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    
015    package org.apache.tapestry.record;
016    
017    import org.apache.hivemind.util.Defense;
018    
019    /**
020     * Used to identify a property change.
021     * 
022     * @author Howard Lewis Ship
023     */
024    
025    public class ChangeKey
026    {
027        private int _hashCode = -1;
028    
029        private String _componentPath;
030    
031        private String _propertyName;
032    
033        public ChangeKey(String componentPath, String propertyName)
034        {
035            Defense.notNull(propertyName, "propertyName");
036    
037            _componentPath = componentPath;
038            _propertyName = propertyName;
039        }
040    
041        public boolean equals(Object object)
042        {
043            if (object == null)
044                return false;
045    
046            if (this == object)
047                return true;
048    
049            if (!(object instanceof ChangeKey))
050                return false;
051    
052            ChangeKey other = (ChangeKey) object;
053    
054            return same(_propertyName, other._propertyName)
055                    && same(_componentPath, other._componentPath);
056        }
057    
058        private boolean same(String s1, String s2)
059        {
060            return s1 == s2 || (s1 != null && s1.equals(s2));
061        }
062    
063        public String getComponentPath()
064        {
065            return _componentPath;
066        }
067    
068        public String getPropertyName()
069        {
070            return _propertyName;
071        }
072    
073        /**
074         * Returns a hash code computed from the property name and component path.
075         */
076    
077        public int hashCode()
078        {
079            if (_hashCode == -1)
080            {
081                _hashCode = 31 * 27 + _propertyName.hashCode();
082    
083                if (_componentPath != null)
084                    _hashCode = 31 * _hashCode + _componentPath.hashCode();
085            }
086    
087            return _hashCode;
088        }
089    }