java 画线问题

import java.awt.*;
import java.awt.event.*;
public class Ex13_2 extends Frame implements Runnable
{
int currentX=0,currentY=0;
int startX=0,startY=0;
public static void main(String []args)
{
Ex13_2 workstart=new Ex13_2();
}
public Ex13_2()
{
super("Ex13_2");
setSize(350,350);

enableEvents(AWTEvent.MOUSE_EVENT_MASK);
enableEvents(AWTEvent.WINDOW_EVENT_MASK);

setVisible(true);
new Thread(this).start();
}

public void processWindowEvent(WindowEvent e)
{
if(e.getID()==WindowEvent.WINDOW_CLOSING)
{
System.exit(0);
}
}

public void processMouseEvent(MouseEvent e)
{
if(e.getID()==MouseEvent.MOUSE_PRESSED)
{
startX=e.getX();
startY=e.getY();
}
if(e.getID()==MouseEvent.MOUSE_MOVED||e.getID()==MouseEvent.MOUSE_DRAGGED)
{
currentX=e.getX();
currentY=e.getY();
//repaint();
}

}
public void run()
{
while(true)
{
repaint();
try{Thread.sleep(30);}
catch(InterruptedException e){;}
}
}
public void paint(Graphics g)
{
g.drawLine(startX,startY,currentX,currentY);
}

}

怎么改？

鼠标画线程序，我给你改了两处（见注释），现在运行没问题了，你看看吧。
import java.awt.*;
import java.awt.event.*;
public class Ex13_2 extends Frame implements Runnable
{
int currentX=0,currentY=0;
int startX=0,startY=0;
public static void main(String []args)
{
Ex13_2 workstart=new Ex13_2();
}
public Ex13_2()
{
super("Ex13_2");
setSize(350,350);

enableEvents(AWTEvent.MOUSE_EVENT_MASK );
enableEvents(AWTEvent.MOUSE_MOTION_EVENT_MASK); //这里加了一句
enableEvents(AWTEvent.WINDOW_EVENT_MASK);

setVisible(true);
new Thread(this).start();
}

public void processWindowEvent(WindowEvent e)
{
if(e.getID()==WindowEvent.WINDOW_CLOSING)
{
System.exit(0);
}
}
public void processMouseMotionEvent(MouseEvent e){ //这里加了一个函数并且把processMouseEvent函数中的鼠标移动判断移到这里
if(e.getID()==MouseEvent.MOUSE_MOVED || e.getID()==MouseEvent.MOUSE_DRAGGED)
{
currentX=e.getX();
currentY=e.getY();
}
}

public void processMouseEvent(MouseEvent e)
{
if(e.getID()==MouseEvent.MOUSE_PRESSED)
{
startX=e.getX();
startY=e.getY();
}
}
public void run()
{
while(true)
{
repaint();
try{Thread.sleep(30);}
catch(InterruptedException e){;}
}
}
public void paint(Graphics g)
{
g.drawLine(startX,startY,currentX,currentY);
}
}