Steps For Handling Events In JAVA

This blog show show the steps for handling events in JAVA.

1. Create a class that extends Applet and implements an interface.

 

class<name> extends Applets implements <interface>

 

Class Skey extends Applet implements MouseListener

 

There are different Interfaces for different events i.e.for keyboard->KeyListner, for Mouse->MouseListner/MouseMotionListner etc.

 

2. Initialize applet by init method.

 

init() { }

 

3. Add or Register the listener to source for receiving notification. Each type of event has its own listener.

add TypeListener(TypeListener);
addMouseListener(this);

4. Implement the method to receive and process these notifications.

public void method(eventclass obj){}
public void mouseEntered(MouseEvent m){}
public void mousePressed(MouseEvent m){}
public void mouseClicked(MouseEvent m){}
public void mouseExited(MouseEvent m){}
public void mouseReleased(MouseEvent m){}

Components of Event Handling are the following:

• Event Source: ex.Button, CheckBox
• EventListener Interface: MouseListener
• Event classes: Mouse Event
• Methods of EventListener Interface: mouseEntered(),mousePressed(),mouseReleased(),mouseExited(),mouseClicked()

Ex.Program:

package proj2;
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class One extends Applet implements MouseListener {
 String message = " ";
 int mouseX = 0;
 int mouseY = 0;
 public void init() {
  addMouseListener(this);
 }
 public void mouseEntered(MouseEvent m) {
  mouseX = m.getX();
  mouseY = m.getY();
  repaint();
 }
 public void mouseExited(MouseEvent m) {
  mouseX = m.getX();
  mouseY = m.getY();
  repaint();
 }
 public void mouseClicked(MouseEvent m) {
  message = "Mouse Clicked at :";
  mouseX = m.getX();
  mouseY = m.getY();
  repaint();
 }
 public void mousePressed(MouseEvent m) {
  message = "Mouse button is pressed at :";
  mouseX = m.getX();
  mouseY = m.getY();
  repaint();
 }
 public void mouseReleased(MouseEvent m) {
  message = " mouse released";
  mouseX = m.getX();
  mouseY = m.getY();
  repaint();
 }
 public void paint(Graphics g) {
  g.drawString(message, mouseX, mouseY);
 }
}