001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one or more
003     *  contributor license agreements.  See the NOTICE file distributed with
004     *  this work for additional information regarding copyright ownership.
005     *  The ASF licenses this file to You under the Apache License, Version 2.0
006     *  (the "License"); you may not use this file except in compliance with
007     *  the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     *  Unless required by applicable law or agreed to in writing, software
012     *  distributed under the License is distributed on an "AS IS" BASIS,
013     *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     *  See the License for the specific language governing permissions and
015     *  limitations under the License.
016     */
017    package org.apache.commons.collections.keyvalue;
018    
019    import java.io.Serializable;
020    import java.util.Map;
021    
022    import org.apache.commons.collections.KeyValue;
023    
024    /**
025     * A {@link java.util.Map.Entry Map.Entry} tied to a map underneath.
026     * <p>
027     * This can be used to enable a map entry to make changes on the underlying
028     * map, however this will probably mess up any iterators.
029     *
030     * @since Commons Collections 3.0
031     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
032     * 
033     * @author Stephen Colebourne
034     */
035    public class TiedMapEntry implements Map.Entry, KeyValue, Serializable {
036    
037        /** Serialization version */    
038        private static final long serialVersionUID = -8453869361373831205L;
039    
040        /** The map underlying the entry/iterator */    
041        private final Map map;
042        /** The key */
043        private final Object key;
044    
045        /**
046         * Constructs a new entry with the given Map and key.
047         *
048         * @param map  the map
049         * @param key  the key
050         */
051        public TiedMapEntry(Map map, Object key) {
052            super();
053            this.map = map;
054            this.key = key;
055        }
056    
057        // Map.Entry interface
058        //-------------------------------------------------------------------------
059        /**
060         * Gets the key of this entry
061         * 
062         * @return the key
063         */
064        public Object getKey() {
065            return key;
066        }
067    
068        /**
069         * Gets the value of this entry direct from the map.
070         * 
071         * @return the value
072         */
073        public Object getValue() {
074            return map.get(key);
075        }
076    
077        /**
078         * Sets the value associated with the key direct onto the map.
079         * 
080         * @param value  the new value
081         * @return the old value
082         * @throws IllegalArgumentException if the value is set to this map entry
083         */
084        public Object setValue(Object value) {
085            if (value == this) {
086                throw new IllegalArgumentException("Cannot set value to this map entry");
087            }
088            return map.put(key, value);
089        }
090    
091        /**
092         * Compares this <code>Map.Entry</code> with another <code>Map.Entry</code>.
093         * <p>
094         * Implemented per API documentation of {@link java.util.Map.Entry#equals(Object)}
095         * 
096         * @param obj  the object to compare to
097         * @return true if equal key and value
098         */
099        public boolean equals(Object obj) {
100            if (obj == this) {
101                return true;
102            }
103            if (obj instanceof Map.Entry == false) {
104                return false;
105            }
106            Map.Entry other = (Map.Entry) obj;
107            Object value = getValue();
108            return
109                (key == null ? other.getKey() == null : key.equals(other.getKey())) &&
110                (value == null ? other.getValue() == null : value.equals(other.getValue()));
111        }
112    
113        /**
114         * Gets a hashCode compatible with the equals method.
115         * <p>
116         * Implemented per API documentation of {@link java.util.Map.Entry#hashCode()}
117         * 
118         * @return a suitable hash code
119         */
120        public int hashCode() {
121            Object value = getValue();
122            return (getKey() == null ? 0 : getKey().hashCode()) ^
123                   (value == null ? 0 : value.hashCode()); 
124        }
125    
126        /**
127         * Gets a string version of the entry.
128         * 
129         * @return entry as a string
130         */
131        public String toString() {
132            return getKey() + "=" + getValue();
133        }
134    
135    }