EVENT HANDLING Presented by - PowerPoint Presentation

Slide1

EVENT HANDLING Presented byMr. G. M. KrishnapkshiAssistant ProfessorDepartment of Computer Science and IT.Deogiri College, Aurangabad

DEOGIRI COLLEGE,AURANGABADEVENT HANDLING By-G.M. KrishnapakshiSUBJECT-JAVA

Event handlingevent:- 1) An event is an object that describe a state change in a source. 2) Some of the activities that causes event to be generated are: i) Pressing a Button. ii) Entering a character through Key Board. iii) Selecting an item form a list etc.

Event delegation modelEvent delegation model means Events which are generated by Event Source for Event Receiver are processed by Event ListenerThere are two main types in Event Delegation Model 1) Event source 2) Event Listener

Receiver

Listener

Source

Event

Event

1) EVENT SOURCE i) A source is an object that generates an event. ii) Event source is an object through which an action is to be generated . iii) Some general Event Source are 1) Button, CheckBox 2) List, MenusItem etc….. iv) Here is a general form for adding a listener to an event source:

public void addTypeListener(TypeEvent e)

* ‘Type’ is the name of the event.

* ‘e’ is the reference of the event listener

2) Event listener i) A listener is an object that is notified when an event occurs. ii) Event Listener are the object which is bind with a event sources and it carried out the event which was generated by Event Sources. iii) Example: MouseListener, KeyListner. iv)

MouseMotionListner interface

define two events.

a) When mouse is dragged.

b) When mouse is moved

v) For implementing event listener we have to import the following statement

import java.awt.event.*;

Example of event handlingimport java.applet.Applet;import java.awt.*;import java.awt.event.*;public class TextFiled extends Applet implements ActionListener{ int n,square; Label ll=new Label("Numbers"); TextField t=new TextField(5);

Button b=new Button(“Square");

public void init() { add(ll); add(t); add(b); b.addActionListener(this); } public void paint(Graphics g) { g.drawString("Square is="+square,20,50); }

public void actionPerformed(ActionEvent ae)

{

n=Integer.parseInt(t.getText());

square=n*n;

repaint();

}

}

Output:

Any question?

Thank you!!