定时器和 JFrame 出错

问题描述

I'm making a game with a timer and a JFrame (and many other things but only these 2 are causing problems), and after running the segments below, I got a weird error. At least for me who has never used these classes prior to this.

Start executing this

private static GameView window;
private static Timer time;
public static void main(String args[])
{
    window = new GameView(800,600);
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setVisible(true);

    time = new Timer();
    time.schedule( new TimerTask(){
        public void run(){GameState.update(); 
        window.paintComponents(null);}
        },0, 40);

}

which calls this:

public void paintComponents (Graphics g)
{

    for(Bullet j : GameState.getEnBullets()){
        g.drawImage(j.getImage(),j.getX(), j.getY(), null);}
    for(Enemy j : GameState.getEnemies()){
        g.drawImage(j.getImage(),j.getX(), j.getY(), null);}
    for(Bullet j : GameState.getPlayBullets()){
        g.drawImage(j.getImage(),j.getX(), j.getY(), null);}
    this.paint(g);
}

And here's the error:

Exception in thread "Timer-0" java.lang.NullPointerException
    at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
    at java.awt.Container.paint(Unknown Source)
    at java.awt.Window.paint(Unknown Source)
    at Game.GameView.paintComponents(GameView.java:59)
    at Game.GameController$1.run(GameController.java:39)
    at java.util.TimerThread.mainLoop(Unknown Source)
    at java.util.TimerThread.run(Unknown Source)

I also get a blank JFrame window (GameView extends JFrame).

The method to override is paintComponent() not "paintComponents" (with an s).

You should never invoke the paintComponent() method directly. Instead you invoke the repaint() method on the component.

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