vetoablechangedemo.java

《java事件处理指南》一书的代码,好东西

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

public class VetoableChangeDemo extends JFrame implements ItemListener
{
   NewLabel2 label1, label2, label3; 
   FontColor2 fontColor;
   JComboBox jcb;

   public VetoableChangeDemo()
   {
/*  A FontColor2 object is created.  This object maintains a Color   */
/*  object as a constrained property.                                */

      fontColor = new FontColor2(Color.black, this);

/*  Three NewLabel objects are created and placed on a JFrame.  The  */
/*  NewLabel class is a JLabel that uses a FontColor object to set   */
/*  the color of the label text.                                     */

      label1 = new NewLabel2("hello", fontColor);
      label1.setFont(new Font("Serif", Font.BOLD, 14));

      label2 = new NewLabel2("there", fontColor);
      label2.setFont(new Font("Serif", Font.BOLD, 14));

      label3 = new NewLabel2("boys", fontColor);
      label3.setFont(new Font("Serif", Font.BOLD, 14));

/*  A JComboBox is used to change the color of the NewLabel object text  */
/*  The JComboBox registers an ItemListener.                             */

      String[] colorList = {"black", "red", "blue", "green"};
      jcb = new JComboBox(colorList);
      jcb.setSelectedIndex(0);
      jcb.addItemListener(this);

      JPanel centerPanel = new JPanel();
      centerPanel.add(label1);
      centerPanel.add(label2);
      centerPanel.add(label3);

      JPanel southPanel = new JPanel();
      southPanel.add(jcb);

      getContentPane().add(centerPanel, BorderLayout.CENTER);
      getContentPane().add(southPanel, BorderLayout.WEST);

      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setBounds(100, 100, 300, 200);
      setVisible(true);
   }

/*  Since the VetoableChangeDemo class serves as the ItemListener,    */
/*  it provides an implementation of the itemStateChanged() method.   */
/*  The FontColor2 object calls its setColor() method passing it the   */
/*  selected color.                                                   */

   public void itemStateChanged(ItemEvent event)
   {
      JComboBox comboBox = (JComboBox)event.getItemSelectable();
      String color = (String)comboBox.getSelectedItem();
      if ( color.equals("black") ) 
             fontColor.setColor(Color.black); 
      if ( color.equals("red") ) 
             fontColor.setColor(Color.red); 
      if ( color.equals("blue") ) 
             fontColor.setColor(Color.blue); 
      if ( color.equals("green") ) 
             fontColor.setColor(Color.green); 

/*  If the color change is vetoed, the label text color is reset to   */
/*  its previous value.  This next block of code insures that the     */
/*  current selection of the JComboBox will be reset as well.         */

      Color c = fontColor.getColor();
      if ( c.equals(Color.black) )
           comboBox.setSelectedIndex(0);
      if ( c.equals(Color.red) )
           comboBox.setSelectedIndex(1);
      if ( c.equals(Color.blue) )
           comboBox.setSelectedIndex(2);
      if ( c.equals(Color.green) )
           comboBox.setSelectedIndex(3);
   }

   public static void main(String args[])
   {
      VetoableChangeDemo demo = new VetoableChangeDemo();
   }
}