Help with a Java question for an exercise.

Question

Hi I am doing this exercise of a Blue J book for my Java course and I am completely stumped on this question.

Basically I have to 1 Only the bounce method in BallDemo needs to be changed. 2 The number of balls should be made a parameter of the method. 3 The balls should be given random sizes and placed in a row at the top of the canvas.

This is the code so far, I am using an ArrayList to store the number of balls the user specifies. I do not want the answer, but would appreciate it if someone would explain to me how to do this.

public class BallDemo
{ private Canvas myCanvas; private ArrayList<BouncingBall>balls; private Random ballSize;

/**
 * Create a BallDemo object. Creates a fresh canvas and makes it visible.
 */
public BallDemo()
{
    myCanvas = new Canvas("Ball Demo", 600, 500);
    balls = new ArrayList<BouncingBall>();
    ballSize = new Random();
}

/**
 * Simulate two bouncing balls
 */
public void bounce(BouncingBall ball)
{
    int ground = 400;   // position of the ground line

    myCanvas.setVisible(true);

    // draw the ground
    myCanvas.drawLine(50, ground, 550, ground);

    balls.add(ball);
    //Trying to implement the method

    // crate and show the balls
    BouncingBall ball = new BouncingBall(50, 50, 16, Color.BLUE, ground, myCanvas);
    ball.draw();
    BouncingBall ball2 = new BouncingBall(70, 80, 20, Color.RED, ground, myCanvas);
    ball2.draw();
    BouncingBall ball3 = new BouncingBall(90, 110, 24, Color.YELLOW, ground, myCanvas);
    ball3.draw();
    BouncingBall ball4 = new BouncingBall(110, 140, 28, Color.GREEN, ground, myCanvas);
    ball4.draw();

    // make them bounce
    boolean finished =  false;
    while(!finished) {
        myCanvas.wait(50);           // small delay
        ball.move();
        ball2.move();
        ball3.move();
        ball4.move();
        // stop once ball has travelled a certain distance on x axis
        if(ball.getXPosition() >= 600 && ball2.getXPosition() >= 600 && ball3.getXPosition() >= 600 
        && ball4.getXPosition() >= 600) {
            finished = true;
        }
    }
}

}

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Yasir Khan

Yasir Khan

Help with a Java question for an exercise.