Java: Ball Collision with Frame

Question

Not knowing how to do this is killing me. I currently have a frame with a ball which moves diagonally downwards and right, when it collides with the edge of the frame, it needs to bounce. The bounce part I can work out myself after, what I need help with is the ball knowing when it hits the edge of the frame.

Main:

class ControlledBall extends JPanel {
private int x = 70;
private int y = 30;
private boolean yes = true;

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g;
    g2.setColor(Color.BLUE);
    Ellipse2D.Double ball = new Ellipse2D.Double(x,y,50,50);
    g2.draw(ball);
    g2.fill(ball);
}
public void moveRight(int d) {x = x + d;}
public void moveDown(int d) {y = y + d;}
public void gogo() {yes = true;}
public void nono() {yes = false;}

public static void main(String[] args) {
    JFrame frame = new Viewer();
    frame.setSize(500, 500);
    frame.setTitle("Bouncing Ball");
    frame.setDefaultCloseOperation((JFrame.EXIT_ON_CLOSE));
    frame.setVisible(true);
}
}

Viewer Class:

public class Viewer extends JFrame {
JButton go = new JButton("GO");
JButton stop = new JButton("STOP");
JPanel buttons = new JPanel();
Timer timer;

ControlledBall cbPanel = new ControlledBall();
JPanel left = new JPanel();
JPanel right = new JPanel();
JPanel top = new JPanel();


class gogoListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        cbPanel.gogo();
        timer.start();
    }
}

class nonoListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        cbPanel.nono();
        timer.stop();
    }
}

class TimerListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        cbPanel.moveRight(5);
        cbPanel.moveDown(5);
        repaint();
    }
}

public Viewer() {
    buttons.add(go);
    buttons.add(stop);
    this.add(buttons, BorderLayout.SOUTH);
    this.add(cbPanel, BorderLayout.CENTER);
    this.add(right, BorderLayout.EAST);
    this.add(top, BorderLayout.NORTH);
    this.add(left, BorderLayout.WEST);

    timer = new Timer(50, new TimerListener());
    go.addActionListener(new gogoListener());
    stop.addActionListener(new nonoListener());
    timer.start();
    cbPanel.setBorder(BorderFactory.createLineBorder(Color.black));
}

}

See [Collision detection with complex shapes](http://stackoverflow.com/q/14574045/418556) for a working example. Though admittedly a circle (the ball) and the displayable area (a rectangle) would leave it open to a much simpler formula than the JRE performs in my example. — Andrew Thompson, Apr 22 '14 at 04:47

score 2 · Answer 1 · edited May 23 '17 at 12:11

You need some kind of delta which determines the direction that the ball is moving in, instead of calling moveRight/moveDown, you would simply ask the ball to update itself based on this delta.

When (the update method is) called, it will apply the current delta to the x/y position and evaluate if the ball has passed beyond the available bounds, if it has the ball should repositioned on the edge and the delta flipped (multiplied by -1), which will change the direction of the delta.

You will need a delta for both the horizontal and vertical positions ;)

For example:

Java: Ball Collision with Frame

1 Answers1