001 /*
002 * Java Genetic Algorithm Library (jenetics-4.3.0).
003 * Copyright (c) 2007-2018 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.lang.String.format;
023 import static java.util.Objects.requireNonNull;
024 import static io.jenetics.internal.util.Hashes.hash;
025
026 import java.io.Serializable;
027 import java.util.Objects;
028 import java.util.function.Supplier;
029
030 import io.jenetics.internal.util.Lazy;
031
032 /**
033 * Implementation of an <em>ephemeral</em> constant. It causes the insertion of
034 * a <em>mutable</em> constant into the operation tree. Every time this terminal
035 * is chosen a, different value is generated which is then used for that
036 * particular terminal, and which will remain fixed for the given tree. The main
037 * usage would be to introduce random terminal values.
038 *
039 * <pre>{@code
040 * final Random random = ...;
041 * final Op<Double> val = EphemeralConst.of(random::nextDouble());
042 * }</pre>
043 *
044 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
045 * @version 4.1
046 * @since 3.9
047 */
048 public final class EphemeralConst<T> implements Op<T>, Serializable {
049
050 private static final long serialVersionUID = 1L;
051
052 private final String _name;
053 private final Supplier<T> _supplier;
054 private final Lazy<T> _value;
055
056 private EphemeralConst(final String name, final Supplier<T> supplier) {
057 _name = name;
058 _supplier = requireNonNull(supplier);
059 _value = Lazy.of(_supplier);
060 }
061
062 @Override
063 public String name() {
064 return _name;
065 }
066
067 @Override
068 public int arity() {
069 return 0;
070 }
071
072 /**
073 * Return a newly created, uninitialized constant of type {@code T}.
074 *
075 * @return a newly created, uninitialized constant of type {@code T}
076 */
077 @Override
078 public Op<T> get() {
079 return new EphemeralConst<>(_name, _supplier);
080 }
081
082 @Override
083 public T apply(final T[] ts) {
084 return _value.get();
085 }
086
087 @Override
088 public int hashCode() {
089 return hash(_name, hash(_value));
090 }
091
092 @Override
093 public boolean equals(final Object obj) {
094 return obj == this ||
095 obj instanceof EphemeralConst &&
096 Objects.equals(((EphemeralConst)obj)._name, _name) &&
097 Objects.equals(((EphemeralConst)obj)._value, _value);
098 }
099
100 @Override
101 public String toString() {
102 return _name != null
103 ? format("%s(%s)", _name, _value.get())
104 : Objects.toString(_value.get());
105 }
106
107 /**
108 * Create a new ephemeral constant with the given {@code name} and value
109 * {@code supplier}. For every newly created operation tree, a new constant
110 * value is chosen for this terminal operation. The value is than kept
111 * constant for this tree.
112 *
113 * @param name the name of the ephemeral constant
114 * @param supplier the value supplier
115 * @param <T> the constant type
116 * @return a new ephemeral constant
117 * @throws NullPointerException if one of the arguments is {@code null}
118 */
119 public static <T> EphemeralConst<T> of(
120 final String name,
121 final Supplier<T> supplier
122 ) {
123 return new EphemeralConst<>(requireNonNull(name), supplier);
124 }
125
126 /**
127 * Create a new ephemeral constant with the given value {@code supplier}.
128 * For every newly created operation tree, a new constant value is chosen
129 * for this terminal operation. The value is than kept constant for this tree.
130 *
131 * @param supplier the value supplier
132 * @param <T> the constant type
133 * @return a new ephemeral constant
134 * @throws NullPointerException if the {@code supplier} is {@code null}
135 */
136 public static <T> EphemeralConst<T> of(final Supplier<T> supplier) {
137 return new EphemeralConst<>(null, supplier);
138 }
139
140 }
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