001    /*
002     * Copyright (c) 2007-2014 Concurrent, Inc. All Rights Reserved.
003     *
004     * Project and contact information: http://www.cascading.org/
005     *
006     * This file is part of the Cascading project.
007     *
008     * Licensed under the Apache License, Version 2.0 (the "License");
009     * you may not use this file except in compliance with the License.
010     * You may obtain a copy of the License at
011     *
012     *     http://www.apache.org/licenses/LICENSE-2.0
013     *
014     * Unless required by applicable law or agreed to in writing, software
015     * distributed under the License is distributed on an "AS IS" BASIS,
016     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017     * See the License for the specific language governing permissions and
018     * limitations under the License.
019     */
020    
021    package cascading.tuple;
022    
023    import java.util.Comparator;
024    
025    /**
026     * The Comparison interface allows specific underlying type mechanisms to additionally return relevant
027     * {@link Comparator} implementations when required internally.
028     * <p/>
029     * In the case of Hadoop, {@link org.apache.hadoop.io.serializer.Serialization} implementations that present
030     * alternative serialization implementations for custom types manged by {@link Tuple}s should also
031     * implement the {@link #getComparator(Class)} method.
032     * <p/>
033     * During runtime Cascading can identify and use the correct Comparator during grouping operations if it was
034     * not given explicitly on the {@link Fields#setComparator(Comparable, java.util.Comparator)} family of methods.
035     * <p/>
036     * See the class {@link cascading.tuple.hadoop.BytesSerialization} for an example.
037     * <p/>
038     * see cascading.tuple.hadoop.BytesSerialization
039     */
040    public interface Comparison<T>
041      {
042      Comparator<T> getComparator( Class<T> type );
043      }