popupmenudemo.java

这是孙卫琴在"Java与面向对象编程"一书的源代码。

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class PopupMenuDemo extends JFrame {
  private String[] colorNames = { "Blue", "Yellow", "Red" };
  private Color[] colors = { Color.BLUE, Color.YELLOW, Color.RED };
  private JRadioButtonMenuItem items[];
  private JPopupMenu popupMenu = new JPopupMenu();
  
  private ActionListener itemHandler=new ActionListener(){  //处理菜单项的事件
    public void actionPerformed( ActionEvent e ){
      for ( int i = 0; i < items.length; i++ )
          if ( e.getSource() == items[ i ] ) {  //判断用户选择了哪个菜单项
             getContentPane().setBackground(colors[ i ] );
             repaint();
             return;
          }
    }
  };

  public PopupMenuDemo(String title) {
    super(title);

     ButtonGroup colorGroup = new ButtonGroup();
     items = new JRadioButtonMenuItem[ 3 ];

      for ( int i = 0; i < items.length; i++ ) {
         items[ i ] = new JRadioButtonMenuItem( colorNames[ i ] );
         popupMenu.add( items[ i ] );
         colorGroup.add( items[ i ] );
         items[ i ].addActionListener( itemHandler );
      }

      getContentPane().setBackground( Color.WHITE );

      addMouseListener( new MouseAdapter() {
          public void mousePressed( MouseEvent e){checkForTriggerEvent( e ); }
          public void mouseReleased( MouseEvent e){ checkForTriggerEvent( e ); }
          private void checkForTriggerEvent( MouseEvent e){
             if ( e.isPopupTrigger() )  //弹出菜单
                popupMenu.show( e.getComponent(),e.getX(), e.getY() );
          }
        }
      );

      setSize( 500, 200 );
      setVisible( true );
      setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }

   public static void main( String args[] ){
      new PopupMenuDemo("Hello");
   }
}


/****************************************************
 * 作者：孙卫琴                                     *
 * 来源：<<Java面向对象编程>>                       *
 * 技术支持网址：www.javathinker.org                *
 ***************************************************/