import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JPanel;
import javax.swing.Timer;

@SuppressWarnings("serial")
public class ui extends JPanel implements ActionListener {
    public int x, y;
    public Screen() {
        x = y = 10;
        Timer timer = new Timer(5, this);
        timer.start();
    }

    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D gc = (Graphics2D) g;

        gc.setPaint(Color.BLUE);
        gc.fillRect(x, y, 100, 100);
        Toolkit.getDefaultToolkit().sync();
        g.dispose();
    }

    public void actionPerformed(ActionEvent e) {
        x += 1;
        y += 1;
        if (x>800 && y>600)
            x = y = 0;
        repaint();
    }
}