Logo Search packages:      
Sourcecode: libjgoodies-binding-java version File versions

ExtendedPropertyChangeSupport.java

/*
 * Copyright (c) 2002-2007 JGoodies Karsten Lentzsch. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 *  o Redistributions of source code must retain the above copyright notice, 
 *    this list of conditions and the following disclaimer. 
 *     
 *  o Redistributions in binary form must reproduce the above copyright notice, 
 *    this list of conditions and the following disclaimer in the documentation 
 *    and/or other materials provided with the distribution. 
 *     
 *  o Neither the name of JGoodies Karsten Lentzsch nor the names of 
 *    its contributors may be used to endorse or promote products derived 
 *    from this software without specific prior written permission. 
 *     
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR 
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE 
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

package com.jgoodies.binding.beans;

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeListenerProxy;
import java.beans.PropertyChangeSupport;

/**
 * Differs from its superclass {@link PropertyChangeSupport} in that it can
 * check for changed values using <code>#equals</code> or <code>==</code>.
 * Useful if you want to ensure that a <code>PropertyChangeEvent</code> is fired
 * if the old and new value are not the same but if they are equal.<p>
 * 
 * The <a href="http://java.sun.com/products/javabeans/docs/spec.html">Java 
 * Bean Secification</a> <em>recommends</em> to not throw a 
 * PropertyChangeEvent if the old and new value of a bound
 * Bean property are equal (see chapter 7.4.4). This can reduce the number
 * of events fired and helps avoid loops. Nevertheless a bound property 
 * <em>may</em> fire an event if the old and new value are equal.<p>
 * 
 * An example for a condition where the identity check <code>==</code>
 * is required and the <code>#equals</code> test fails is class 
 * {@link com.jgoodies.binding.list.SelectionInList}. If the contained
 * <code>ListModel</code> changes its value, an internal listener is removed 
 * from the old value and added to the new value. The listener must be
 * moved from the old instance to the new instance even if these are equal.
 * The <code>PropertyChangeSupport</code> doesn't fire a property change event
 * if such a <code>ListModel</code> is implemented as a {@link java.util.List}.
 * This is because instances of <code>List</code> are equal if and only if 
 * all list members are equal and if they are in the same sequence.<p>
 * 
 * This class provides two means to fire an event if the old and new
 * value are equal but not the same. First, you enable the identity check
 * in constructor {@link #ExtendedPropertyChangeSupport(Object, boolean)}.
 * By default all calls to <code>#firePropertyChange</code> will then
 * check the identity, not the equality. Second, you can invoke
 * {@link #firePropertyChange(PropertyChangeEvent, boolean)} or
 * {@link #firePropertyChange(String, Object, Object, boolean)} and
 * enable or disable the identity check for this call only.<p>
 * 
 * TODO: (Issue #5) Use WeakReferences to refer to registered listeners.<p>
 * 
 * TODO: (Issue #6) Add an optional check for valid property name 
 * when adding a listener for a specific property.<p>
 * 
 * TODO: (Issue #7) Add an optional strict check for existing 
 * property names when firing a named property change.<p>
 * 
 * TODO: (Issue #8) Add an option to ensure that update notifications
 * are performed in the event dispatch thread. In case a bean 
 * is changed in a thread other than the event dispatch thread, such 
 * a feature would help complying with Swing's single thread rule.<p>
 * 
 * TODO: (Issue #11) Consider adding an option that saves update notifications
 * if 'checkIdentity' is true but the value types can be compared
 * safely via #equals, for example Strings, Booleans and Numbers. 
 * 
 * @author <a href="mailto:neuling@dakosy.de">Mattias Neuling</a>
 * @author Karsten Lentzsch
 * @version $Revision: 1.4 $
 * 
 * @see PropertyChangeSupport
 * @see PropertyChangeEvent
 * @see PropertyChangeListener
 * @see Object#equals(Object)
 * @see java.util.List#equals(Object)
 */
00098 public final class ExtendedPropertyChangeSupport extends PropertyChangeSupport {
    
    /** 
     * The object to be provided as the "source" for any generated events.
     * @serial
     */
00104     private final Object source;
    
    /**
     * The default setting for the identity check. 
     * Can be overridden by the #firePropertyChange methods
     * that accept a <code>checkIdentity</code> parameter.
     */
00111     private final boolean checkIdentityDefault;
    
    
    // Instance Creation ******************************************************

    /**
     * Constructs an <code>ExtendedPropertyChangeSupport</code> object.
     *
     * @param sourceBean  The bean to be given as the source for any events.
     */
00121     public ExtendedPropertyChangeSupport(Object sourceBean) {
        this(sourceBean, false);
    }
    
