Move object with mouse cursor - Java

Question

I have to do the Agario game using object oriented programming with Java. So far I've draw a circle and I was able to make it follow my cursor. However I have many bugs like the ball not following the cursor after the cursor touches the ball, sometimes, the ball moves to quickly, other times it moves to slowly.

Overall I think it's far from perfect and would like some suggestions. I just have to make it follow and I'm struggling a bit. Here's the code:

window class:

public class window extends JFrame implements Runnable {

  Ball b = new Ball();
  Thread t = new Thread(this);

  public window () {
    setSize(600, 600);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setResizable(true);
    setLocationRelativeTo(null);
    setVisible(true);
    t.start();

    addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
        public void mouseMoved(java.awt.event.MouseEvent evt) {
            formMouseMoved(evt);
        }

    });

  }

  private void formMouseMoved(MouseEvent evt) {
    b.setnewtarget(evt.getX(), evt.getY());
  }

  @Override
  public void paint(Graphics g) {
    super.paint(g); //To change body of generated methods, choose Tools | Templates.
    b.drawCenteredCircle(g);
  }

  public static void main(String[] args) {
    new window ();
  }

  @Override
  public void run() {
    while (true) {
        repaint();
    }
  }

}

Here´s the Ball class:

public class Ball implements Runnable {

  Thread t = new Thread(this);
  int x, y, r;
  int targetx, targety;

  public Ball() {
    x = 300;
    y = 300;
    r = 35;
    t.start();
  }

  public void drawCenteredCircle(Graphics g) {
    g.fillOval(x, y, r, r);
    g.drawLine(x, y, targetx, targety);
  }

  @Override
  public void run() {
    while (true) 

         int dx = Math.abs(targetx-x);
         int dy = Math.abs(targety-x);

         if (dx > dy) {
            int oldx = x;
            if (x > targetx)
               x--;
            else
               x++;

            y =((targety-y)/(targetx-x))*(x-oldx)+y;
         } else {
            int oldy = y;
            if (y > targety)
               y--;
            else
               y++;

            x =((targetx-x)/(targety-y))*(y-oldy)+x;
         }

        try {
            t.sleep(10);
        } catch (InterruptedException ex) {
            Logger.getLogger(Bola.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
  }

  void setnewtarget(int x, int y) {
    targetx = x;
    targety = y;
  }
}

Thanks :D

Answer 1

1. There is no need for the Thread. You should NOT be using the infinite while loop. Get rid of that code

2. In the formMouseMoved(...) moved method you invoked repaint() which will cause the component to paint itself.

3. Also, get rid of the Thread and while loop in your Ball class.

The key point is that Swing is event driven. The mouseMoved(...) event is all you need for the animation. Every time you drag the mouse an event will be generated which will cause you to repaint the Ball.