Steps For Handling Events In JAVA

1. Create a class which extends Applet and implements 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 events 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 //step 1
{
    String message = " ";
    int mouseX = 0;
    int mouseY = 0;
    public void init() //step 2
        {
            addMouseListener(this); //step3
        }
    public void mouseEntered(MouseEvent m) //step4
        {
            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);
    }
}