看看这个程序，40分

Question

what is the problem?
当然是画的框不对！高手快来！

Answer 1

在init()方法里加上
addMouseListener(this);

Answer 2

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.image.*;
public class TMouseMotion extends JApplet implements MouseListener
{
    int x,y;
    int o_x,o_y;
    int flag;
      int s_x;
    int s_y;
    int width;
    int height;
    public void init()
    {
        CustomListener ct=new CustomListener(this);
        this.addMouseMotionListener(ct);
        addMouseListener(this);//You missed this line
    }
    public void update(Graphics g)
    {
        paint(g);
    }
    public void paint(Graphics gdraw)
    {
BufferedImage bufimg=new BufferedImage(getWidth(),getHeight(),BufferedImage.TYPE_INT_ARGB);
Graphics g=bufimg.getGraphics();
        g.setColor(this.getBackground());
        g.fillRect(0,0,getWidth(),getHeight());
       g.setColor(Color.blue);
        g.drawString("drag/move mouse......",5,20);
        g.setColor(Color.red);
        if(flag==1)
        {
            g.drawString("don't move!drag the mouse",5,85);
            g.drawString("cursor coordinates:"+x+","+y,5,95);
        }
        else if(flag==2)
        {
            g.drawString("don't drag!move the mouse",5,85);
            g.drawString("cursor coordinates:"+x+","+y,5,95);
        }
        g.setColor(Color.blue);
        g.drawRect(s_x,s_y,width,height);
        gdraw.drawImage(bufimg,0,0,null);
    }    public void mousePressed(MouseEvent e)
    {
        o_x=e.getX();
        o_y=e.getY();
    }
    public void mouseReleased(MouseEvent e)
    {
        o_x=0;
        o_y=0;
    }
    public void mouseClicked(MouseEvent e)
    {
    }
    public void mouseEntered(MouseEvent e)
    {
    }
    public void mouseExited(MouseEvent e)
    {
    }
}
class CustomListener implements MouseMotionListener
{
    TMouseMotion tm;
    public CustomListener(TMouseMotion tm)
    {
        this.tm=tm;
    }
    public void mouseMoved(MouseEvent e)
    {
        tm.flag=2;
        tm.x=e.getX();
        tm.y=e.getY();
        tm.repaint();
    }
    public void mouseDragged(MouseEvent e)
    {
        tm.flag=1;
        tm.x=e.getX();
        tm.y=e.getY();
        if(tm.x>=tm.o_x && tm.y<=tm.o_y)
        {
            tm.s_x=tm.o_x;
            tm.s_y=tm.y;
            tm.width=tm.x-tm.o_x;
            tm.height=tm.o_y-tm.y;
        }
        if(tm.x>=tm.o_x && tm.y>=tm.o_y)
        {
            tm.s_x=tm.o_x;
            tm.s_y=tm.o_y;
            tm.width=tm.x-tm.o_x;
            tm.height=tm.y-tm.o_y;
        }
        if(tm.x<=tm.o_x && tm.y>=tm.o_y)
        {
            tm.s_x=tm.x;
            tm.s_y=tm.o_y;
            tm.width=tm.o_x-tm.x;
            tm.height=tm.y-tm.o_y;
        }
        if(tm.x<=tm.o_x && tm.y<=tm.o_y)
        {
            tm.s_x=tm.x;
            tm.s_y=tm.y;
            tm.width=tm.o_x-tm.x;
            tm.height=tm.o_y-tm.y;
        }        tm.repaint();    }}

Answer 3

在init中少了 
addMouseListener(this);