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AWT KeyListener Interface

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KeyListener

In this topic, we will discuss KeyListener in the AWT interface.

The class which processes the KeyEvent should implement this interface.The object of that class must be registered with a component. The object can be registered using the addKeyListener() method.

Interface declaration

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

public interface KeyListener
   extends EventListener

Interface methods

S.N.Method & Description
1void keyPressed(KeyEvent e)Invoked when a key has been pressed.
2void keyReleased(KeyEvent e)Invoked when a key has been released.
3void keyTyped(KeyEvent e)Invoked when a key has been typed.

Methods inherited

This interface inherits methods from the following interfaces:

  • java.awt.EventListener

KeyListener 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;
   private TextField textField;
   
   public AwtListenerDemo(){
      prepareGUI();
   }

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

   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 showKeyListenerDemo(){
      headerLabel.setText("Listener in action: KeyListener");      

      textField  = new TextField(10);

      textField.addKeyListener(new CustomKeyListener());
      Button okButton = new Button("OK");
      okButton.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            statusLabel.setText("Entered text: " + textField.getText());                
         }
      });

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

   class CustomKeyListener implements KeyListener{
      public void keyTyped(KeyEvent e) {           
      }

      public void keyPressed(KeyEvent e) {
         if(e.getKeyCode() == KeyEvent.VK_ENTER){
            statusLabel.setText("Entered text: " + textField.getText());
         }
      }

      public void keyReleased(KeyEvent e) {            
      }    
   } 
}

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

KeyListener

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