Moving Image randomly multiple times

I found a nice answer about moving images multiple times here:

http://ift.tt/2qhHXL2

It's really helpful for what i want to achieve in my program but I need one more thing. Fireballs are stored in List and they are painted when we press SPACE. I want to generate them randomly. Is there any simple way to do that?

Code from topic:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import java.util.*;
import java.util.List;
import java.util.logging.*;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.Timer;

public class WannaBeStreetFighter extends JPanel {

private static final int D_W = 700;
private static final int D_H = 250;
private static final int X_INC = 10;

List<Fireball> fireBalls;
BufferedImage ryu;
BufferedImage fireball;
BufferedImage background;

public WannaBeStreetFighter() {

    try {
        ryu = ImageIO.read(new URL("http://ift.tt/2pu4n8X"));
        background = ImageIO.read(new URL("http://ift.tt/2qi3xPr"));
        fireball = ImageIO.read(new URL("http://ift.tt/2pujXkM"));
    } catch (IOException ex) {
        Logger.getLogger(WannaBeStreetFighter.class.getName()).log(Level.SEVERE, null, ex);
    }

    fireBalls = new LinkedList<>();

    Timer timer = new Timer(40, new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            Iterator<Fireball> it = fireBalls.iterator();
            while (it.hasNext()) {
                Fireball ball = it.next();
                if (ball.x > D_W) {
                    it.remove();
                    System.out.println(fireBalls.size());
                } else {
                    ball.x += X_INC;
                    repaint();
                }
            }
        }
    });
    timer.start();

    InputMap inputMap = getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
    inputMap.put(KeyStroke.getKeyStroke("SPACE"), "hadouken");
    getActionMap().put("hadouken", new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            fireBalls.add(new Fireball(fireball));
        }
    });

}

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawImage(background, 0, 0, D_W, D_H, this);
    g.drawImage(ryu, 50, 125, 150, 115, this);
    for (Fireball ball : fireBalls) {
        ball.drawFireball(g);
    }
}

@Override
public Dimension getPreferredSize() {
    return new Dimension(D_W, D_H);
}

private class Fireball {

    Image fireball;
    int x = 150;
    int y = 125;

    public Fireball(Image image) {
        fireball = image;
    }

    public void drawFireball(Graphics g) {
        g.drawImage(fireball, x, y, 75, 50, null);
    }
}

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            JFrame frame = new JFrame("Best Street Fighter ever");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(new WannaBeStreetFighter());
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        }
    });
}
}