恰好以前给别人写过一个示例：

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 [url=http://eastsun.javaeye.com]Eastsun[/url]
*@version .1
*/
public class DrawPanel extends JFrame{
  LinkedList<Shape> shapeList =new LinkedList<Shape>();
  Shape shape;
  Stroke stroke =new BasicStroke(1.0f,BasicStroke.CAP_ROUND,BasicStroke.JOIN_ROUND,
                                      0,new float[]{8f,3f},1);
  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);
          if(shape!=null){
            g2.setStroke(stroke);
            g2.setPaint(Color.blue);
            g2.draw(shape);
          }
        }
    };
    panel.addMouseListener(new MouseAdapter(){
        public void mousePressed(MouseEvent e){
          start =e.getPoint();
        }
        public void mouseReleased(MouseEvent e){
          if(shape!=null) shapeList.add(shape);
          shape =null;
          repaint();
        }
    });
    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);
    
    add(comboBox,BorderLayout.SOUTH);
    
    pack();
    setResizable(false);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
    
  }
  public static void main(String[] args){
    new DrawPanel();
  }
}

[此贴子已经被作者于2007-3-1 21:53:23编辑过]