001/*
002 * Copyright (c) 2007-2016 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
021package cascading.tuple;
022
023import 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 */
040public interface Comparison<T>
041  {
042  Comparator<T> getComparator( Class<T> type );
043  }