1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections4;
18
19 import java.util.Comparator;
20
21 import org.apache.commons.collections4.map.HashedMap;
22 /**
23 * An equation function, which determines equality between objects of type T.
24 * <p>
25 * It is the functional sibling of {@link Comparator}; {@link Equator} is to
26 * {@link Object} as {@link Comparator} is to {@link Comparable}.
27 * </p>
28 *
29 * @param <T> The types of object this {@link Equator} can evaluate.
30 * @since 4.0
31 */
32 public interface Equator<T> {
33
34 /**
35 * Evaluates the two arguments for their equality.
36 *
37 * @param o1 The first object to be equated.
38 * @param o2 The second object to be equated.
39 * @return whether the two objects are equal.
40 */
41 boolean equate(T o1, T o2);
42
43 /**
44 * Calculates the hash for the object, based on the method of equality used in the equate
45 * method. This is used for classes that delegate their {@link Object#equals(Object) equals(Object)} method to an
46 * Equator (and so must also delegate their {@link Object#hashCode() hashCode()} method), or for implementations
47 * of {@link HashedMap} that use an Equator for the key objects.
48 *
49 * @param o The object to calculate the hash for.
50 * @return The hash of the object.
51 */
52 int hash(T o);
53 }