1 /* 2  * 程序可以用鼠标拖拽话出一个矩形； 3  */ 4 import acm.graphics.*; 5 import acm.program.*; 6 import java.awt.event.*; 7  8 public class DrawRectangle extends GraphicsProgram{ 9     //鼠标侦听10     public void run(){11         addMouseListeners();12     }13     //鼠标按下事件14     public void mousePressed(MouseEvent e){15         press = new GPoint(e.getPoint());16         rect = new GRect(0,0);17     }18     //鼠标拖拽事件19     public void mouseDragged(MouseEvent e){20         double x = press.getX();21         double y = press.getY();22         double width = e.getX() - press.getX();23         double height = e.getY() - press.getY();24         //确保向左下方拖拽也能画出矩形；25         if(width < 0 ){26             x = e.getX();27             width = -width;28         }29         //确保向上方拖拽也能画出矩形；30         if(height < 0){31             y = e.getY();32             height = -height;33         }34         35         rect.setSize(width,height);36         rect.setFilled(true);37         add(rect, x, y);38     }39     private GPoint press; //记录鼠标按下的点；40     private GRect rect;41 }

设置 一个 Grect 实例变量，使用 setSize方法改变矩形大小