在swing中怎样才能把鼠标的活动范围限制在某个窗体内

package com.ddpie;

import java.awt.awtexception;
import java.awt.graphicsdevice;
import java.awt.graphicsenvironment;
import java.awt.robot;
import java.awt.event.mouseevent;
import java.awt.event.mousemotionlistener;

import javax.swing.jframe;

public class testcursorframe {

    public static void main（string[] args) throws awtexception{
        final int width = 300;
        final int hight = 200;
        
        final jframe frame = new jframe（);
        frame.setsize（width, hight);
        frame.setlocation（200, 200);
        frame.setundecorated（true);
        frame.setdefaultcloseoperation（jframe.exit_on_close);
        frame.setvisible（true);
        
        graphicsenvironment env = graphicsenvironment.getlocalgraphicsenvironment（);
        graphicsdevice screen = env.getdefaultscreendevice（);
        final robot robot = new robot（screen);
        
        frame.addmousemotionlistener（new mousemotionlistener（){
            public void mousedragged（mouseevent e) {
                resetcursorpos（e);
            }
            public void mousemoved（mouseevent e) {
                resetcursorpos（e);
            }
            private void resetcursorpos（mouseevent e){
                int curx = e.getx（)+frame.getx（);
                int cury = e.gety（)+frame.gety（);
                
                int frameleft = frame.getx（)+20;
                int frameright = frame.getx（)+frame.getwidth（)-20;
                int frameup = frame.gety（)+20;
                int framedown = frame.gety（)+frame.getheight（)-20;
                
                int x = curx;
                int y = cury;
                
                if（curx<frameleft){
                    x = frameleft;
                }
                if（curx>frameright){
                    x = frameright;
                }
                if（cury<frameup){
                    y = frameup;
                }
                if（cury>framedown){
                    y = framedown;
                }
                if（x!=curx || y!=cury)
                    robot.mousemove（x, y);
            }
        });
    }
}