SWING - FocusListener Interface

The interface FocusListener is used  for receiving keyboard focus events. The class that processes focus events needs to implements this interface.
Following is the declaration for java.awt.event.FocusListener interface −
public interface FocusListener
extends EventListener

void focusGained(FocusEvent e)
Invoked when a component gains the keyboard focus.
void focusLost(FocusEvent e)
Invoked when a component loses the keyboard focus.
This class inherits methods from the following interfaces −
java.awt.event.EventListener
Create the following Java program using any editor of your choice in say D:/ > SWING > com > tutorialspoint > gui >
SwingListenerDemo.java
package com.tutorialspoint.gui;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class SwingListenerDemo {
   private JFrame mainFrame;
   private JLabel headerLabel;
   private JLabel statusLabel;
   private JPanel controlPanel;
   
   public SwingListenerDemo(){
      prepareGUI();
   }
   public static void main(String[] args){
      SwingListenerDemo  swingListenerDemo = new SwingListenerDemo();  
      swingListenerDemo.showFocusListenerDemo();
   }
   private void prepareGUI(){
      mainFrame = new JFrame("Java SWING Examples");
      mainFrame.setSize(400,400);
      mainFrame.setLayout(new GridLayout(3, 1));

      headerLabel = new JLabel("",JLabel.CENTER );
      statusLabel = new JLabel("",JLabel.CENTER);        
      statusLabel.setSize(350,100);
      
      mainFrame.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent windowEvent){
            System.exit(0);
         }        
      });    
      controlPanel = new JPanel();
      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");      
      JButton okButton = new JButton("OK");
      JButton cancelButton = new JButton("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 the command prompt. Go to D:/ > SWING and type the following command.
D:\SWING>javac com\tutorialspoint\gui\SwingListenerDemo.java

If no error occurs, it means the compilation is successful. Run the program using the following command.
D:\SWING>java com.tutorialspoint.gui.SwingListenerDemo

Verify the following output.

    30 Lectures 
     3.5 hours 

 Pranjal Srivastava

    13 Lectures 
     1 hours 

 Pranjal Srivastava

    25 Lectures 
     4.5 hours 

 Emenwa Global, Ejike IfeanyiChukwu

    14 Lectures 
     1.5 hours 

 Travis Rose

    14 Lectures 
     1 hours 

 Travis Rose
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