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

public class MyBall extends Applet implements Runnable {
	Thread th;
	
	Ball  ballA = new Ball(5, 10, 10, 1, 1, Color.BLUE); 
	Ball  ballB = new Ball(5, 10,190, 1,-1, Color.RED); 	
	Ball  ballC = new Ball(5,190, 10,-1, 1, Color.GREEN);
	Ball  ballD = new Ball(5,190,190,-1,-1, Color.BLACK);;
	public void start() {
			th = new Thread(this);
			th.start();
	}
	
	public void run() {
		while (true) {
			repaint();    // paint() を呼び出す
			ballA.move();
			ballB.move();			
			ballC.move();
			ballD.move();
			try {
				th.sleep(10);
			
			}
			catch(InterruptedException e) {}    // 例外処理はしない
	
		}
	}
	
	public void paint(Graphics g) {	
		ballA.display(g);     // ballA の display メソッドを呼び出す
		ballB.display(g); 				
		ballC.display(g);
		ballD.display(g);
	}
	
}

// クラスの設計
class Ball {
	Color c;
	int size, x, y, xDelta, yDelta;
	
	Ball (int size, int x, int y, int xDelta, int yDelta, Color c) {
		this.size = size;
		this.x = x;
		this.y = y;
		this.xDelta = xDelta;
		this.yDelta = yDelta;
		this.c = c;
	}
	// メソッド
	public void move() {
		if (x + size >= 200) {
			xDelta = - xDelta;
		}
		if (y + size >= 200) {
			yDelta = - yDelta;
		}
		if (x < 0) {
			xDelta = (int) Math.round(Math.floor(Math.random()*20));
		}
		if (y < 0) {
			yDelta = (int) Math.round(Math.floor(Math.random()*20));
		}
			
		
		
		
		x = x + xDelta;
		y = y + yDelta;
	}
	
	public void display(Graphics g) {
		g.setColor(c);
		g.fillOval(x, y, size, size);
	};
	}