Board

import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import javax.swing.JPanel;

public class Board extends JPanel implements Runnable, KeyListener {

    Balls balls = new Balls();
    private Boolean shoot = false;

    // ////////////////////////////////////////////////////CONSTRUCTOR
    public Board() {
        setFocusable(true);
        Thread t = new Thread(this);
        addKeyListener(this);
        t.start();
    }

    // ///////////////////////////////////////////////////PAINT
    public void paint(Graphics g) {
        super.paint(g);
        if (shoot) {
            balls.draw(g);
        }
    }

    // //////////////////////////////////////////////////KEY LSITENER
    public void keyPressed(KeyEvent e) {
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_SPACE) {
            shoot = true;
        }
    }

    public void keyReleased(KeyEvent e) {}
    public void keyTyped(KeyEvent e) {}

    // ///////////////////////////////////////////////////UPDATER
    public void update() {

        if (shoot) {
            balls.move(this.getHeight(), this.getWidth());
        }
    }

    // //////////////////////////////////////////////////MAIN THREAD
    @Override
    public void run() {
        while (true) {
            update();
            repaint();
            try {
                Thread.sleep(17);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    }
}