In this example we are going to see how you can use a KeyListener in Java, in order to monitor key events that take place in your applications. This is particularly useful when you want to add some key functionality to your app and it’s very important you want to monitor that has a very intensive keyboard activity.
Basically, to use a KeyListener in Java you have to:
- Create a new
KeyListenerinstance. - Override the methods that correspond to the key events you want to monitor e.g
keyPressed,keyReleased,keyTyped. - Create a
JTextFieldcomponent - Use it’s
addKeyListenermethod to add to it theKeyListeneryou’ve created. - Create a
MouseAdapterinstance. - Override
mousePressedmethod to monitor the mouse button activities.
Let’s take a closer look at the code snippet that follows:
package com.javacodegeeks.snippets.desktop;
import java.awt.AWTEventMulticaster;
import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JFrame;
import javax.swing.JTextField;
public class KeyTest {
public static void main(String args[]) {
JFrame jfr = new JFrame("Key Text Sample");
KeyTextComponent keyTtx = new KeyTextComponent();
final JTextField jtf = new JTextField();
ActionListener actListener = new ActionListener() {
@Override
public void actionPerformed(ActionEvent actionEvent) {
String keyText = actionEvent.getActionCommand();
jtf.setText(keyText);
}
};
keyTtx.addActionListener(actListener);
Container cp = jfr.getContentPane();
cp.add(keyTtx, BorderLayout.CENTER);
cp.add(jtf, BorderLayout.SOUTH);
jfr.setSize(200, 200);
jfr.setVisible(true);
}
}
class KeyTextComponent extends Canvas {
private ActionListener listnerList = null;
public KeyTextComponent() {
setBackground(Color.BLACK);
KeyListener keyListener = new KeyAdapter() {
@Override
public void keyPressed(KeyEvent keyEvent) {
if (listnerList != null) {
int key = keyEvent.getKeyCode();
String keystr = KeyEvent.getKeyText(key);
ActionEvent aEvent = new ActionEvent(this,
ActionEvent.ACTION_PERFORMED, keystr);
listnerList.actionPerformed(aEvent);
}
}
};
MouseListener mListner = new MouseAdapter() {
@Override
public void mousePressed(MouseEvent mEvent) {
requestFocus();
}
};
addKeyListener(keyListener);
addMouseListener(mListner);
}
public void addActionListener(ActionListener actionListn) {
listnerList = AWTEventMulticaster.add(listnerList,
actionListn);
}
public void removeActionListener(ActionListener actionListn) {
listnerList = AWTEventMulticaster.remove(listnerList,
actionListn);
}
@Override
public boolean isFocusTraversable() {
return true;
}
}
This was an example on how to work with the KeyListener component.
