001/*
002 * Copyright (c) 2016-2017 Chris K Wensel <chris@wensel.net>. All Rights Reserved.
003 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
004 *
005 * Project and contact information: http://www.cascading.org/
006 *
007 * This file is part of the Cascading project.
008 *
009 * Licensed under the Apache License, Version 2.0 (the "License");
010 * you may not use this file except in compliance with the License.
011 * You may obtain a copy of the License at
012 *
013 *     http://www.apache.org/licenses/LICENSE-2.0
014 *
015 * Unless required by applicable law or agreed to in writing, software
016 * distributed under the License is distributed on an "AS IS" BASIS,
017 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
018 * See the License for the specific language governing permissions and
019 * limitations under the License.
020 */
021
022package cascading.tuple;
023
024import java.util.Comparator;
025
026/**
027 * The Comparison interface allows specific underlying type mechanisms to additionally return relevant
028 * {@link Comparator} implementations when required internally.
029 * <p>
030 * In the case of Hadoop, {@link org.apache.hadoop.io.serializer.Serialization} implementations that present
031 * alternative serialization implementations for custom types manged by {@link Tuple}s should also
032 * implement the {@link #getComparator(Class)} method.
033 * <p>
034 * During runtime Cascading can identify and use the correct Comparator during grouping operations if it was
035 * not given explicitly on the {@link Fields#setComparator(Comparable, java.util.Comparator)} family of methods.
036 * <p>
037 * See the class {@link cascading.tuple.hadoop.BytesSerialization} for an example.
038 * <p>
039 * see cascading.tuple.hadoop.BytesSerialization
040 */
041public interface Comparison<T>
042  {
043  Comparator<T> getComparator( Class<T> type );
044  }