[说明]
以下程序实现了利用鼠标任意移动圆形的位置，仔细阅读代码和相关注释，将程序补充完整。
[代码6-1]
import java.awt.*;
import java.awt.event.*;
public class CIUSAMPLE extends Frame implements MouseMotionListener, MouseListener
static CIUSAMPLE frm=new CIUSAMPLE ( );
int x=70,y=60,posX=70,posY=60,dx,dy;
public static void main (String args[])
frm.setTitle ("Dragging a circle");
frm.setSize (200,150);
(1)
ffm.addMouseMotionListener (frm);
frm.setVisible (true);
public void mousePressed (MouseEvent e)
(2)
dy=e.getY ( ) -posY;
public void mouseDragged (MouseEvent e)
(3)
y=e.getY ( ) -dy;
if(dx＞0&&dx＜50&&dy＞0&&dy＜50) //如果指针落在正方形区域内
Graphicsg=getGraphics ( );
(4)
public void paint (Graphics g)
g.setColor (Color.pink); //设置绘图颜色为粉红
g.fillOval(x,y,50,50); //以基准点为图形在左上角绘出圆形
(5)
posY=y；
public void mouseMoved (MouseEvent e)
public void mouseReleased (MouseEvent e)
public void mouseEntered (MouseEvent e)
public void mouseExited (MouseEvent e)
public void mouseClicked (MouseEvent e)
参考答案：(1)frm.addMouseListener (frm);
(2)dx=e.getX()-posX;
(3)x=e.getX()-dx;
(4)update(g);
(5)posX=x;
解析： 以下程序实现了利用鼠标任意移动该圆形的位置。分析代码可知(1)实现了对鼠标位置的检测；(2)取得鼠标按下之点与基准点X方向的距离；(3)取得拖曳时的基准点X价码标；(4)清空画面为背景颜色；(5)更新基准点的X坐标。