fontcolor2.java

来自「《java事件处理指南》一书的代码,好东西」· Java 代码 · 共 84 行

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

public class FontColor2
{
   private Color color;
   private PropertyChangeSupport pcs;
   private VetoableChangeSupport vcs;
   private Component parent;

   public FontColor2(Color c, Component p)
   {
/*  The FontColor2 constructor initializes the Color variable as well  */
/*  as a PropertyChangeSupport and VetoableChangeSupport objects.      */
/*  A parent component is passed to the constructor so a JOptionPane   */
/*  can be displayed if a an attempt is made to change the color to    */
/*  a forbidden value.  In this example, the color green is forbidden  */ 

      color = c;
      pcs = new PropertyChangeSupport(this);
      vcs = new VetoableChangeSupport(this);
      parent = p;
   }

   public Color getColor()
   {
      return color;
   }

/*  The Color object is implemented as a constrained property. When  */
/*  the setColor() method is called, the VetoableChangeSupport       */
/*  object fires a PropertyChangeEvent object to any registered      */
/*  VetoableChangeListeners.  These listeners determine if the       */
/*  proposed change is acceptable.  If it is not, a                  */
/*  PropertyVetoException is thrown.  If the change is acceptable,   */
/*  the color instance variable is updated with the change and a     */
/*  PropertyChangeEvent is sent to any registered                    */
/*  PropertyChangeListeners.                                         */

   public void setColor(Color c)
   {
      Color oldColor = color;
      try
      {
         vcs.fireVetoableChange("color", oldColor, c);
         color = c;
      }
      catch (PropertyVetoException pve) 
      {
         JOptionPane.showMessageDialog(parent, pve.getMessage());
      }

      pcs.firePropertyChange("color", oldColor, color);
   }

/*  For the FontColor class to be able to register or de-register      */
/*  a PropertyChangeListener or VetoableChangeListener, it has to      */
/*  provide methods to add and remove those listeners.  The            */
/*  PropertyChangeSupport object is used to manage the                 */
/*  PropertyChangeListener lists and the VetoableChangeSupport object  */
/*  is used to manage the VetoableChangeListener lists.                */

   public void addPropertyChangeListener(PropertyChangeListener listener)
   {
      pcs.addPropertyChangeListener(listener);
   }

   public void removePropertyChangeListener(PropertyChangeListener listener)
   {
      pcs.removePropertyChangeListener(listener);
   }

   public void addVetoableChangeListener(VetoableChangeListener listener)
   {
      vcs.addVetoableChangeListener(listener);
   }

   public void removeVetoableChangeListener(VetoableChangeListener listener)
   {
      vcs.removeVetoableChangeListener(listener);
   }
}