Rosnący okrąg - kod źródłowy

import java.applet.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class RosnacyOkrag extends Applet implements ActionListener, Runnable
{
	int szerokosc=1;
	int wysokosc=1;
	int i=0;
	Button rysuj = new Button("Rysuj");
	Button stop = new Button("Stop");
	private Thread watek;
	public void init()
	{
		setLayout(null);
		rysuj.setBounds(10, 0, 100, 20);
		stop.setBounds(10, 20, 100, 20);
		add(rysuj);
		add(stop);
		rysuj.addActionListener(this);
		stop.addActionListener(this);
	}

	public void paint(Graphics gDC)
	{
		Dimension rozmiarProgramu = this.getSize();
		int wspX = ((int)rozmiarProgramu.getWidth())/2;
		int wspY = ((int)rozmiarProgramu.getHeight())/2;
		gDC.drawOval(wspX-i, wspY-i, szerokosc+(2*i), wysokosc+(2*i));
	}
	
	public void actionPerformed(ActionEvent evt)
	{
		if(evt.getSource() == rysuj)
		{
			watek=new Thread(this); 
			watek.start();
		}
		else if(evt.getSource() == stop)
		{
			watek.stop();
		}
	}
	
	public void run() 
	{
		while(true) 
		{
			try 
			{ 
				Thread.currentThread().sleep(50);
				i++;
			} 
			catch (InterruptedException e ) 
			{}
			repaint();
		} 
	}
}