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
024/**
025 * The Hasher allows a {@link java.util.Comparator} implementation to also be delegated to during hashCode generation
026 * during grouping partitioning.
027 * <p>
028 * If a Comparator is used to compare two types during grouping, its likely the {@code hashCode} value between
029 * the two objects will not be consistent. This allows to objects being equal to hash to the same bucket (reducer)
030 * during partitioning.
031 * <p>
032 * As of Cascading 3.0 null values will be passed to implementations of the Hasher interface.
033 */
034public interface Hasher<V>
035  {
036  /**
037   * Return the hashCode of the given value.
038   *
039   * @param value may be null
040   * @return int hashCode of given value
041   */
042  int hashCode( V value );
043  }