keylistener - java

KeyListener in Java

  • The following program that implements the KeyListener interface. When executed, the Java code will show a very simple Swing Graphical User Interface.
  • The GUI is made up of a JFrame which contains two JTextAreas. The first, feedbackText JTextArea, is placed inside a JScrollPane and is used to display text generating by the KeyListener events.
  • The JScrollPane allows the user to see all the lines of text generated by the KeyListener events.
  • This JTextArea has the focus and will generate KeyListener events as the user types into it. By default. the inputArea JTextArea will have the focus when the JFrame appears.
  • The KeyListener interface could have been implemented as a separate class, or extending the JFrame, but in this instance using an anonymous inner class makes the most sense.
  • The keyPressed method is called when a user presses down on a key, and the keyReleased method is called when a key is released. The keyTyped method is called when a character key is typed into the inputText JTextArea.


import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;

//Here's a class for a simple GUI that uses a JFrame
//to hold to JTextAreas - one will listen for the key events
//and the other will sit inside a JScrollPane providing feedback
//about the KeyListener events being triggered

public class KeyListenerExample {
    JTextArea inputText;
    JTextArea feedbackText;

     //Note: Typically the main method will be in a
    //separate class. As this is a simple one class
    //example it's all in the one class.
    public static void main(String[] args) {

         //Use the event dispatch thread for Swing components
         EventQueue.invokeLater(new Runnable()
             public void run()
                 new KeyListenerExample();         
    public KeyListenerExample()
        JFrame guiFrame = new JFrame();
        //make sure the program exits when the frame closes
        guiFrame.setTitle("Creating a Table Example");
        //This will center the JFrame in the middle of the screen
        //This JTextArea is used to display information about
        //the keylistener events. It's place in a JScrollPane
        //to allow the scrolling through all the events triggered
        feedbackText = new JTextArea();
        JScrollPane scrollText = new JScrollPane(feedbackText);
        //This JTextArea will trigger the KeyListener events as
        //long as it hold the focus
        inputText = new JTextArea();
        //The KeyListener interface is implemented as an anonymous
        //inner class using the addKeyListener method.
        inputText.addKeyListener(new KeyListener()
              //When any key is pressed and released then the 
              //keyPressed and keyReleased methods are called respectively.
              //The keyTyped method is called when a valid character is typed.
              //The getKeyChar returns the character for the key used. If the key
              //is a modifier key (e.g., SHIFT, CTRL) or action key (e.g., DELETE, ENTER)
              //then the character will be a undefined symbol.
              public void keyPressed(KeyEvent e)
                  feedbackText.append("Key Pressed: " + e.getKeyChar() + "\n");
              public void keyReleased(KeyEvent e)
                  feedbackText.append("Key Released: " + e.getKeyChar() + "\n");
              public void keyTyped(KeyEvent e)
                  //The getKeyModifiers method is a handy
                  //way to get a String representing the
                  //modifier key.
                  feedbackText.append("Key Typed: " + e.getKeyChar() + " " + KeyEvent.getKeyModifiersText(e.getModifiers()) + "\n");
        guiFrame.add(inputText, BorderLayout.NORTH);
        guiFrame.add(scrollText, BorderLayout.CENTER);

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