by Dinesh Thakur Category: Swing

Key events occur when a key is pressed, released or typed on a component. Objects representing key events are created from KeyEvent class. The corresponding listener interface for KeyEvent class is KeyListener. Each listener for KeyEvent should implement the KeyListener interface. The KeyListener interface defines three methods.

public void keyTyped(KeyEvent e)

public void keyPressed(KeyEvent t e)

public void keyReleased(KeyEvent e)

 Demonstrate the event handling mechanism using KeyListener interface

import javax.swing.*;

import java.awt.event.*;
import java.awt.*;
class KeyListenerExample extends JFrame implements KeyListener
{
       JTextField data;
       JTextArea  txtData;
       String s="";
       KeyListenerExample()
       {
         JPanel panell = new JPanel(new FlowLayout());
         JPanel panel2 = new JPanel(new FlowLayout());
         data = new JTextField(20);
         txtData = new JTextArea(20,30);
         data.addKeyListener(this);
         panell.add(data);
         panel2.add(txtData);
         add(panell,BorderLayout.NORTH);
         add(panel2,BorderLayout.CENTER);
       }
      public void keyTyped(KeyEvent e)
      {
        s  += "\n KeyTyped = " + String.valueOf(e.getKeyChar());
        System.out.println(s);
        txtData.setText(s);
      }
     public void keyPressed(KeyEvent e)
     {
       s += "\n KeyPressed = " +String.valueOf(e.getKeyCode());
       System.out.println(s);
       txtData.setText(s);
     }
     public void keyReleased(KeyEvent e)
     {
       s += "\n KeyReleased = " +String.valueOf(e.getKeyCode());
       System.out.println(s);
       txtData.setText(s);
     }
   }
   class KeyListenerJavaExample
   {
      public static void main(String[] args)
      {
         KeyListenerExample frame = new KeyListenerExample();
         frame.setTitle("KeyListener Java Example");
         frame.setBounds(100,200,350,300);
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         frame.setVisible(true);
     }
   }

KeyListener in Java Swing Example

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