001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4;
018
019import java.util.Comparator;
020
021import org.apache.commons.collections4.map.HashedMap;
022/**
023 * An equation function, which determines equality between objects of type T.
024 * <p>
025 * It is the functional sibling of {@link Comparator}; {@link Equator} is to
026 * {@link Object} as {@link Comparator} is to {@link Comparable}.
027 * </p>
028 *
029 * @param <T> The types of object this {@link Equator} can evaluate.
030 * @since 4.0
031 */
032public interface Equator<T> {
033
034    /**
035     * Evaluates the two arguments for their equality.
036     *
037     * @param o1 The first object to be equated.
038     * @param o2 The second object to be equated.
039     * @return whether the two objects are equal.
040     */
041    boolean equate(T o1, T o2);
042
043    /**
044     * Calculates the hash for the object, based on the method of equality used in the equate
045     * method. This is used for classes that delegate their {@link Object#equals(Object) equals(Object)} method to an
046     * Equator (and so must also delegate their {@link Object#hashCode() hashCode()} method), or for implementations
047     * of {@link HashedMap} that use an Equator for the key objects.
048     *
049     * @param o The object to calculate the hash for.
050     * @return The hash of the object.
051     */
052    int hash(T o);
053}