    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      }