AWT FocusListener Interface

  • Post author:
  • Post category:AWT
  • Post comments:0 Comments
 FocusListener

Introduction

The interface FocusListener is used for receiving keyboard focus events. The class that process focus events needs to implements this interface.

Class declaration

Following is the declaration for java.awt.event.FocusListener interface:

public interface FocusListener
extends EventListener

Interface methods

S.N.Method & Description
1void focusGained(FocusEvent e)Invoked when a component gains the keyboard focus.
2void focusLost(FocusEvent e)Invoked when a component loses the keyboard focus.

Methods inherited

This class inherits methods from the following interfaces:

  • java.awt.event.EventListener

FocusListener Example

Create the following java program using any editor of your choice in say D:/ > AWT > com > adglob> gui >AwtListenerDemo.java

package com.adglob.gui;

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

public class AwtListenerDemo {
   private Frame mainFrame;
   private Label headerLabel;
   private Label statusLabel;
   private Panel controlPanel;

   public AwtListenerDemo(){
      prepareGUI();
   }

   public static void main(String[] args){
      AwtListenerDemo  awtListenerDemo = new AwtListenerDemo();  
      awtListenerDemo.showFocusListenerDemo();
   }

   private void prepareGUI(){
      mainFrame = new Frame("Java AWT Examples");
      mainFrame.setSize(400,400);
      mainFrame.setLayout(new GridLayout(3, 1));
      mainFrame.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent windowEvent){
            System.exit(0);
         }        
      });    
   
      headerLabel = new Label();
      headerLabel.setAlignment(Label.CENTER);
      statusLabel = new Label();        
      statusLabel.setAlignment(Label.CENTER);
      statusLabel.setSize(350,100);

      controlPanel = new Panel();
      controlPanel.setLayout(new FlowLayout());

      mainFrame.add(headerLabel);
      mainFrame.add(controlPanel);
      mainFrame.add(statusLabel);
      mainFrame.setVisible(true);  
   }

       
   private void showFocusListenerDemo(){

      headerLabel.setText("Listener in action: FocusListener");      

      Button okButton = new Button("OK");
      Button cancelButton = new Button("Cancel");
      okButton.addFocusListener(new CustomFocusListener());  
      cancelButton.addFocusListener(new CustomFocusListener());  

      controlPanel.add(okButton);
      controlPanel.add(cancelButton);     
      mainFrame.setVisible(true);  
   }

   class CustomFocusListener implements FocusListener{
      public void focusGained(FocusEvent e) {
         statusLabel.setText(statusLabel.getText() 
         + e.getComponent().getClass().getSimpleName() + " gained focus. ");
      }

      public void focusLost(FocusEvent e) {
         statusLabel.setText(statusLabel.getText() 
         + e.getComponent().getClass().getSimpleName() + " lost focus. ");
      }
   }
}

Compile the program using command prompt. Go to D:/ > AWT and type the following command.

D:\AWT>javac com\adglob\gui\AwtListenerDemo.java

If no error comes that means compilation is successful. Run the program using following command.

D:\AWT>java com.adglob.gui.AwtListenerDemo

Verify the following output

 FocusListener

Previous Page:-Click Here

Leave a Reply