Java creating multiple Balls using paintcomponent

Question

I want to create a method that creates 5 balls on a panel. Can somebody please help me get around this using the paint component method or creating my own draw method. As you can see bellow, i have a paint component method with a for loop that will loop 5 and create a ball in a random location, but unfortunately only one ball is being created.

import java.awt.*;
import java.util.Random;
import javax.swing.*;

public class AllBalls extends JPanel {
    int Number_Ball=5;
    int x,y;
    Graphics g;
    AllBalls(){
        Random r = new Random();
        x=r.nextInt(320);
        y=r.nextInt(550);
    }
public static JFrame frame;
    public static void main(String[] args) {
        AllBalls a= new AllBalls();
        frame= new JFrame("Bouncing Balls");
        frame.setSize(400,600);
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.add(a);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        for(int i=0;i<Number_Ball;i++){
            g.fillOval(x, y, 30, 30);
        }
        repaint();
    }

}

try `g.fillOval(i*30, 0, 30, 30);`, I think you are drawing them all at the same location. — JackWhiteIII, Jul 11 '15 at 15:24
Thanks that did it.. but they are not in a random location, as you can see i set my x and y to be a random number. — user3500147, Jul 11 '15 at 15:32

score 4 · Accepted Answer · answered Jul 11 '15 at 15:36

    Random r = new Random();
    x=r.nextInt(320);
    y=r.nextInt(550);

You only create one random point, not 5.

If you want 5 random points then you need to create an ArrayList to store your 5 random points. Something like:

ArrayList<Point> balls = new ArrayList<Point>(5); // instance variable

AllBalls()
{
    Random r = new Random();

    for (int i = 0; i < 5; i++)
        balls.add( new Point(r.nextInt(320), r.nextInt(550));
}

Then in the paintComponent() method you need to iterate through all the points:

for (Point p: balls)
    g.fillOval(p.x, p.y, 30, 30);

Also, get rid of the repaint() statement. Never invoke repaint() in a painting method, this will cause an infinite loop.

Java creating multiple Balls using paintcomponent

1 Answers1