    /**
     * Constructs an <code>ExtendedPropertyChangeSupport</code> object
     * with the specified default test method for differences between
     * the old and new property values.
     *
     * @param sourceBean  The object provided as the source for any generated events.
     * @param checkIdentityDefault true enables the identity check by default
     */
00133     public ExtendedPropertyChangeSupport(
        Object sourceBean,
        boolean checkIdentityDefault) {
        super(sourceBean);
        this.source = sourceBean;
        this.checkIdentityDefault = checkIdentityDefault;
    }
    
    
    // Firing Events **********************************************************

    /**
     * Fires the specified PropertyChangeEvent to any registered listeners.
     * Uses the default test (<code>#equals</code> vs. <code>==</code>) 
     * to determine whether the event's old and new values are different.
     * No event is fired if old and new value are the same.
     * 
     * @param evt  The PropertyChangeEvent object.
     * 
     * @see PropertyChangeSupport#firePropertyChange(PropertyChangeEvent)
     */
00154     public void firePropertyChange(PropertyChangeEvent evt) {
        firePropertyChange(evt, checkIdentityDefault);
    }
    

    /**
     * Reports a bound property update to any registered listeners.
     * Uses the default test (<code>#equals</code> vs. <code>==</code>) 
     * to determine whether the event's old and new values are different.
     * No event is fired if old and new value are the same.
     *
     * @param propertyName  The programmatic name of the property
     *      that was changed.
     * @param oldValue  The old value of the property.
     * @param newValue  The new value of the property.
     * 
     * @see PropertyChangeSupport#firePropertyChange(String, Object, Object)
     */
00172     public void firePropertyChange(
        String propertyName,
        Object oldValue,
        Object newValue) {
        firePropertyChange(propertyName, oldValue, newValue, checkIdentityDefault);
    }
    

    /**
     * Fires an existing PropertyChangeEvent to any registered listeners.
     * The boolean parameter specifies whether differences between the old 
     * and new value are tested using <code>==</code> or <code>#equals</code>.
     * No event is fired if old and new value are the same.
     * 
     * @param evt  The PropertyChangeEvent object.
     * @param checkIdentity  true to check differences using <code>==</code>
     *     false to use <code>#equals</code>.
     */
00190     public void firePropertyChange(PropertyChangeEvent evt, boolean checkIdentity) {
        Object oldValue = evt.getOldValue();
        Object newValue = evt.getNewValue();
        if (oldValue != null && oldValue == newValue) {
            return;
        } else if (checkIdentity) {
            fireUnchecked(evt);
        } else {
            super.firePropertyChange(evt);
        }
    }
    

    /**
     * Reports a bound property update to any registered listeners.
     * No event is fired if the old and new value are the same.
     * If checkIdentity is <code>true</code> an event is fired in all
     * other cases. If this parameter is <code>false</code>, an event is fired
     * if old and new values are not equal.
     * 
     * @param propertyName  The programmatic name of the property
     *      that was changed.
     * @param oldValue  The old value of the property.
     * @param newValue  The new value of the property.
     * @param checkIdentity  true to check differences using <code>==</code>
     *     false to use <code>#equals</code>.
     */
00217     public void firePropertyChange(
        String propertyName,
        Object oldValue,
        Object newValue,
        boolean checkIdentity) {

        if (oldValue != null && oldValue == newValue) {
            return;
        } else if (checkIdentity) {
            fireUnchecked(
                new PropertyChangeEvent(
                    source,
                    propertyName,
                    oldValue,
                    newValue));
        } else {
            super.firePropertyChange(propertyName, oldValue, newValue);
        }
    }

    
    /**
     * Fires a PropertyChangeEvent to all its listeners without checking via
     * equals method if the old value is equal to new value. The instance
     * equality check is done by the calling firePropertyChange method
     * (to avoid instance creation of the PropertyChangeEvent).<p>
     * 
     * If some listeners have been added with a named property, then
     * <code>PropertyChangeSupport#getPropertyChangeListeners()</code> returns
     * an array with a mixture of PropertyChangeListeners
     * and <code>PropertyChangeListenerProxy</code>s. We notify all non-proxies
     * and those proxies that have a property name that is equals to the
     * event's property name.
     * 
     * @param evt event to fire to the listeners
     * 
     * @see PropertyChangeListenerProxy
     * @see PropertyChangeSupport#getPropertyChangeListeners()
     */
00256     private void fireUnchecked(PropertyChangeEvent evt) {
        PropertyChangeListener[] listeners;
        synchronized (this) {
            listeners = getPropertyChangeListeners();
        }
        String propertyName = evt.getPropertyName();
        for (int i = 0; i < listeners.length; i++) {
            PropertyChangeListener listener = listeners[i];
            if (listener instanceof PropertyChangeListenerProxy) {
                PropertyChangeListenerProxy proxy = 
                    (PropertyChangeListenerProxy) listener;
                if (proxy.getPropertyName().equals(propertyName)) {
                    proxy.propertyChange(evt);
                }
            } else {
                listener.propertyChange(evt);
            }
        }
    }

}

Generated by  Doxygen 1.6.0   Back to index