import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Random;

public class BouncingBallsWithRebound			// this class is the same as BouncingBalls but adds to actionPerformed a little code, so the comments here focus just on the changes
{
	public static void main(String[] args)
	{
		JFrame frame=new JFrame();
		frame.setSize(540,540);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		GraphicsPanel gp=new GraphicsPanel();
		frame.add(gp);
		frame.setVisible(true);
	}
	
	public static class GraphicsPanel extends JPanel implements ActionListener
	{
		private BouncingBall[] balls;
		private int number;
		private Random generator;
		
		public GraphicsPanel()
		{
			number=25;
			generator=new Random();
			balls=new BouncingBall[25];
			for(int i=0;i<number;i++)
				balls[i]=new BouncingBall(500,500,generator);
			Timer t=new Timer(30,this);
			t.start();
		}
		
		public void actionPerformed(ActionEvent e)
		{
			for(int i=0;i<number;i++)
			{
				balls[i].move();							 	// now that balls[i] has been moved, see if it collides with any other of the balls
				for(int j=0;j<number;j++)						// search through all of the balls
					if(i!=j&&balls[i].collide(balls[j]))		// if the other ball is not this ball (i!=j) see if they collide
					{
						balls[i].rebound();						// if they collide, tell each ball to rebound itself (which gives it a random new motion)
						balls[j].rebound();						//     we could have instead rebounded only one or implemented rebound differently
					}
			}
			repaint();
		}
		
		public void paintComponent(Graphics g)
		{
			super.paintComponent(g);
			g.setColor(Color.white);
			g.fillRect(0,0,540,540);
			for(int i=0;i<number;i++)
				balls[i].draw(g);
		}
	}
}