in the listenerso that it will receive the type of event desired.

5. Implement code to register and unregister (ifnecessary) the listener as a recipient for the eventnotifications.

Handling Mouse Events


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Handling Mouse Eventspublic class MouseEvents extends Applet

implements MouseListener, MouseMotionListener {

String msg = "";

int mouseX = 0, mouseY = 0;public void init() {

addMouseListener(this);

addMouseMotionListener(this);

}

// Display msg in applet window at current X,Ylocation.


g.drawString(msg, mouseX, mouseY);

}

// Handle mouse clicked.

public void mouseClicked(MouseEvent me) {

// save coordinates

mouseX = 0;

mouseY = 10;

msg = "Mouse clicked.";

repaint();

}

// Handle mouse entered.

public void mouseEntered(MouseEvent me) {

mouseX = 0;

mouseY = 10;msg = "Mouse entered.";

repaint();

}

// Handle mouse exited.

public void mouseExited(MouseEvent me) {mouseX = 0;

mouseY = 10;

msg = "Mouse exited.";

repaint();

}

public void mousePressed(MouseEvent me) {

mouseX = me.getX();

mouseY = me.getY();

msg = "Down";

repaint();

}

Handling Mouse Events


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Handling Mouse Events// Handle button released.

public void mouseReleased(MouseEvent me) {

// save coordinates

mouseX = me.getX();mouseY = me.getY();

msg = "Up";

repaint();

}

// Handle mouse dragged.

public void mouseDragged(MouseEvent me) {

// save coordinates

mouseX = me.getX();

mouseY = me.getY();

msg = "*";

showStatus("Dragging mouse at " + mouseX + ", " + mouseY);

repaint();

}

// Handle mouse moved.

public void mouseMoved(MouseEvent me) {

// show status

showStatus("Moving mouse at " + me.getX() + ", " + me.getY());

}

}

Handling Key Events


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Handling Key Eventspublic class SimpleKey extends Applet

implements KeyListener {

String msg = "";

int X = 10, Y = 20; // output coordinates


addKeyListener(this);

}

public void keyPressed(KeyEvent ke) {

showStatus("Key Down");

}public void keyReleased(KeyEvent ke) {

showStatus("Key Up");

}

public void keyTyped(KeyEvent ke) {

msg += ke.getKeyChar();

repaint();}

// Display keystrokes.


g.drawString(msg, X, Y);

}

}

Adapter Classes


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Adapter Classes

An Adapter class provides an empty implementation of all

methods in an event listener interface. Adapter Classes are useful when you want to receive and

process only some of the events that are handled by aparticular interface.

You can define a new class to act as a event listener byextending one of the adapter classes and implementing only

those methods in which you are interested.

public class AdapterDemo extends Applet {



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p () {

addMouseListener(new MyMouseAdapter(this));

addMouseMotionListener(new MyMouseMotionAdapter(this));

}

}

class MyMouseAdapter extends MouseAdapter {

AdapterDemo adapterDemo;

public MyMouseAdapter(AdapterDemo adapterDemo) {

this.adapterDemo = adapterDemo;

}

public void mouseClicked(MouseEvent me) {

adapterDemo.showStatus("Mouse clicked");

}

}

class MyMouseMotionAdapter extends MouseMotionAdapter {

AdapterDemo adapterDemo;

public MyMouseMotionAdapter(AdapterDemo adapterDemo) {

this.adapterDemo = adapterDemo;

}

public void mouseDragged(MouseEvent me) {

adapterDemo.showStatus("Mouse dragged");

}}

Inner Classes


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Inner Classes

Inner Classes are a classes which are defined within otherclass.


MousePressedDemo mousePressedDemo;

public MyMouseAdapter(MousePressedDemo mousePressedDemo) {

this.mousePressedDemo = mousePressedDemo;

}public void mousePressed(MouseEvent me) {

mousePressedDemo.showStatus("Mouse Pressed.");

}

}

public class MousePressedDemo extends Applet {public void init() {

addMouseListener(new MyMouseAdapter(this));

}

}

Inner Classes


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Inner Classes

public class InnerClassDemo extends Applet {


addMouseListener(new MyMouseAdapter());

}



showStatus("Mouse Pressed");

}

}

}

Anonymous Inner Classes


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Anonymous Inner Classes

public class AIDemo extends Applet {public void init() {

addMouseListener(new MouseAdapter() {


showStatus("Mouse Pressed");

}});

}

}

An Anonymous class is one that is not assigned a name. The syntax new MouseAdapter( ) { ... } indicates to the

compiler that the code between the braces defines ananonymous inner class. Furthermore, that class extendsMouseAdapter. This new class is not named, but it isautomatically instantiated when this expression is executed

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Lecture by : Mr. Tushar Gohil Lecturer,