A Simple Drawing Example

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Toolkit;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Serdar extends JPanel implements Runnable {
    private Random r = new Random();
    private static final long serialVersionUID = 1L;
    private ArrayList<Oval> list = new ArrayList<Oval>();

    public static void main(String args[])  {
        JFrame window = new JFrame("Water");
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Serdar serdar = new Serdar();
        Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
        dim.width -= 100; dim.height -= 100;
        serdar.setPreferredSize(dim);
        window.setContentPane(serdar);
        window.pack();
        window.setLocationRelativeTo(null);
        window.setVisible(true);
    }

    public Serdar() {
        super();
        Thread t = new Thread(this);
        t.start();
    }

    public void paint(Graphics g) {
        Iterator<Oval> it = list.iterator();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, getWidth(), getHeight());
        while( it.hasNext() ) {
            Oval o = it.next();
            if( o.r >= 50 ) {
                it.remove();
                continue;
            }
            g.setColor(o.c);
            o.r += 2;
            g.drawOval(o.x-o.r, o.y-o.r, 2*o.r, 2*o.r);
        }
    }

    public void run() {
        long time = 0;
        while(true) {
            repaint();
            time += 50;
            try {
                Thread.sleep(50);
            } catch (Exception e) {}
            if( time % 300 == 0 ) {
                Color c = new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255));
                list.add(new Oval(r.nextInt(getWidth()), r.nextInt(getHeight()), c));
            }
        }
    }

    private class Oval {
        public Oval(int x, int y, Color c) {
            this.x = x;
            this.y = y;
            this.c = c;
        }
        int x, y, r = 0;
        Color c;
    }
}