001 /*
002 * Java Genetic Algorithm Library (jenetics-6.1.0).
003 * Copyright (c) 2007-2020 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.Serializable;
032 import java.util.Objects;
033
034 /**
035 * Represents an operation which always returns the same, constant, value. To
036 * improve readability, constants may have a name. If a name is given, this name
037 * is used when printing the program tree. The {@code Const} operation is a
038 * <em>terminal</em> operation.
039 *
040 * <pre>{@code
041 * final static Op<Double> PI = Const.of("π", Math.PI);
042 * final static Op<Double> ONE = Const.of(1.0);
043 * }</pre>
044 *
045 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
046 * @version 5.0
047 * @since 3.9
048 */
049 public final class Const<T> extends Val<T> implements Serializable {
050
051 private static final long serialVersionUID = 2L;
052
053 private final T _const;
054
055 private Const(final String name, final T constant) {
056 super(name);
057 _const = constant;
058 }
059
060 @Override
061 public T value() {
062 return _const;
063 }
064
065 @Override
066 public String toString() {
067 return name() != null ? name() : Objects.toString(_const);
068 }
069
070 /**
071 * Return a new constant with the given name and value.
072 *
073 * @param name the constant name
074 * @param value the constant value
075 * @param <T> the constant type
076 * @return a new constant
077 * @throws NullPointerException if the given constant {@code name} is
078 * {@code null}
079 */
080 public static <T> Const<T> of(final String name, final T value) {
081 return new Const<>(requireNonNull(name), value);
082 }
083
084 /**
085 * Return a new constant with the given value.
086 *
087 * @param value the constant value
088 * @param <T> the constant type
089 * @return a new constant
090 */
091 public static <T> Const<T> of(final T value) {
092 return new Const<>(null, value);
093 }
094
095
096 /* *************************************************************************
097 * Java object serialization
098 * ************************************************************************/
099
100 private Object writeReplace() {
101 return new Serial(Serial.CONST, this);
102 }
103
104 private void readObject(final ObjectInputStream stream)
105 throws InvalidObjectException
106 {
107 throw new InvalidObjectException("Serialization proxy required.");
108 }
109
110 void write(final ObjectOutput out) throws IOException {
111 writeNullableString(name(), out);
112 out.writeObject(_const);
113 }
114
115 @SuppressWarnings({"unchecked", "rawtypes"})
116 static Object read(final ObjectInput in)
117 throws IOException, ClassNotFoundException
118 {
119 final String name = readNullableString(in);
120 final Object value = in.readObject();
121 return new Const(name, value);
122 }
123
124 }
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