对象不会出现在Java swing的按键上

Question

So I am trying to make a very simple game in Java using swing. It's a space invaders type game and I have successfully coded in the spaceship that moves left and right with key presses. However I am having a lot of trouble getting the "shot" to show up.

I am not looking to position it just yet, I really just want to create an object on keypress to make it work. I am assuming since it is not initially in the "paint" method, that is why it is not appearing. But I don't know how to make it show up! Any ideas?

For reference here is current code:

public void keyPressed(KeyEvent e) {
    if (KeyEvent.VK_RIGHT == e.getKeyCode()) {
        moveRight();
    }
    if (KeyEvent.VK_LEFT == e.getKeyCode()) {

        moveLeft();
    }
    if (KeyEvent.VK_SPACE == e.getKeyCode()) {
        shoot();

    }
}

public void shoot() {
    Laser laser = new Laser(new Point(200, 200));
    this.repaint();
}

public void moveLeft() {
    if (player.getCentre().getX() <= 20) {
        player.setX(20);
    } else {
        double movement = player.getCentre().getX();
        movement -= 10;
        player.setX(movement);
    }
    this.repaint();
}

@Override
public void paint(Graphics g) {
    setBackground(Color.black);
    super.paint(g);
    player.draw(g);

}

I just want to make shoot() successfully create an object and have it show up in my panel!

Answer 1

Problems/Suggestions:

• Your shoot method creates an object just fine, but then completely ignores it. You don't add your newly created Laser object to anything, not to a field of the class, not to any ArrayList, and not to any other collection, so the class will have no knowledge that the object exists, and once the method where it was created ends, the object is primed for garbage collection since it only exists locally within the method.
• We have no idea if your KeyListener is working or not. Have you debugged this part with println statements? If not I'd do this.
• I'd avoid KeyListeners in general in favor of Key Bindings as the latter is much less fidgety regarding focus requirements
• As a general rule, don't override JPanel's paint method but rather its paintComponent method, and be sure to call the super's method within your override.
• Your GUI will only paint what you tell it to paint, and currently your painting method is only asking to have the Player's state painted but nothing else. If you want a laser blast painted, then the painting method, which again should be a protected void paintComponent(Graphics g) override and not a public void paint(Graphics g) override, should contain code to do this.

We're a bit limited in any advice that we can give since you've posted a code snippet, one that we can't compile or run. If these suggestions don't lead you to an answer, then please create and post a small but simple complete program that illustrates your problem, an MCVE . Please check the link for the details of this very useful tool.