Java GUI >> Basic Animation (bounce back logic added)

gistfile1.java

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

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class MyGUI extends JPanel implements ActionListener 
{
  Timer tm = new Timer(5, this); //this refers to ActionListener's event?
	int x=0,y=0,vel=1;
	
	public void paintComponent(Graphics g) 
	{
		/*If your paintComponent() method wants to clear the background area all it has
		to do is call the super paintComponent() method and make the component opaque when it is initialized.*/
		super.paintComponent(g); 
		g.setColor(Color.RED);
		g.fillRect(x, y, 50, 30);
		
		tm.start(); //this starts ActionEvent after 5 miliseconds
		
	}
	     
	public static void main(String[] args)
       {
    	   MyGUI gui=new MyGUI();
    	   JFrame frame = new JFrame();
    	   frame.setTitle("Basic Animation");
    	   frame.setSize(500,500);
    	   frame.setVisible(true);
    	   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    	   frame.add(gui);
    	   
    	   
    	   
       }

	public void actionPerformed(ActionEvent arg0)
	{
		if(x<0 || x>450) //bounce it back style!!!
			vel=-vel;
		x+=vel;
		y+=vel;
		repaint();
	}
     
     
 }