001 /*
002 * Java Genetic Algorithm Library (jenetics-3.5.0).
003 * Copyright (c) 2007-2016 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.internal.util;
021
022 import static java.util.Objects.requireNonNull;
023
024 import java.io.Serializable;
025 import java.util.Objects;
026 import java.util.function.Supplier;
027
028 /**
029 * Class for lazy value initialization.
030 *
031 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
032 * @since 3.0
033 * @version 3.4
034 */
035 public final class Lazy<T> implements Supplier<T>, Serializable {
036 private static final long serialVersionUID = 1L;
037
038 private final Supplier<T> _supplier;
039
040 private T _value;
041 private volatile boolean _evaluated = false;
042
043 private Lazy(final Supplier<T> supplier) {
044 _supplier = requireNonNull(supplier);
045 }
046
047 @Override
048 public T get() {
049 return _evaluated ? _value : evaluate();
050 }
051
052 /**
053 * Return the evaluation state of the {@code Lazy} variable.
054 *
055 * @return {@code true} is the {@code Lazy} variable has been evaluated,
056 * {@code false} otherwise
057 */
058 public synchronized boolean isEvaluated() {
059 return _evaluated;
060 }
061
062 private synchronized T evaluate() {
063 if (!_evaluated) {
064 _value = _supplier.get();
065 _evaluated = true;
066 }
067
068 return _value;
069 }
070
071 @Override
072 public int hashCode() {
073 return Objects.hashCode(get());
074 }
075
076 @Override
077 public boolean equals(final Object obj) {
078 if (this == obj) return true;
079 if (!(obj instanceof Lazy<?>)) return false;
080
081 final Lazy<?> lazy = (Lazy<?>)obj;
082 return Objects.equals(get(), lazy.get());
083 }
084
085 @Override
086 public String toString() {
087 return Objects.toString(get());
088 }
089
090 /**
091 * Create a new lazy value initialization.
092 *
093 * @param supplier the lazy value supplier
094 * @param <T> the value type
095 * @return a new lazy value initialization
096 * @throws java.lang.NullPointerException if the given supplier is
097 * {@code null}
098 */
099 public static <T> Lazy<T> of(final Supplier<T> supplier) {
100 return new Lazy<>(supplier);
101 }
102
103 }
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