Rectangle X axis move issue

Question

I was just doing random stuff with GUI and I came to this issue.When I press right arrow key, rectangle really moves on X axis, but distance moved is not constant.It's raising pretty fast and rectangle does after each press bigger moves.In my recent code line X=X+1 seemed to work pretty fine.Here's my code:

import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.*;


public class Buffer extends JPanel implements KeyListener{
public static JFrame frame;
public int x;

public void paintComponent(Graphics g){
    super.paintComponent(g);
    g.setColor(Color.red);
    g.fillRect(x,0,20,20);
    frame.addKeyListener(this);
}




public static void main(String args[]){
    Buffer z=new Buffer();

    frame=new JFrame();
    frame.setSize(500,500);
    frame.setVisible(true);
    frame.setFocusable(true);
    frame.add(z);
}
@Override
public void keyPressed(KeyEvent e) {
    if(e.getKeyCode()==KeyEvent.VK_RIGHT){
        x=x+1;
        repaint();
    }

}
    }

Answer 1

Remove the following line from public void paintComponent(Graphics g)

frame.addKeyListener(this);

and add the following line to public static void main(String args[])

frame.addKeyListener(z);

The problem was that after every repaint(); through the keyPressed method, the paintComponent method added a new KeyListener to your frame.
But if you have several KeyListeners, every Listener will invoke the keyPressed method for the same event. So if you have 5 Listeners and you press the right arrow once, the keyPressed method is invoked five times and x is incremented by five.
That meant that the rectangle moved with every hit of the right arrow a bit faster.