    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}