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 java.lang.String.format;
023 import static java.util.Objects.requireNonNull;
024
025 import java.util.Random;
026
027 import org.jenetics.internal.math.probability;
028
029 /**
030 * Interface which delivers a stream of (positive) indexes ({@code int}s)s. The
031 * stream ends if {@link #next()} returns {@code -1}. Here some usage examples:
032 *
033 * [code]
034 * final IndexStream stream = ...;
035 * for (int index = stream.next(); index != -1; index = stream.next()) {
036 * System.out.println(index);
037 * }
038 * [/code]
039 * [code]
040 * final IndexStream stream = ...;
041 * int index = 0;
042 * while ((index = stream.next()) != -1) {
043 * System.out.println(index);
044 * }
045 * [/code]
046 *
047 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
048 * @since 1.0
049 * @version 1.1 — <em>$Date: 2014-02-15 $</em>
050 */
051 public abstract class IndexStream {
052
053 protected IndexStream() {
054 }
055
056 /**
057 * Return the next (positive inclusive zero) index, or -1 if the stream has
058 * reached its end.
059 *
060 * @return the next index, or -1 if the stream has reached its end.
061 */
062 public abstract int next();
063
064 /**
065 * Applies a {@code function} to all elements of this stream.
066 *
067 * @param function the function to apply to the elements.
068 * @throws NullPointerException if the given {@code function} is
069 * {@code null}.
070 */
071 <R> void forEach(final Function<? super Integer, ? extends R> function) {
072 requireNonNull(function, "Function");
073 for (int i = next(); i != -1; i = next()) {
074 function.apply(i);
075 }
076 }
077
078 /**
079 * Create a new random IndexIterator.
080 * @param n the maximal value (exclusively) the created index stream will
081 * return.
082 * @param probability the index selection probability.
083 * @throws IllegalArgumentException if {@code n == Integer.MAX_VALUE} or
084 * {@code n <= 0} or the given {@code probability} is not valid.
085 */
086 public static IndexStream Random(final int n, final double probability) {
087 return Random(n, probability, RandomRegistry.getRandom());
088 }
089
090 /**
091 * Create a new random IndexIterator. The elements returned by this stream
092 * are strictly increasing.
093 *
094 * @param n the maximal value (exclusively) the created index stream will
095 * return.
096 * @param p the index selection probability.
097 * @param random the random engine used for creating the random indexes.
098 * @throws IllegalArgumentException if {@code n == Integer.MAX_VALUE} or
099 * {@code n <= 0} or the given {@code probability} is not valid.
100 * @throws NullPointerException if the given {@code random} engine is
101 * {@code null}.
102 */
103 public static IndexStream Random(
104 final int n,
105 final double p,
106 final Random random
107 ) {
108 if (n == Integer.MAX_VALUE) {
109 throw new IllegalArgumentException(format(
110 "n must be smaller than Integer.MAX_VALUE."
111 ));
112 }
113 if (n <= 0) {
114 throw new IllegalArgumentException(format(
115 "n must be greater than zero: %d", n
116 ));
117 }
118
119 IndexStream stream = new RandomIndexStream(n, p, random);
120 if (Double.compare(p, 0.0) == 0) {
121 stream = new RandomIndexStreamP0();
122 } else if (Double.compare(p, 1.0) == 0) {
123 stream = new RandomIndexStreamP1(n);
124 }
125 return stream;
126 }
127
128 }
129
130 /**
131 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
132 * @since 1.4
133 * @version 1.5 — <em>$Date: 2014-02-15 $</em>
134 */
135 final class RandomIndexStream extends IndexStream {
136 private final int _n;
137 private final int _p;
138 private final Random _random;
139
140 private int _pos = -1;
141
142 RandomIndexStream(final int n, final double p, final Random random) {
143 _n = n;
144 _p = probability.toInt(p);
145 _random = requireNonNull(random, "Random object must not be null.");
146 }
147
148 @Override
149 public final int next() {
150 while (_pos < _n && _random.nextInt() >= _p) {
151 ++_pos;
152 }
153 ++_pos;
154
155 return _pos < _n ? _pos : -1;
156 }
157 }
158
159 /**
160 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
161 * @since 1.5
162 * @version 1.5 — <em>$Date: 2014-02-15 $</em>
163 */
164 final class RandomIndexStreamP0 extends IndexStream {
165 @Override public int next() {
166 return -1;
167 }
168 }
169
170 /**
171 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
172 * @since 1.5
173 * @version 1.5 — <em>$Date: 2014-02-15 $</em>
174 */
175 final class RandomIndexStreamP1 extends IndexStream {
176 private final int _n;
177 private int _pos = -1;
178
179 RandomIndexStreamP1(final int n) {
180 _n = n;
181 }
182
183 @Override public int next() {
184 ++_pos;
185 return _pos < _n ? _pos : -1;
186 }
187 }
|