拖动鼠标画虚线矩形

import java.awt.geom.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
/**
*简单的画图程序
*@author Eastsun
*@version .1
*/
public class DrawPanel extends JFrame{
   LinkedList<Shape> shapeList =new LinkedList<Shape>();
   Shape shape;
   Point start,end;
   final String[] type =new String[]{"Line","Rectangle","Ellipse"};
   JComboBox comboBox =new JComboBox(type);
   public DrawPanel(){
      super("DrawPanel");
      JPanel panel =new JPanel(){
        public void paintComponent(Graphics g){
           super.paintComponent(g);
           Graphics2D g2 =(Graphics2D)g;
           g2.setColor(Color.white);
           g2.fillRect(0,0,getWidth(),getHeight());
           g2.setColor(Color.black);
           for(Shape s:shapeList) g2.draw(s);
           g2.draw(shape);
        }
      };
      panel.addMouseListener(new MouseAdapter(){
        public void mousePressed(MouseEvent e){
           start =e.getPoint();
        }
        public void mouseReleased(MouseEvent e){
           shapeList.add(shape);
        }
      });
      panel.addMouseMotionListener(new MouseMotionAdapter(){
        public void mouseDragged(MouseEvent e){
           end =e.getPoint();
           Object select =comboBox.getSelectedItem();
           if(select.equals(type[0])) shape =new Line2D.Float(start,end);
           else{
              if(select.equals(type[1]))  shape =new Rectangle();
              else                shape =new Ellipse2D.Float();
              ((RectangularShape)shape).setFrameFromDiagonal(start,end);
           }
           repaint();
        }
      });
      panel.setPreferredSize(new Dimension(320,240));
      add(panel,BorderLayout.NORTH);
      shape =new Rectangle();
      
      add(comboBox,BorderLayout.SOUTH);
      
      pack();
      setResizable(false);
      setDefaultCloseOperation(EXIT_ON_CLOSE);
      setVisible(true);
      
   }
   public static void main(String[] args){
      new DrawPanel();
   }
}