Java中的repaint（）方法无法正常工作

Question

am doing that program to paint the mouse location in a panel , the program works fine but after like 10 seconds it stops painting the points... any help?

   import java.awt.Color;
   import java.awt.Graphics;
   import javax.swing.JPanel;
   import javax.swing.JFrame;
    public class Draw extends JPanel {
public static  int newx;
public static  int newy;

   public void paint(Graphics g) {    

  Mouse mouse = new Mouse();
  mouse.start();

int newx = mouse.x;
int newy = mouse.y;
 g.setColor(Color.blue);  
   g.drawLine(newx, newy, newx, newy);
   repaint();




   }

   public static void main(String[] args) {

  JFrame frame = new JFrame("");
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setBackground(Color.white);
  frame.setSize(2000,2000 );
  frame.setVisible(true);
  frame.getContentPane().add(new Draw());
  frame.revalidate();
  frame.getContentPane().repaint();


  }
 }

Answer 1

You call repaint within the paint method, causing an infinite loop. Swing Timers are preferred for running periodic updates on components.

For custom painting in Swing the method paintComponent rather than paint should be overridden not forgetting to call super.paintComponent .

Answer 2

public void paint(Graphics g) should be public void paintComponent(Graphics g) .

And you isn't supposed to call repaint() inside this method.

You should add an mouse listener outside this method, too.

An adapted example from Java Tutorials

public class MouseMotionEventDemo extends JPanel 
                                  implements MouseMotionListener {
    //...in initialization code:
        //Register for mouse events on blankArea and panel.
        blankArea.addMouseMotionListener(this);
        addMouseMotionListener(this);
        ...
    }

    public void mouseMoved(MouseEvent e) {
       Point point = e.getPoint();
       updatePanel(point); //create this method to call repaint() on JPanel.
    }

    public void mouseDragged(MouseEvent e) {
    }


    }
}