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 :
<HTML>
<BODY>
<APPLET CODE
="EventListeners" WIDTH="800"
HEIGHT="500"></APPLET>
</BODY>
</HTML> |
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