1 /*
2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 package java.util.stream;
26
27 import java.util.Objects;
28 import java.util.Spliterator;
29 import java.util.function.Supplier;
30
31 /**
32 * Low-level utility methods for creating and manipulating streams.
33 *
34 * <p>This class is mostly for library writers presenting stream views
35 * of data structures; most static stream methods intended for end users are in
36 * the various {@code Stream} classes.
37 *
38 * @since 1.8
39 */
40 public final class StreamSupport {
41
42 // Suppresses default constructor, ensuring non-instantiability.
43 private StreamSupport() {}
44
45 /**
46 * Creates a new sequential or parallel {@code Stream} from a
47 * {@code Spliterator}.
48 *
49 * <p>The spliterator is only traversed, split, or queried for estimated
50 * size after the terminal operation of the stream pipeline commences.
51 *
52 * <p>It is strongly recommended the spliterator report a characteristic of
53 * {@code IMMUTABLE} or {@code CONCURRENT}, or be
54 * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise,
55 * {@link #stream(java.util.function.Supplier, int, boolean)} should be used
56 * to reduce the scope of potential interference with the source. See
57 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
58 * more details.
59 *
60 * @param <T> the type of stream elements
61 * @param spliterator a {@code Spliterator} describing the stream elements
62 * @param parallel if {@code true} then the returned stream is a parallel
63 * stream; if {@code false} the returned stream is a sequential
64 * stream.
65 * @return a new sequential or parallel {@code Stream}
66 */
67 public static <T> Stream<T> stream(Spliterator<T> spliterator, boolean parallel) {
68 Objects.requireNonNull(spliterator);
69 return new ReferencePipeline.Head<>(spliterator,
70 StreamOpFlag.fromCharacteristics(spliterator),
71 parallel);
72 }
73
74 /**
75 * Creates a new sequential or parallel {@code Stream} from a
76 * {@code Supplier} of {@code Spliterator}.
77 *
78 * <p>The {@link Supplier#get()} method will be invoked on the supplier no
79 * more than once, and only after the terminal operation of the stream pipeline
80 * commences.
81 *
82 * <p>For spliterators that report a characteristic of {@code IMMUTABLE}
83 * or {@code CONCURRENT}, or that are
84 * <a href="../Spliterator.html#binding">late-binding</a>, it is likely
85 * more efficient to use {@link #stream(java.util.Spliterator, boolean)}
86 * instead.
87 * <p>The use of a {@code Supplier} in this form provides a level of
88 * indirection that reduces the scope of potential interference with the
89 * source. Since the supplier is only invoked after the terminal operation
90 * commences, any modifications to the source up to the start of the
91 * terminal operation are reflected in the stream result. See
92 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
93 * more details.
94 *
95 * @param <T> the type of stream elements
96 * @param supplier a {@code Supplier} of a {@code Spliterator}
97 * @param characteristics Spliterator characteristics of the supplied
98 * {@code Spliterator}. The characteristics must be equal to
99 * {@code supplier.get().characteristics()}, otherwise undefined
100 * behavior may occur when terminal operation commences.
101 * @param parallel if {@code true} then the returned stream is a parallel
102 * stream; if {@code false} the returned stream is a sequential
103 * stream.
104 * @return a new sequential or parallel {@code Stream}
105 * @see #stream(java.util.Spliterator, boolean)
106 */
107 public static <T> Stream<T> stream(Supplier<? extends Spliterator<T>> supplier,
108 int characteristics,
109 boolean parallel) {
110 Objects.requireNonNull(supplier);
111 return new ReferencePipeline.Head<>(supplier,
112 StreamOpFlag.fromCharacteristics(characteristics),
113 parallel);
114 }
115
116 /**
117 * Creates a new sequential or parallel {@code IntStream} from a
118 * {@code Spliterator.OfInt}.
119 *
120 * <p>The spliterator is only traversed, split, or queried for estimated size
121 * after the terminal operation of the stream pipeline commences.
122 *
123 * <p>It is strongly recommended the spliterator report a characteristic of
124 * {@code IMMUTABLE} or {@code CONCURRENT}, or be
125 * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise,
126 * {@link #intStream(java.util.function.Supplier, int, boolean)} should be
127 * used to reduce the scope of potential interference with the source. See
128 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
129 * more details.
