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