我用的是J++,我想实现---当鼠标进入小应用程序的窗口范围时屏幕显示"鼠标已进入..",当鼠标退出小应用程序的窗口范围时屏幕显示"鼠标已退出..",但是没反应
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Event;

public class Demo28 extends java.applet.Applet
{
String CurrentMessage="";

public boolean mouseEnter(Event evt,int x,int y)
{
CurrentMessage="鼠标已进入......";
repaint();
return true;
}

public boolean mouseExit(Event evt,int x,int y)
{
CurrentMessage="鼠标已退出......";
repaint();
return true;
}

public void paint(Graphics g)
{
g.drawString(CurrentMessage,5,15);
}
}

import java.awt.event.*;
...
addMouseListener(new MouseAdapter(){
public boolean mouseEnter(MouseEvent evt)
    {
            CurrentMessage="鼠标已进入......";
            repaint();
            return true;
    }
    
    public boolean mouseExit(MouseEvent)
    {
            CurrentMessage="鼠标已退出......";
            repaint();
            return true;
    }
    
    

});

import java.awt.Graphics;
import java.awt.Point;
import java.awt.Event;

public class Demo28 extends java.applet.Applet
{
String CurrentMessage="";

public boolean mouseMove(Event evt,int x,int y)
{
CurrentMessage="鼠标已进入......";
repaint();
return true;
}

public boolean mouseExit(Event evt,int x,int y)
{
CurrentMessage="鼠标已退出......";
repaint();
return true;
}

public void paint(Graphics g)
{
g.drawString(CurrentMessage,5,15);
}
}

init()
{
    //击活鼠标事件
    enableEvents(MouseEvent.MOUSE_MOVED);
}
/**处理鼠标移动事件,源于:enableEvent(MouseEvent.MOUSE_RELEASED)**/
protected void processMouseEvent(MouseEvent me){
}
/**处理鼠标移动事件,源于:enableEvent(MouseEvent.MOUSE_MOVED)**/
protected void processMouseMotionEvent(MouseEvent me){
}

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.Robot.*;


public class TestMouse extends Applet implements MouseListener,MouseMotionListener
{
   public void init()
   {
       this.addMouseListener(this);
       this.addMouseMotionListener(this);
   }

   public void mouseClicked(MouseEvent e)
   {
       if(e.getClickCount()==1)
          showStatus("You single hit at X--"+e.getX()+"--Y--"+e.getY());
       else
          if(e.getClickCount()==2)
             showStatus("You double hit at X--"+e.getX()+"--Y--"+e.getY());

        try{Robot m_Robot=new Robot();
          m_Robot.mouseMove(500,500);
        }
        catch(Exception ee){}

   }

   public void mouseEntered(MouseEvent e)
   {
      showStatus("mouse into applet");
      Integer.valueOf("222").intValue();
       // Point pp=null;
       // pp.x=50;
       // pp.y=50;
       // e.translatePoint(50,350);
   }

   public void mouseExited(MouseEvent e)
   {
      showStatus("mouse leave applet");
   }

   public void mousePressed(MouseEvent e)
   {
     showStatus("down mouse");
   }
    public void mouseReleased(MouseEvent e)
   {
     showStatus("up mouse");
   }

    public void mouseMoved(MouseEvent e)
   {
     //showStatus("X: "+e.getX()+"Y: "+e.getY());

   }

    public void mouseDragged(MouseEvent e)
   {
     showStatus("Dragged mouse");
   }
}

import java.awt.event.*;
...
addMouseListener(new MouseAdapter(){
public boolean mouseEntered(MouseEvent evt)
    {
            CurrentMessage="鼠标已进入......";
            repaint();
            return true;
    }
    
    public boolean mouseExited(MouseEvent)
    {
            CurrentMessage="鼠标已退出......";
            repaint();
            return true;
    }
 

在java中处理事件要注册监听器。