001 /*
002 * Java Genetic Algorithm Library (jenetics-4.4.0).
003 * Copyright (c) 2007-2019 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * 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 *
017 * Author:
018 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020 package io.jenetics.prog.op;
021
022 import static java.util.Objects.requireNonNull;
023 import static io.jenetics.internal.util.Hashes.hash;
024
025 import java.io.Serializable;
026 import java.util.Objects;
027
028 /**
029 * Represents an operation which always returns the same, constant, value. To
030 * improve readability, constants may have a name. If a name is given, this name
031 * is used when printing the program tree. The {@code Const} operation is a
032 * <em>terminal</em> operation.
033 *
034 * <pre>{@code
035 * final static Op<Double> PI = Const.of("π", Math.PI);
036 * final static Op<Double> ONE = Const.of(1.0);
037 * }</pre>
038 *
039 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
040 * @version 4.1
041 * @since 3.9
042 */
043 public final class Const<T> implements Op<T>, Serializable {
044
045 private static final long serialVersionUID = 1L;
046
047 private final String _name;
048 private final T _const;
049
050 private Const(final String name, final T constant) {
051 _name = name;
052 _const = constant;
053 }
054
055 @Override
056 public T apply(final T[] value) {
057 return _const;
058 }
059
060 /**
061 * Return the constant value.
062 *
063 * @since 4.1
064 *
065 * @return the constant value
066 */
067 public T value() {
068 return _const;
069 }
070
071 @Override
072 public String name() {
073 return _name;
074 }
075
076 @Override
077 public int arity() {
078 return 0;
079 }
080
081 @Override
082 public int hashCode() {
083 return hash(_name, hash(_const));
084 }
085
086 @Override
087 public boolean equals(final Object obj) {
088 return obj == this ||
089 obj instanceof Const &&
090 Objects.equals(((Const)obj)._name, _name) &&
091 equal(((Const)obj)._const, _const);
092 }
093
094 private static boolean equal(final Object a, final Object b) {
095 if (a instanceof Double && b instanceof Double) {
096 return ((Double)a).doubleValue() == ((Double)b).doubleValue();
097 } else if (a instanceof Float && b instanceof Float) {
098 return ((Float)a).floatValue() == ((Float)b).floatValue();
099 }
100
101 return Objects.equals(a, b);
102 }
103
104 @Override
105 public String toString() {
106 return _name != null ? _name : Objects.toString(_const);
107 }
108
109 /**
110 * Return a new constant with the given name and value.
111 *
112 * @param name the constant name
113 * @param value the constant value
114 * @param <T> the constant type
115 * @return a new constant
116 * @throws NullPointerException if the given constant {@code name} is
117 * {@code null}
118 */
119 public static <T> Const<T> of(final String name, final T value) {
120 return new Const<>(requireNonNull(name), value);
121 }
122
123 /**
124 * Return a new constant with the given value.
125 *
126 * @param value the constant value
127 * @param <T> the constant type
128 * @return a new constant
129 */
130 public static <T> Const<T> of(final T value) {
131 return new Const<>(null, value);
132 }
133
134 }
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