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.numbers.core;
18
19 /**
20 * Multiplication.
21 *
22 * @param <T> Type of elements.
23 */
24 public interface Multiplication<T> {
25 /**
26 * Binary multiplication.
27 *
28 * @param a Element.
29 * @return {@code this * a}.
30 */
31 T multiply(T a);
32
33 /**
34 * Identity element.
35 *
36 * @return the field element such that for all {@code a},
37 * {@code one().multiply(a).equals(a)} is {@code true}.
38 */
39 T one();
40
41 /**
42 * Multiplicative inverse.
43 *
44 * @return <code>this<sup>-1</sup></code>.
45 */
46 T reciprocal();
47
48 /**
49 * Check if this is a neutral element of multiplication, i.e. {@code this.multiply(a)} returns
50 * {@code a} or an element representing the same value as {@code a}.
51 *
52 * <p>The default implementation calls {@link Object#equals(Object) equals(one())}.
53 * Implementations may want to employ more a efficient method. This may even
54 * be required if an implementation has multiple representations of {@code one} and its
55 * {@code equals} method differentiates between them.
56 *
57 * @return {@code true} if {@code this} is a neutral element of multiplication.
58 * @see #one()
59 * @since 1.2
60 */
61 default boolean isOne() {
62 return this.equals(one());
63 }
64 }