How to prevent latency while using too much repaint

Question

I am trying to make a little game, a plane is up and when i click the down arrow it drops a bomb. If bomb hit the target it changes its place etc...

public void paint(Graphics p) {
    p.setColor(c);
    p.drawLine(0, 650, 1000, 650);

    p.fillRect(x3, y3, 150, 50);
    p.fillOval(x2, y2, 30, 30);
    p.drawImage(image, x, y, null);

    if (x < 1000) {
        x = x + 10;
    }

    if (x > 750) {
        x = 0;
    }

    try {
        Thread.sleep(40);
    } catch (InterruptedException ignored) {
    }

    if (bo==true) {
        x2 = x2 + z;
        y2 = y2 + 8;
    }

    if (y2 > 450 && z != 0) {
        z--;
    }

    if (y2 > 620) {
        x2 =- 100;
        y2 =- 100;
    }

    if (y2 > 610 && x2 < x3 + 150 && x2 > x3) {
        x3 = x3 + 100;
    }

    repaint(1);
}

But the problem is at first everything is normal after 1 or 2 seconds fps is like 10, sometimes i cant see the objects, i saw another topic about using timer but i dont want to solve it with timer and even i dont know if i could. I wonder if its about my computer or ide.

Answer 1

First of all, do not Override paint() method. Override paintComponent(Graphics g) method (and do not forget to call super.paintComponent(g).

Secondly, using Thread.sleep() method in EDT (hopefully, you start your application, using SwingUtilities#invokeLater) is bad idea, since all events will stop taking place (with few words, the whole GUI will freeze).

You should use a swing Timer instead.

Finally, do not call repaint() inside paintComponent, because repaint() will call paintComponent again, and it will be an endless loop. You should repaint the component in Timer`s action listener.