001 /*
002 * Java Genetic Algorithm Library (jenetics-7.1.0).
003 * Copyright (c) 2007-2022 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.SerialIO.readNullableString;
025 import static io.jenetics.internal.util.SerialIO.writeNullableString;
026
027 import java.io.IOException;
028 import java.io.InvalidObjectException;
029 import java.io.ObjectInput;
030 import java.io.ObjectInputStream;
031 import java.io.ObjectOutput;
032 import java.io.Serial;
033 import java.io.Serializable;
034 import java.util.Objects;
035 import java.util.function.Supplier;
036
037 import io.jenetics.internal.util.Lazy;
038
039 /**
040 * Implementation of an <em>ephemeral</em> constant. It causes the insertion of
041 * a <em>mutable</em> constant into the operation tree. Every time this terminal
042 * is chosen a, different value is generated which is then used for that
043 * particular terminal, and which will remain fixed for the given tree. The main
044 * usage would be to introduce random terminal values.
045 *
046 * <pre>{@code
047 * final Random random = ...;
048 * final Op<Double> val = EphemeralConst.of(random::nextDouble);
049 * }</pre>
050 *
051 * <b>Serialization</b>
052 * Although the {@code EphemeralConst} class implements the {@link Serializable}
053 * interface, the serialization will fail if the <em>const</em> supplier is not
054 * <em>serializable</em> as well. This can be achieved by <em>casting</em> the
055 * supplier to a {@link Serializable}.
056 * <pre>{@code
057 * final Random random = new Random();
058 * final EphemeralConst<Integer> object = EphemeralConst.of(
059 * "R",
060 * (Supplier<Integer> & Serializable)random::nextInt
061 * );
062 * }</pre>
063 * The serialization of the <em>constant</em> will fail, if the lambda has to
064 * capture variables form a <em>non</em>-serializable context (class). In such a
065 * case it is advisable to create a dedicated supplier class.
066 * <pre>{@code
067 * final class RandomInt implements Supplier<Integer>, Serializable {
068 * private final Random rnd = new Random();
069 * private final int min;
070 * private final int max;
071 *
072 * private RandomInt(final int min, final int max) {
073 * this.min = min;
074 * this.max = max;
075 * }
076 *
077 * \@Override
078 * public Integer get() {
079 * return rnd.nextInt(max - min) + min;
080 * }
081 * }
082 * }</pre>
083 *
084 *
085 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
086 * @version 7.0
087 * @since 3.9
088 */
089 public final class EphemeralConst<T>
090 extends Val<T>
091 implements Op<T>, Serializable
092 {
093
094 @Serial
095 private static final long serialVersionUID = 1L;
096
097 private final Lazy<T> _value;
098 private final Supplier<T> _supplier;
099
100 private EphemeralConst(
101 final String name,
102 final Lazy<T> value,
103 final Supplier<T> supplier
104 ) {
105 super(name);
106 _value = requireNonNull(value);
107 _supplier = requireNonNull(supplier);
108 }
109
110 private EphemeralConst(final String name, final Supplier<T> supplier) {
111 this(name, Lazy.of(supplier), supplier);
112 }
113
114 /**
115 * Return a newly created, uninitialized constant of type {@code T}.
116 *
117 * @return a newly created, uninitialized constant of type {@code T}
118 */
119 @Override
120 public Op<T> get() {
121 return new EphemeralConst<>(name(), _supplier);
122 }
123
124 /**
125 * Fixes and returns the constant value.
126 *
127 * @since 5.0
128 *
129 * @return the constant value
130 */
131 @Override
132 public T value() {
133 return _value.get();
134 }
135
136 @Override
137 public String toString() {
138 return name() != null
139 ? format("%s(%s)", name(), value())
140 : Objects.toString(value());
141 }
142
143 /**
144 * Create a new ephemeral constant with the given {@code name} and value
145 * {@code supplier}. For every newly created operation tree, a new constant
146 * value is chosen for this terminal operation. The value is than kept
147 * constant for this tree.
148 *
149 * @param name the name of the ephemeral constant
150 * @param supplier the value supplier
151 * @param <T> the constant type
152 * @return a new ephemeral constant
153 * @throws NullPointerException if one of the arguments is {@code null}
154 */
155 public static <T> EphemeralConst<T> of(
156 final String name,
157 final Supplier<T> supplier
158 ) {
159 return new EphemeralConst<>(requireNonNull(name), supplier);
160 }
161
162 /**
163 * Create a new ephemeral constant with the given value {@code supplier}.
164 * For every newly created operation tree, a new constant value is chosen
165 * for this terminal operation. The value is than kept constant for this tree.
166 *
167 * @param supplier the value supplier
168 * @param <T> the constant type
169 * @return a new ephemeral constant
170 * @throws NullPointerException if the {@code supplier} is {@code null}
171 */
172 public static <T> EphemeralConst<T> of(final Supplier<T> supplier) {
173 return new EphemeralConst<>(null, supplier);
174 }
175
176
177 /* *************************************************************************
178 * Java object serialization
179 * ************************************************************************/
180
181 @Serial
182 private Object writeReplace() {
183 return new SerialProxy(SerialProxy.EPHEMERAL_CONST, this);
184 }
185
186 @Serial
187 private void readObject(final ObjectInputStream stream)
188 throws InvalidObjectException
189 {
190 throw new InvalidObjectException("Serialization proxy required.");
191 }
192
193 void write(final ObjectOutput out) throws IOException {
194 writeNullableString(name(), out);
195 out.writeObject(value());
196 out.writeObject(_supplier);
197 }
198
199 @SuppressWarnings({"unchecked", "rawtypes"})
200 static EphemeralConst read(final ObjectInput in)
201 throws IOException, ClassNotFoundException
202 {
203 final String name = readNullableString(in);
204 final Object value = in.readObject();
205 final Supplier supplier = (Supplier)in.readObject();
206
207 return new EphemeralConst(name, Lazy.ofValue(value), supplier);
208 }
209
210 }
|