001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one
003     *  or more contributor license agreements.  See the NOTICE file
004     *  distributed with this work for additional information
005     *  regarding copyright ownership.  The ASF licenses this file
006     *  to you under the Apache License, Version 2.0 (the
007     *  "License"); you may not use this file except in compliance
008     *  with the License.  You may obtain a copy of the License at
009     *  
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *  
012     *  Unless required by applicable law or agreed to in writing,
013     *  software distributed under the License is distributed on an
014     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     *  KIND, either express or implied.  See the License for the
016     *  specific language governing permissions and limitations
017     *  under the License. 
018     *  
019     */
020    
021    package org.apache.directory.shared.ldap.util;
022    
023    
024    import java.util.HashMap;
025    
026    
027    /**
028     * A Map implementation derived from HashMap that only overrides a single method
029     * put() in order to prevent duplicate keyed entries to be added.
030     * 
031     * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
032     * @version $Rev: 437007 $
033     */
034    public class NoDuplicateKeysMap extends HashMap
035    {
036        /**
037         * Overrides java.util.Map.put(java.lang.Object, java.lang.Object) to
038         * prevent duplicate keys.
039         * 
040         * @see java.util.Map#put(java.lang.Object, java.lang.Object)
041         */
042        public Object put( Object key, Object value ) throws IllegalArgumentException
043        {
044            if ( containsKey( key ) )
045            {
046                throw new IllegalArgumentException( "Adding duplicate keys is not permitted." );
047            }
048            else
049            {
050                return super.put( key, value );
051            }
052        }
053    
054        // add a serial version uid, so that if we change things in the future
055        // without changing the format, we can still deserialize properly.
056        private static final long serialVersionUID = 5107433500719957457L;
057    }