import java.applet.*;
import java.awt.*;
/* I know a ball isn't a Rectangle,
* but Rectangle provides alot of useful methods/properties :) */
class Ball extends Rectangle {
	public int xdir,ydir;
	public Color color;
	public Ball(int size) {
		xdir = 0;
		ydir = 0;
		this.width = size;
		this.height = size;
		color = Color.black;
	}
	public void collide(Ball b) {
		this.xdir*=-1;
		this.ydir*=-1;
		b.xdir*=-1;
		b.ydir*=-1;
	}
	public void check(Dimension d) {
		Rectangle r = new Rectangle(d.width,d.height);
		if (!r.contains(this)) {
			if (this.x < 0) this.x = 0;
			else if (this.x > r.width-this.width) this.x = r.width-this.width;
			if (this.y < 0) this.y = 0;
			else if (this.y > r.height-this.height) this.y = r.height-this.height;
			if (this.x == 0 || this.x == r.width-this.width) xdir*=-1;
			if (this.y == 0 || this.y == r.height-this.height) ydir*=-1;
		}
	}
	public void move() {
		this.translate(xdir,ydir);
	}
	public void paint(Graphics g) {
		g.setColor(color);
		g.fillOval(this.x,this.y,this.width,this.height);
	}
}
public class Bouncy extends Applet implements Runnable {
	Ball b[]; // ball for.. bouncing
	Dimension d;
	int w,h,collide;
	Image buffer;
	public void init() {
		d = getSize();
		w = d.width;
		h = d.height;
		collide = 0;
		buffer = createImage(w,h);
		// now we have to make the balls with random properties
		Color c[] = new Color[] {Color.red,Color.green,Color.blue,Color.cyan,Color.magenta,
					Color.black,Color.pink,Color.yellow};
		b = new Ball[rand(9)+1]; // at MOST 10 balls
		for (int j = 0;j < b.length;j++) {
			b[j] = new Ball(rand(20)+10); // diameter is at MOST 30
			b[j].x = rand(w-b[j].width); // random x
			b[j].y = rand(h-b[j].height); // random y
			b[j].xdir = rand(3)+2; // random x direction
			b[j].ydir = rand(3)+2; // random y direction
			b[j].color = c[rand(c.length-1)]; // random color
		}
		new Thread(this).start();
	}
	protected int rand(int r) {
		return (int)Math.round(Math.random()*r);
	}
	public void run() {
		// if you don't know about threads,
		// this will confuse the snot out of you.
		// so read up on threads!!
		while (true) {
			int j,n;
			// now we update each ball position
			for (j = 0;j < b.length;j++) {
				// make sure the ball is in the applet
				b[j].check(d);
				// move the ball
				b[j].move();
				// check for collisions...
				for (n = 0;n < b.length;n++) {
					if (n != j) { // no need to check current ball
						if (b[j].intersects(b[n])) {
							collide++;
							b[j].collide(b[n]); // adjust x/y directions
							// move both balls
							b[j].move();
							b[n].move();
						}
					}
				}
			}
			Graphics g = getGraphics();
			if (g != null) paint(g); // attempt active rendering
			else repaint(); // passive will work if active doesn't
			try {
				Thread.sleep(10);
			}
			catch (InterruptedException e) {
				break;
			}
		}
	}
	public void paint(Graphics g) {
		Graphics gfx = buffer.getGraphics();
		gfx.setColor(Color.white);
		gfx.fillRect(0,0,w,h);
		for (int j = 0;j < b.length;j++) {
			b[j].paint(gfx);
		}
		gfx.setColor(Color.black);
		FontMetrics f = gfx.getFontMetrics();
		gfx.drawString("Balls: "+b.length,10,h-f.getAscent());
		String s = "Collisions: "+collide;
		gfx.drawString(s,w-(f.stringWidth(s)+10),h-f.getAscent());
		gfx.drawRect(0,0,w-1,h-1);
		g.drawImage(buffer,0,0,null);
	}
	public void update(Graphics g) {
		paint(g);
	}
}