130 *
131 * @param spliterator a {@code Spliterator.OfInt} describing the stream elements
132 * @param parallel if {@code true} then the returned stream is a parallel
133 * stream; if {@code false} the returned stream is a sequential
134 * stream.
135 * @return a new sequential or parallel {@code IntStream}
136 */
137 public static IntStream intStream(Spliterator.OfInt spliterator, boolean parallel) {
138 return new IntPipeline.Head<>(spliterator,
139 StreamOpFlag.fromCharacteristics(spliterator),
140 parallel);
141 }
142
143 /**
144 * Creates a new sequential or parallel {@code IntStream} from a
145 * {@code Supplier} of {@code Spliterator.OfInt}.
146 *
147 * <p>The {@link Supplier#get()} method will be invoked on the supplier no
148 * more than once, and only after the terminal operation of the stream pipeline
149 * commences.
150 *
151 * <p>For spliterators that report a characteristic of {@code IMMUTABLE}
152 * or {@code CONCURRENT}, or that are
153 * <a href="../Spliterator.html#binding">late-binding</a>, it is likely
154 * more efficient to use {@link #intStream(java.util.Spliterator.OfInt, boolean)}
155 * instead.
156 * <p>The use of a {@code Supplier} in this form provides a level of
157 * indirection that reduces the scope of potential interference with the
158 * source. Since the supplier is only invoked after the terminal operation
159 * commences, any modifications to the source up to the start of the
160 * terminal operation are reflected in the stream result. See
161 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
162 * more details.
163 *
164 * @param supplier a {@code Supplier} of a {@code Spliterator.OfInt}
165 * @param characteristics Spliterator characteristics of the supplied
166 * {@code Spliterator.OfInt}. The characteristics must be equal to
167 * {@code supplier.get().characteristics()}, otherwise undefined
168 * behavior may occur when terminal operation commences.
169 * @param parallel if {@code true} then the returned stream is a parallel
170 * stream; if {@code false} the returned stream is a sequential
171 * stream.
172 * @return a new sequential or parallel {@code IntStream}
173 * @see #intStream(java.util.Spliterator.OfInt, boolean)
174 */
175 public static IntStream intStream(Supplier<? extends Spliterator.OfInt> supplier,
176 int characteristics,
177 boolean parallel) {
178 return new IntPipeline.Head<>(supplier,
179 StreamOpFlag.fromCharacteristics(characteristics),
180 parallel);
181 }
182
183 /**
184 * Creates a new sequential or parallel {@code LongStream} from a
185 * {@code Spliterator.OfLong}.
186 *
187 * <p>The spliterator is only traversed, split, or queried for estimated
188 * size after the terminal operation of the stream pipeline commences.
189 *
190 * <p>It is strongly recommended the spliterator report a characteristic of
191 * {@code IMMUTABLE} or {@code CONCURRENT}, or be
192 * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise,
193 * {@link #longStream(java.util.function.Supplier, int, boolean)} should be
194 * used to reduce the scope of potential interference with the source. See
195 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
196 * more details.
197 *
198 * @param spliterator a {@code Spliterator.OfLong} describing the stream elements
199 * @param parallel if {@code true} then the returned stream is a parallel
200 * stream; if {@code false} the returned stream is a sequential
201 * stream.
202 * @return a new sequential or parallel {@code LongStream}
203 */
204 public static LongStream longStream(Spliterator.OfLong spliterator,
205 boolean parallel) {
206 return new LongPipeline.Head<>(spliterator,
207 StreamOpFlag.fromCharacteristics(spliterator),
208 parallel);
209 }
210
211 /**
212 * Creates a new sequential or parallel {@code LongStream} from a
213 * {@code Supplier} of {@code Spliterator.OfLong}.
214 *
215 * <p>The {@link Supplier#get()} method will be invoked on the supplier no
216 * more than once, and only after the terminal operation of the stream pipeline
217 * commences.
218 *
219 * <p>For spliterators that report a characteristic of {@code IMMUTABLE}
220 * or {@code CONCURRENT}, or that are
221 * <a href="../Spliterator.html#binding">late-binding</a>, it is likely
222 * more efficient to use {@link #longStream(java.util.Spliterator.OfLong, boolean)}
223 * instead.
