001 /*
002 * Java Genetic Algorithm Library (jenetics-1.6.0).
003 * Copyright (c) 2007-2014 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@gmx.at)
019 */
020 package org.jenetics.util;
021
022 import static org.jenetics.internal.util.object.eq;
023
024 import java.io.Serializable;
025 import java.util.Objects;
026
027 import javolution.lang.Reference;
028
029 import org.jenetics.internal.util.HashBuilder;
030
031 /**
032 * A final {@link Reference}. This class is used if you want to allow to set the
033 * value of a {@link Reference} only once. If you try to set the references
034 * value twice an {@link IllegalStateException} is thrown.
035 *
036 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
037 * @since 1.0
038 * @version 1.0 — <em>$Date: 2014-03-01 $</em>
039 */
040 public final class FinalReference<T> implements Reference<T>, Serializable {
041 private static final long serialVersionUID = 1L;
042
043 private T _value = null;
044 private boolean _initialized = false;
045
046 /**
047 * Create a new final reference.
048 */
049 public FinalReference() {
050 }
051
052 /**
053 * Create a new FinalReference with the given default value. The value of
054 * this reference can still be set, that means {@code isFinal() == false}.
055 *
056 * @param devault the default value of the reference.
057 */
058 public FinalReference(final T devault) {
059 _value = devault;
060 }
061
062 /**
063 * Test whether this {@link Reference} can be set without throwing an
064 * {@link IllegalStateException} or not.
065 *
066 * @return {@code true} if this {@link Reference} can't be set again,
067 * false otherwise.
068 */
069 public synchronized boolean isFinal() {
070 return _initialized;
071 }
072
073 /**
074 * Set the reference value. If you try to set the reference value twice an
075 * {@link IllegalStateException} is thrown.
076 *
077 * @throws IllegalStateException if you try to set the reference value twice.
078 */
079 @Override
080 public synchronized void set(final T value) {
081 if (_initialized) {
082 throw new IllegalStateException("Value is already initialized.");
083 }
084 _value = value;
085 _initialized = true;
086 }
087
088 @Override
089 public synchronized T get() {
090 return _value;
091 }
092
093 @Override
094 public int hashCode() {
095 return HashBuilder.of(getClass()).and(get()).value();
096 }
097
098 @Override
099 public boolean equals(final Object object) {
100 if (object == this) {
101 return true;
102 }
103 if (!(object instanceof FinalReference<?>)) {
104 return false;
105 }
106
107 final FinalReference<?> f = (FinalReference<?>)object;
108 return eq(get(), f.get());
109 }
110
111 @Override
112 public String toString() {
113 return Objects.toString(get());
114 }
115
116 }
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