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

class Ball {
       int x = 7, xChange = 7;
       int y = 2, yChange = 2;
       int diameter = 10;
       Color color = Color.RED;
       
       Ball() {
           
       }
       
       Ball(int x, int y, int xChange, int yChange, int diameter, Color color) {
           this.x = x;
           this.y = y;
           this.xChange = xChange;
           this.yChange = yChange;
           this.diameter = diameter;
           this.color = color;
       }
    
}

class Bounds {
        int LeftX = 50, RightX = 150;
        int TopY = 50, BottomY = 150;
}

public class BallBox5  extends Applet {
       
        int numBalls = 5;
        Ball [] balls = new Ball[5];
     
        
        Bounds box;
        
        public void init() {
            box = new Bounds();
            balls[0] = new Ball();
            balls[1] = new Ball(7, 2, 3, 5, 12, Color.GREEN);
            balls[2] = new Ball(7, 2, 4, -1, 8, Color.BLUE);
            balls[3] = new Ball(7, 2, 5, 2, 9, Color.CYAN);
            balls[4] = new Ball(7, 2, 3, -4, 11, Color.MAGENTA);
       
        }
        
        private void eraseBall(Graphics g, Ball ball) {
            g.fillOval(ball.x + box.LeftX, ball.y + box.TopY, ball.diameter, ball.diameter);
        }
        
        private void moveAndDrawBall(Graphics g, Ball ball) {
            int width = box.RightX - box.LeftX;
            int height = box.BottomY - box.TopY;
            if (ball.x <= 0) ball.xChange = -ball.xChange;
            if (ball.x >= width) ball.xChange = -ball.xChange;
                           
                if (ball.y <= 0) ball.yChange = -ball.yChange;
                if (ball.y >= height) ball.yChange = -ball.yChange;
                ball.x = ball.x + ball.xChange;
                ball.y = ball.y + ball.yChange;
                g.setColor(ball.color);
                g.fillOval(ball.x + box.LeftX, ball.y + box.TopY, ball.diameter, ball.diameter);
            
        }

        
        public void paint(Graphics g) {
            g.drawRect(box.LeftX, box.TopY, box.RightX - box.LeftX,
                    box.BottomY - box.TopY);
            for (int n = 1; n < 300; n++) {
                Color backgroundColor = getBackground();
                g.setColor(backgroundColor);
                
                for (int i = 0; i < numBalls; i++) {
                    eraseBall(g, balls[i]);
                }
                
                for (int i = 0; i < numBalls; i++) {
                    moveAndDrawBall(g, balls[i]);
                }
               
         
                try {
                    Thread.sleep(50);
                   
                }
                catch (InterruptedException e) {
                    System.err.println("sleep exception");
                }
            }
        }
}