001// Copyright 2004, 2005 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007//     http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry.event;
016
017/**
018 * May observe changes in an object's properties.  This is a "weak" variation
019 * on JavaBean's style bound properties.  It is used when there will be at most
020 * a single listener on property changes, and that the listener is not interested
021 * in the old value.
022 *
023 * @author Howard Lewis Ship
024 * 
025 **/
026
027public interface ChangeObserver
028{
029    /**
030     *  Sent when the observed object changes a property.  The event identifies
031     *  the object, the property and the new value.
032     *
033     **/
034
035    public void observeChange(ObservedChangeEvent event);
036}