How to create an event listener in Applet in Java

Problem Description

How to create an event listener in Applet?

Solution

Following example demonstrates how to create a basic Applet having buttons to add & subtract two nos. Methods used here are addActionListener() to listen to an event(click on a button) & Button() construxtor to create a button.

import java.applet.*;
import java.awt.event.*;
import java.awt.*;

public class EventListeners extends Applet implements ActionListener {
   TextArea txtArea;
   String Add, Subtract;
   int i = 10, j = 20, sum = 0, Sub = 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");
      b.addActionListener(this);
      c.addActionListener(this);
      add(b);
      add(c);
   }
   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");
      }
   }
}

Result

The above code sample will produce the following result in a java enabled web browser.

View in Browser.