Java graphics isn't repainting

问题:

I want to add in a feature so that when the mouse goes over a button then it will add a drop shadow. Currently I'm just trying to get the mechanics to work. I have my game loop calling a update method which I know works but here it is anyway

    public void updateManager(double delta){
    mhandler.updateCoordinates();
    if(mhandler.getX() >= 144 && mhandler.getX() <= 444 && mhandler.getY() >= 784 && mhandler.getY() <= 980){
        oversp = true;
    }else{
        oversp = false;
    }
}

mhandler is what I named my MouseHandler class. then i have my render method

    public void render(){
    repaint();
}

and then my paint method

    public void paintComponent(Graphics g) {
    Graphics2D g2d = (Graphics2D) g;

    if(oversp){
        System.out.println("Is over button");
        g2d.setColor(Color.RED);
        g2d.fillRect(144, 784, 300, 169);
    }else{
        System.out.println("Not over button");
        g2d.setColor(Color.BLACK);
        g2d.fillRect(144, 784, 300, 169);
    }
}

When ever i run the program it only prints out not over button twice even when i am constantly calling render() in my game loop. I really do not know why it is not repainting. any help is very appriciated!

This is how I detect my coordinates of mouse

    private int x,y;

public MouseHandler(){
    x = 0;
    y = 0;
}

public void updateCoordinates(){
    PointerInfo a = MouseInfo.getPointerInfo();
    Point b = a.getLocation();
    x = (int) b.getX();
    y = (int) b.getY();
}

public int getX(){
    return x;
}

public int getY(){
    return y;
}

Game loop code

    public static void MenuLoop() {
    long lastLoopTime = System.nanoTime();
    final int TARGET_FPS = 60;
    final long OPTIMAL_TIME = 1000000000 / TARGET_FPS;
    long lastFpsTime = 0;
    int fps = 0;
    while (isrunning) {
        long now = System.nanoTime();
        long updateLength = now - lastLoopTime;
        lastLoopTime = now;
        double delta = updateLength / ((double) OPTIMAL_TIME);

        lastFpsTime += updateLength;
        fps++;

        if (lastFpsTime >= 1000000000) {
            System.out.println("(FPS: " + fps + ")");
            lastFpsTime = 0;
            fps = 0;
        }

        menu.render();
        menu.updateManager(delta);


        try {
            Thread.sleep((lastLoopTime - System.nanoTime() + OPTIMAL_TIME) / 1000000);
        } catch (Exception e) {

        }
    }

}public static void MenuLoop() {
    long lastLoopTime = System.nanoTime();
    final int TARGET_FPS = 60;
    final long OPTIMAL_TIME = 1000000000 / TARGET_FPS;
    long lastFpsTime = 0;
    int fps = 0;
    while (isrunning) {
        long now = System.nanoTime();
        long updateLength = now - lastLoopTime;
        lastLoopTime = now;
        double delta = updateLength / ((double) OPTIMAL_TIME);

        lastFpsTime += updateLength;
        fps++;

        if (lastFpsTime >= 1000000000) {
            System.out.println("(FPS: " + fps + ")");
            lastFpsTime = 0;
            fps = 0;
        }

        menu.render();
        menu.updateManager(delta);


        try {
            Thread.sleep((lastLoopTime - System.nanoTime() + OPTIMAL_TIME) / 1000000);
        } catch (Exception e) {

        }
    }

}

回答1:

The Event Dispatch Thread contains a queue to which all AWT events are added. Whenever you call repaint, a paint event will be queued on the Event Dispatch Thread.

So if you're in an infinite loop while on the Event Dispatch Thread, those paint events will stand in line forever, waiting for the infinite loop to end. That's why paintComponent is never called.

The solution would be to replace the infinite loop with a Swing timer.

Timer timer = new Timer(1000 / TARGET_FPS, new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        //...
    }
});
timer.start();