Java - Event Listeners Example in Java Applet

Introduction

The event listener is the feature of java that handles the several events for the several objects, Such as: MouseEvent, KeyEvent, TextEvent, InputEvent etc. Classes for helping in implementing event listeners are present in the java.awt.event.*; package. So, to use the events handling in your application import the java.awt.event.*; package. This example illustrates that how to handle several events fired on the several objects.

In this example you will see that how to use the event listener and to perform appropriate tasks. In this example the EventListeners.java is our applet class which implements the ActionListener interface. Here four buttons and integer types variables have been used with specific values to perform the Addition, Subtraction, Multiplication and Division operations. All these operations are controlled by the events generated by these buttons. The Text Area named txtArea holds the result of the operation. There are two methods like init() and actionPerformed() have been used in this program for performing the whole operation.

To handle the events generated by these buttons you add action listeners

e.g. object_name.addActionListener(this);.

When the action event occurs, that object's actionPerformed method is invoked.

actionPerformed(ActionEvent e)

Here is the java code of the program:


import java.applet.*;

 import java.awt.event.*;

 import java.awt.*;
  

 public class EventListeners extends Applet implements ActionListener{

   TextArea txtArea;

   String Add, Subtract,Multiply,Divide;

   int i = 10, j = 20, sum =0,Sub=0,Mul = 0,Div = 0;

 

   public void init(){

   txtArea = new TextArea(10,20);

   txtArea.setEditable(false);

   add(txtArea,"center");

   Button b = new Button("Add");

   Button c = new Button("Subtract");

   Button d = new Button("Multiply");

   Button e = new Button("Divide");

   b.addActionListener(this);

   c.addActionListener(this);

   d.addActionListener(this);

   e.addActionListener(this);

 

   add(b);

   add(c);

   add(d);

   add(e);

   }

 

 

   public void actionPerformed(ActionEvent e){

   sum = i + j;

   txtArea.setText("");

   txtArea.append("i = "+ i + "\t" + "j = " + j + "\n");

   Button source = (Button)e.getSource();

   if(source.getLabel() == "Add"){

   txtArea.append("Sum : " + sum + "\n");

   }

   

   if(i >j){

   Sub = i - j;

   }

   else{

   Sub = j - i;

   }

   if(source.getLabel() == "Subtract"){

   txtArea.append("Sub : " + Sub + "\n");

   }

 

   Mul = i*j;

   if(source.getLabel() == "Multiply"){

   txtArea.append("Mul = " + Mul + "\n");

   }

 

   if(i > j){

   Div = i / j;

   }

   else{

   Div = j / i;

   }

 

   if(source.getLabel() == "Divide"){

   txtArea.append("Divide = " + Div);

   }

   }

 }

Here is the HTML code of the program :

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Comments:1

srj
September 21, 2011
plz give me output of this java listeners program

import java.awt.*; import java.awt.event.*; public class ls5 extends frame implements ActionListener { int cx=100,hx,hy; int i=1; boolean selected; MenuBar md; Menu sh; MenuItem rect,sqr,crcle; ls5(String s) { super(s); mb=new MenuBar(); setSize(300,300); setVisible(true); setLayout(new flowLyout(flowLayout(floeayout.LEFT))); ret=new MenuItem("RECTANGLE"); crcle=new MenuItem("CIRCLE"); sqr=new MenuItem("SQURE"); sh=new MenuItem("SELECT"); sh.add(rect); sh.add(sqr); sh.add(crcle); Mb.add(sh); setMenuBar(mb); rect.addActionListener(this); crcle.addACtionListner(this); sqr.addActionListner(this); addWindowListener(new windowAdaptor() { public class windowClosing(WindowEvent w) { System.exit(0); }; }); addKeyListener(new KeyAdaptor() { public void KeyPressed (KeyEvent ke) { if(ke.getKeyCode()==key.vk_DOWN) { cy+=10; repaint(); } if(ke.getKeyCode()==ke.vk_UP) { cx-=10; repaint(); } if(ke.getKeyCode()==ke.vk_LEFT) { cx-=10; repaint(); } if(ke.getKeyCode()==ke.vk_RIGHT) { cx+=10; repaint(); } } }); addMouseListener(new MouseAdaptor() { public void mousePressed(MouseEvent me) { int x=me.getx(); int y=me.gety(); if(x>c && (x<=(cx+80))&&(y>cy&&y<=(cy+60))) { selected=true; hx=x; hy=y; } else selected=false; } }); addMouseMotionListener(new MouseMotionAdaptor() { public class mouseDragged(MouseEvent me) { int x=me.getx(); int y=me.gety(); if(selected) { cx=cx+(x-hx); cy=cy+(y-hy); hx=x; hy=y; repaint(); } } }); } public void actionPreformed(ActionEvent e) { if(e.getSource()==rect) { c=1; setTittle("DragRectsngle"); repaint(); } if(e.getSource()==sqr) { i=2; setTittle("DragSquare"); repaint(); } if(e.gertSource()==crcle) { i=3; steTittle("Drag Cirle"); repaint(); } } public void paint() { if(i==1) { g.setColor(color.black); g.fillRect(cx,cy,80,60); } else if(i==2) { g.setcolor(color.black); g.fillRect(cx,cy,80,80); } else { g.setcolor(color.red); g.setOval(cx,cy,80,80); } } public static void main(String args[]) { ls5 apptt=new ls5("Drag Shape"); } }

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