example18_2.java.bak

不错的教程 适合中高级人员的使用

import java.awt.*;import java.awt.event.*;
class MyCanvas extends Canvas implements MouseListener
{  int left=-1,right=-1; //记录左、右键用的变量。 
   int x=-1,y=-1;        //记录鼠标位置用的变量。
   MyCanvas()
   {  setSize(100,100);
      setBackground(Color.cyan) ;
      addMouseListener(this);
    }   
   public void paint(Graphics g)
   {  if(left==1)
       {  g.drawOval(x-10,y-10,20,20);
       }
     else if(right==1)
       {  g.drawRect(x-8,y-8,16,16);
       }
   } 
   public void mousePressed(MouseEvent e)
   {  x=e.getX(); y=e.getY();
      if(e.getModifiers()==InputEvent.BUTTON1_MASK)
        {  left=1;right=-1;
           repaint();
        }
      else if(e.getModifiers()==InputEvent.BUTTON3_MASK)
       {  right=1; left=-1;
          repaint();
        }
   } 
   public void mouseReleased(MouseEvent e){}
   public void mouseEntered(MouseEvent e){}
   public void mouseExited(MouseEvent e)
   {  left=-1;right=-1;
      repaint();
   }
   public void mouseClicked(MouseEvent e){}
   public void update(Graphics g)
   {  if(left==1||right==1)
        { //paint(g);
        }
      else
        { super.update(g);//改成super.paint(g)亦可
        }
   }
}
public class Example18_2 
{  public static void main(String args[])
   {  Frame f=new Frame();
      f.setBounds(100,100,200,200);f.setVisible(true);
      f.addWindowListener(new WindowAdapter()  //适配器
                  {public void windowClosing(WindowEvent e)
                    {System.exit(0);
                    }
                  });
      f.add(new MyCanvas(),BorderLayout.CENTER);//添加画布。
      f.validate();    
   }
}