224 * <p>The use of a {@code Supplier} in this form provides a level of
225 * indirection that reduces the scope of potential interference with the
226 * source. Since the supplier is only invoked after the terminal operation
227 * commences, any modifications to the source up to the start of the
228 * terminal operation are reflected in the stream result. See
229 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
230 * more details.
231 *
232 * @param supplier a {@code Supplier} of a {@code Spliterator.OfLong}
233 * @param characteristics Spliterator characteristics of the supplied
234 * {@code Spliterator.OfLong}. The characteristics must be equal to
235 * {@code supplier.get().characteristics()}, otherwise undefined
236 * behavior may occur when terminal operation commences.
237 * @param parallel if {@code true} then the returned stream is a parallel
238 * stream; if {@code false} the returned stream is a sequential
239 * stream.
240 * @return a new sequential or parallel {@code LongStream}
241 * @see #longStream(java.util.Spliterator.OfLong, boolean)
242 */
243 public static LongStream longStream(Supplier<? extends Spliterator.OfLong> supplier,
244 int characteristics,
245 boolean parallel) {
246 return new LongPipeline.Head<>(supplier,
247 StreamOpFlag.fromCharacteristics(characteristics),
248 parallel);
249 }
250
251 /**
252 * Creates a new sequential or parallel {@code DoubleStream} from a
253 * {@code Spliterator.OfDouble}.
254 *
255 * <p>The spliterator is only traversed, split, or queried for estimated size
256 * after the terminal operation of the stream pipeline commences.
257 *
258 * <p>It is strongly recommended the spliterator report a characteristic of
259 * {@code IMMUTABLE} or {@code CONCURRENT}, or be
260 * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise,
261 * {@link #doubleStream(java.util.function.Supplier, int, boolean)} should
262 * be used to reduce the scope of potential interference with the source. See
263 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
264 * more details.
265 *
266 * @param spliterator A {@code Spliterator.OfDouble} describing the stream elements
267 * @param parallel if {@code true} then the returned stream is a parallel
268 * stream; if {@code false} the returned stream is a sequential
269 * stream.
270 * @return a new sequential or parallel {@code DoubleStream}
271 */
272 public static DoubleStream doubleStream(Spliterator.OfDouble spliterator,
273 boolean parallel) {
274 return new DoublePipeline.Head<>(spliterator,
275 StreamOpFlag.fromCharacteristics(spliterator),
276 parallel);
277 }
278
279 /**
280 * Creates a new sequential or parallel {@code DoubleStream} from a
281 * {@code Supplier} of {@code Spliterator.OfDouble}.
282 *
283 * <p>The {@link Supplier#get()} method will be invoked on the supplier no
284 * more than once, and only after the terminal operation of the stream pipeline
285 * commences.
286 *
287 * <p>For spliterators that report a characteristic of {@code IMMUTABLE}
288 * or {@code CONCURRENT}, or that are
289 * <a href="../Spliterator.html#binding">late-binding</a>, it is likely
290 * more efficient to use {@link #doubleStream(java.util.Spliterator.OfDouble, boolean)}
291 * instead.
292 * <p>The use of a {@code Supplier} in this form provides a level of
293 * indirection that reduces the scope of potential interference with the
294 * source. Since the supplier is only invoked after the terminal operation
295 * commences, any modifications to the source up to the start of the
296 * terminal operation are reflected in the stream result. See
297 * <a href="package-summary.html#NonInterference">Non-Interference</a> for
298 * more details.
299 *
300 * @param supplier A {@code Supplier} of a {@code Spliterator.OfDouble}
301 * @param characteristics Spliterator characteristics of the supplied
302 * {@code Spliterator.OfDouble}. The characteristics must be equal to
303 * {@code supplier.get().characteristics()}, otherwise undefined
304 * behavior may occur when terminal operation commences.
305 * @param parallel if {@code true} then the returned stream is a parallel
306 * stream; if {@code false} the returned stream is a sequential
307 * stream.
308 * @return a new sequential or parallel {@code DoubleStream}
309 * @see #doubleStream(java.util.Spliterator.OfDouble, boolean)
310 */
311 public static DoubleStream doubleStream(Supplier<? extends Spliterator.OfDouble> supplier,
312 int characteristics,
313 boolean parallel) {
314 return new DoublePipeline.Head<>(supplier,
315 StreamOpFlag.fromCharacteristics(characteristics),
316 parallel);
317 }
318 }