001    /*--------------------------------------------------------------------------+
002    $Id: IdComparator.java 26283 2010-02-18 11:18:57Z juergens $
003    |                                                                          |
004    | Copyright 2005-2010 Technische Universitaet Muenchen                     |
005    |                                                                          |
006    | Licensed under the Apache License, Version 2.0 (the "License");          |
007    | you may not use this file except in compliance with the License.         |
008    | 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, software      |
013    | distributed under the License is distributed on an "AS IS" BASIS,        |
014    | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
015    | See the License for the specific language governing permissions and      |
016    | limitations under the License.                                           |
017    +--------------------------------------------------------------------------*/
018    package edu.tum.cs.commons.collections;
019    
020    /**
021     * Comparator that compares objects based on the identifiers provided by a
022     * {@link IIdProvider}.
023     * 
024     * @author deissenb
025     * @author $Author: juergens $
026     * @version $Rev: 26283 $
027     * @levd.rating GREEN Hash: 3F2D6549B37B7E5FF4BC2F5E98EC0A29
028     */
029    public class IdComparator<I extends Comparable<I>, T> extends
030                    IdentifierBasedComparatorBase<I, T> {
031    
032            /** ID provider used for comparing. */
033            private final IIdProvider<I, T> idProvider;
034    
035            /** Create new comparator. */
036            public IdComparator(IIdProvider<I, T> idProvider) {
037                    this.idProvider = idProvider;
038            }
039    
040            /**
041             * Obtain identifier from identifier provider.
042             * 
043             * @throws NullPointerException
044             *             if the id provider returns <code>null</code>.
045             */
046            @Override
047            protected I obtainIdentifier(T t) {
048                    I id = idProvider.obtainId(t);
049                    if (id == null) {
050                            throw new NullPointerException("Id for " + t + " is null.");
051                    }
052                    return id;
053            }
054    }