    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 *      http://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
    019/**
    020 * An equation function, which determines equality between objects of type T.
    021 * <p>
    022 * It is the functional sibling of {@link java.util.Comparator}; {@link Equator} is to
    023 * {@link Object} as {@link java.util.Comparator} is to {@link Comparable}.
    024 * </p>
    025 *
    026 * @param <T> the types of object this {@link Equator} can evaluate.
    027 * @since 4.0
    028 */
    029public interface Equator<T> {
    030    /**
    031     * Evaluates the two arguments for their equality.
    032     *
    033     * @param o1 the first object to be equated.
    034     * @param o2 the second object to be equated.
    035     * @return whether the two objects are equal.
    036     */
    037    boolean equate(T o1, T o2);
    038
    039    /**
    040     * Calculates the hash for the object, based on the method of equality used in the equate
    041     * method. This is used for classes that delegate their {@link Object#equals(Object) equals(Object)} method to an
    042     * Equator (and so must also delegate their {@link Object#hashCode() hashCode()} method), or for implementations
    043     * of {@link org.apache.commons.collections4.map.HashedMap} that use an Equator for the key objects.
    044     *
    045     * @param o the object to calculate the hash for.
    046     * @return the hash of the object.
    047     */
    048    int hash(T o);
    049}