Collision detection

import java.awt.*;
import java.applet.*;

public class col extends Applet implements Runnable
{
    Image Buffer;
    Graphics gBuffer;
    int x, y;
    boolean mouseInside, collide;
    Rectangle r1, r2;

    public void init()
    {
        Buffer=createImage(size().width,size().height);
        gBuffer=Buffer.getGraphics();
        r1=new Rectangle(110,115,60,50);
        r2=new Rectangle(40,100);
    }

    public void drawStuff()
    {
        gBuffer.setColor(Color.white);

        gBuffer.fillRect(0,0,size().width,size().height);

        gBuffer.setColor(Color.red);
        gBuffer.fillOval(r1.x, r1.y, r1.width, r1.height);

        gBuffer.setColor(Color.blue);

        gBuffer.fillRect(r2.x, r2.y, r2.width, r2.height);

        gBuffer.setColor(Color.black);

        if(collide)
            r1.y = 0;
    }

    public boolean mouseEnter(Event evt,int x,int y)
    {
        mouseInside=true;
        repaint();

        return true;
    }

    public boolean mouseExit(Event evt,int x,int y)
    {
        mouseInside=false ;
        repaint();

        return true;
    }

    public boolean mouseMove(Event evt,int x,int y)
    {
        this.x=x;
        this.y=y;

        r2.move(x-r2.width/2, y-r2.height/2);


        collide=r1.intersects(r2);

        drawStuff();

        repaint();
        return true;
    }

    public void update(Graphics g)
    {
        paint(g);
    }

    public void paint(Graphics g)
    {
        drawStuff();
        g.drawImage (Buffer,0,0, this);
    }

public void start(){
      		   Thread tbal = new Thread (this);
                   tbal.start(); 
                   }
public void run (){
      		while (true){    r1.x++; repaint();
            			try{
                  		   Thread.sleep (20);
			           }
            			   catch (InterruptedException ex){}
			    repaint();
                            } 
                  }


}