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 * http://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 /**
20 * An equation function, which determines equality between objects of type T.
21 * <p>
22 * It is the functional sibling of {@link java.util.Comparator}; {@link Equator} is to
23 * {@link Object} as {@link java.util.Comparator} is to {@link Comparable}.
24 * </p>
25 *
26 * @param <T> the types of object this {@link Equator} can evaluate.
27 * @since 4.0
28 */
29 public interface Equator<T> {
30 /**
31 * Evaluates the two arguments for their equality.
32 *
33 * @param o1 the first object to be equated.
34 * @param o2 the second object to be equated.
35 * @return whether the two objects are equal.
36 */
37 boolean equate(T o1, T o2);
38
39 /**
40 * Calculates the hash for the object, based on the method of equality used in the equate
41 * method. This is used for classes that delegate their {@link Object#equals(Object) equals(Object)} method to an
42 * Equator (and so must also delegate their {@link Object#hashCode() hashCode()} method), or for implementations
43 * of {@link org.apache.commons.collections4.map.HashedMap} that use an Equator for the key objects.
44 *
45 * @param o the object to calculate the hash for.
46 * @return the hash of the object.
47 */
48 int hash(T o);
49 }