001 /*
002 * Java Genetic Algorithm Library (jenetics-7.1.1).
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.util.Objects.requireNonNull;
023 import static io.jenetics.internal.util.SerialIO.readNullableString;
024 import static io.jenetics.internal.util.SerialIO.writeNullableString;
025
026 import java.io.IOException;
027 import java.io.InvalidObjectException;
028 import java.io.ObjectInput;
029 import java.io.ObjectInputStream;
030 import java.io.ObjectOutput;
031 import java.io.Serial;
032 import java.io.Serializable;
033 import java.util.Objects;
034
035 /**
036 * Represents an operation which always returns the same, constant, value. To
037 * improve readability, constants may have a name. If a name is given, this name
038 * is used when printing the program tree. The {@code Const} operation is a
039 * <em>terminal</em> operation.
040 *
041 * <pre>{@code
042 * final static Op<Double> PI = Const.of("π", Math.PI);
043 * final static Op<Double> ONE = Const.of(1.0);
044 * }</pre>
045 *
046 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
047 * @version 7.0
048 * @since 3.9
049 */
050 public final class Const<T> extends Val<T> implements Serializable {
051
052 @Serial
053 private static final long serialVersionUID = 2L;
054
055 private final T _const;
056
057 private Const(final String name, final T constant) {
058 super(name);
059 _const = constant;
060 }
061
062 @Override
063 public T value() {
064 return _const;
065 }
066
067 @Override
068 public String toString() {
069 return name() != null ? name() : Objects.toString(_const);
070 }
071
072 /**
073 * Return a new constant with the given name and value.
074 *
075 * @param name the constant name
076 * @param value the constant value
077 * @param <T> the constant type
078 * @return a new constant
079 * @throws NullPointerException if the given constant {@code name} is
080 * {@code null}
081 */
082 public static <T> Const<T> of(final String name, final T value) {
083 return new Const<>(requireNonNull(name), value);
084 }
085
086 /**
087 * Return a new constant with the given value.
088 *
089 * @param value the constant value
090 * @param <T> the constant type
091 * @return a new constant
092 */
093 public static <T> Const<T> of(final T value) {
094 return new Const<>(null, value);
095 }
096
097
098 /* *************************************************************************
099 * Java object serialization
100 * ************************************************************************/
101
102 @Serial
103 private Object writeReplace() {
104 return new SerialProxy(SerialProxy.CONST, this);
105 }
106
107 @Serial
108 private void readObject(final ObjectInputStream stream)
109 throws InvalidObjectException
110 {
111 throw new InvalidObjectException("Serialization proxy required.");
112 }
113
114 void write(final ObjectOutput out) throws IOException {
115 writeNullableString(name(), out);
116 out.writeObject(_const);
117 }
118
119 @SuppressWarnings({"unchecked", "rawtypes"})
120 static Object read(final ObjectInput in)
121 throws IOException, ClassNotFoundException
122 {
123 final String name = readNullableString(in);
124 final Object value = in.readObject();
125 return new Const(name, value);
126 }
127
128 }
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