001/*
002 * Copyright (c) 2007-2017 Xplenty, 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
023/**
024 * The Hasher allows a {@link java.util.Comparator} implementation to also be delegated to during hashCode generation
025 * during grouping partitioning.
026 * <p/>
027 * If a Comparator is used to compare two types during grouping, its likely the {@code hashCode} value between
028 * the two objects will not be consistent. This allows to objects being equal to hash to the same bucket (reducer)
029 * during partitioning.
030 * <p/>
031 * As of Cascading 3.0 null values will be passed to implementations of the Hasher interface.
032 */
033public interface Hasher<V>
034  {
035  /**
036   * Return the hashCode of the given value.
037   *
038   * @param value may be null
039   * @return int hashCode of given value
040   */
041  int hashCode( V value );
042  }