public class Main extends Applet {

    private final int N = 3;
    private Ball[] balls = new Ball[N];
    private boolean flag = true;

    public void paint(Graphics g){
        g.setColor(Color.green);
        g.fillRect(0,0,this.getWidth(),this.getHeight());

        if(flag) {
        for(int i = 0; i < N; i++) {
            balls[i] = new Ball(this);
            balls[i].start();
        }
            try {
                Thread.sleep(0);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            flag = false;
        }

        g.dispose();
    }
}

public class Ball extends Thread {

    private Graphics2D g2d, buffGraphics;
    private Shape ball;
    private AffineTransform ballTransform = new AffineTransform();
    private BufferedImage bi;
    private Color color;
    private double width, height, deltaY, deltaX = 0.011;
    private final int rad = 20, diam = 2 * rad;

    Ball(Applet applet){
        bi = new BufferedImage(applet.getWidth(), applet.getHeight(), BufferedImage.TYPE_INT_ARGB);
        buffGraphics = bi.createGraphics();

        g2d = (Graphics2D)applet.getGraphics();
        g2d.setColor(Color.green);

        color = new Color((int)(Math.random() * 255),(int)(Math.random() * 255), (int)(Math.random() * 255) );
        ball = new Ellipse2D.Double(Math.random() * (applet.getWidth() - diam),
                Math.random() * (applet.getHeight() - diam),diam,diam);
        double h = 8 + Math.random() * 9;
        double temp = Math.random();
        double hX = PositiveOrNegative() * ((int)(temp * (h + 1)) == (int) h ? h : temp * h);
        double hY = PositiveOrNegative() * Math.sqrt(h * h - hX * hX);
        ballTransform.setToTranslation(hX, hY);

        deltaY = Math.abs(hY / (hX / deltaX));
        width = applet.getWidth();
        height = applet.getHeight();
    }

    private static int PositiveOrNegative()
    {
        return (Math.random() >= 0.5) ? 1 : -1;
    }

    @Override
    public void run() {
        buffGraphics.setColor(color);
        buffGraphics.fill(ball);
        g2d.drawImage(bi, 0 , 0, null);

        while(true) {
            try {
                if(ball.getBounds().x + diam == width || ball.getBounds().x == 0)
                    ballTransform.setToTranslation(-ballTransform.getTranslateX(), ballTransform.getTranslateY());
                else if(ball.getBounds().x + diam + ballTransform.getTranslateX() > width
                        && ballTransform.getTranslateX() / Math.abs(ballTransform.getTranslateX()) == 1) {
                    double hx = width - ball.getBounds().x - diam - 1,
                            hy = hx * Math.abs(ballTransform.getTranslateY()) / ballTransform.getTranslateX();
                    AffineTransform af1 = new AffineTransform();
                    af1.setToTranslation(hx,ballTransform.getTranslateY() / Math.abs(ballTransform.getTranslateY()) * hy);

                    Thread.sleep(30);
                    draw();

                    ballTransform.setToTranslation(-ballTransform.getTranslateX(), ballTransform.getTranslateY());
                }
                else if(ball.getBounds().x + ballTransform.getTranslateX() < 0
                        && ballTransform.getTranslateX() / Math.abs(ballTransform.getTranslateX()) == -1) {
                    double hx = ball.getBounds().x + 1,
                            hy = hx * Math.abs(ballTransform.getTranslateY()) / ballTransform.getTranslateX() * (-1);
                    AffineTransform af1 = new AffineTransform();
                    af1.setToTranslation( -hx,ballTransform.getTranslateY() / Math.abs(ballTransform.getTranslateY()) * hy);

                    Thread.sleep(30);
                    draw();

                    ballTransform.setToTranslation(-ballTransform.getTranslateX(), ballTransform.getTranslateY());
                }
                if(ball.getBounds().y + diam == height || ball.getBounds().y == 0)
                    ballTransform.setToTranslation(ballTransform.getTranslateX(), -ballTransform.getTranslateY());
                else if(ball.getBounds().y + diam + ballTransform.getTranslateY() > height
                        && ballTransform.getTranslateY() / Math.abs(ballTransform.getTranslateY()) == 1) {
                    double hy = height - ball.getBounds().y - diam - 1,
                            hx = hy * Math.abs(ballTransform.getTranslateX()) / ballTransform.getTranslateY();
                    AffineTransform af1 = new AffineTransform();
                    af1.setToTranslation(ballTransform.getTranslateX() / Math.abs(ballTransform.getTranslateX()) * hx, hy);

                    Thread.sleep(30);
                    draw();

                    ballTransform.setToTranslation(ballTransform.getTranslateX(), -ballTransform.getTranslateY());
                }
                else if(ball.getBounds().y + ballTransform.getTranslateY() < 0
                        && ballTransform.getTranslateY() / Math.abs(ballTransform.getTranslateY()) == -1) {
                    double hy = ball.getBounds().y + 1,
                            hx = hy * Math.abs(ballTransform.getTranslateX()) / ballTransform.getTranslateY() * (-1);
                    AffineTransform af1 = new AffineTransform();
                    af1.setToTranslation(ballTransform.getTranslateX() / Math.abs(ballTransform.getTranslateX()) * hx, -hy);

                    Thread.sleep(30);
                    draw();

                    ballTransform.setToTranslation(ballTransform.getTranslateX(), -ballTransform.getTranslateY());
                }

                Thread.sleep(60);
                draw();

                if(Math.abs(ballTransform.getTranslateX()) - deltaX <= 0 ||
                        Math.abs(ballTransform.getTranslateY()) - deltaY <= 0) break;
                ballTransform.setToTranslation(ballTransform.getTranslateX() / Math.abs(ballTransform.getTranslateX()) *
                                (Math.abs(ballTransform.getTranslateX()) - deltaX), ballTransform.getTranslateY() /
                        Math.abs(ballTransform.getTranslateY()) * (Math.abs(ballTransform.getTranslateY()) - deltaY));
                deltaX += 0.0015;
                deltaY = Math.abs(ballTransform.getTranslateY() / (ballTransform.getTranslateX() / deltaX));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        while(true) {
            try {
                Thread.sleep(60);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            g2d.drawImage(bi, 0, 0, null);
        }

    }

    private void draw(){
        g2d.fillOval(ball.getBounds().x-1,ball.getBounds().y-1,
                ball.getBounds().width+2, ball.getBounds().height+2);
        buffGraphics.setColor(Color.green);
        buffGraphics.setComposite(AlphaComposite.Clear);
        buffGraphics.fillOval(ball.getBounds().x-1,ball.getBounds().y-1,
                ball.getBounds().width+2, ball.getBounds().height+2);
        buffGraphics.setComposite(AlphaComposite.SrcOver);
        buffGraphics.setColor(color);

        ball = ballTransform.createTransformedShape(ball);
        buffGraphics.fill(ball);
        g2d.drawImage(bi, 0 , 0, null);
    }
}