Reputation: 8578
public class MyPanel extends JPanel implements KeyListener {
private char c = 'e';
public MyPanel() {
this.setPreferredSize(new Dimension(500,500));
addKeyListener(this);
}
public void paintComponent(Graphics g) {
super.repaint();
g.drawString("the key that pressed is" + c, 250,250);
}
public void keyPressed(KeyEvent e) {
c=e.getKeyChar();
repaint();
}
public void keyReleased(KeyEvent e) {
}
public void keyTyped(KeyEvent e) {
c=e.getKeyChar();
repaint();
}
public static void main(String[] s) {
JFrame f=new JFrame();
f.getContentPane().add(new MyPanel());
f.pack();
f.setVisible(true);
}
}
I tried reading this yet didnt mange to understand how to simply implement a KeyListener. so what do i need to change for this to work?
Upvotes: 6
Views: 55308
Reputation: 421290
Here are the reasons why it doesn't work:
The JPanel
does not have the keyboard focus. (The frame has it.) You probably want to requestFocus
when the panel is added to the screen.
You need to call repaint
when the graphic should change.
You mustn't call repaint
in the paintComponent
method.
You need to clear the drawing area before drawing the string again (otherwise all characters will end up on top of each other).
Here's a complete working example:
class MyPanel extends JPanel implements KeyListener {
private char c = 'e';
public MyPanel() {
this.setPreferredSize(new Dimension(500, 500));
addKeyListener(this);
}
public void addNotify() {
super.addNotify();
requestFocus();
}
public void paintComponent(Graphics g) {
g.clearRect(0, 0, getWidth(), getHeight());
g.drawString("the key that pressed is " + c, 250, 250);
}
public void keyPressed(KeyEvent e) { }
public void keyReleased(KeyEvent e) { }
public void keyTyped(KeyEvent e) {
c = e.getKeyChar();
repaint();
}
public static void main(String[] s) {
JFrame f = new JFrame();
f.getContentPane().add(new MyPanel());
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.pack();
f.setVisible(true);
}
}
Oh, and you may want to add f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)
to make the application terminate when you close the window. :-)
Upvotes: 13