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
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7 * published by the Free Software Foundation. Oracle designates this
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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 *
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24 */
25 package java.util.stream;
26
27 import java.nio.charset.Charset;
28 import java.nio.file.Files;
29 import java.nio.file.Path;
30 import java.util.Arrays;
31 import java.util.Collection;
32 import java.util.IntSummaryStatistics;
33 import java.util.Objects;
34 import java.util.OptionalDouble;
35 import java.util.OptionalInt;
36 import java.util.PrimitiveIterator;
37 import java.util.Spliterator;
38 import java.util.Spliterators;
39 import java.util.concurrent.ConcurrentHashMap;
40 import java.util.function.BiConsumer;
41 import java.util.function.Function;
42 import java.util.function.IntBinaryOperator;
43 import java.util.function.IntConsumer;
44 import java.util.function.IntFunction;
45 import java.util.function.IntPredicate;
46 import java.util.function.IntSupplier;
47 import java.util.function.IntToDoubleFunction;
48 import java.util.function.IntToLongFunction;
49 import java.util.function.IntUnaryOperator;
50 import java.util.function.ObjIntConsumer;
51 import java.util.function.Supplier;
52
53 /**
54 * A sequence of elements supporting sequential and parallel aggregate
55 * operations. The following example illustrates an aggregate operation using
56 * {@link Stream} and {@link IntStream}:
57 *
58 * <pre>{@code
59 * int sum = widgets.stream()
60 * .filter(w -> w.getColor() == RED)
61 * .mapToInt(w -> w.getWeight())
62 * .sum();
63 * }</pre>
64 *
65 * In this example, {@code widgets} is a {@code Collection<Widget>}. We create
66 * a stream of {@code Widget} objects via {@link Collection#stream Collection.stream()},
67 * filter it to produce a stream containing only the red widgets, and then
68 * transform it into a stream of {@code int} values representing the weight of
69 * each red widget. Then this stream is summed to produce a total weight.
70 *
71 * <p>To perform a computation, stream
72 * <a href="package-summary.html#StreamOps">operations</a> are composed into a
73 * <em>stream pipeline</em>. A stream pipeline consists of a source (which
74 * might be an array, a collection, a generator function, an IO channel,
75 * etc), zero or more <em>intermediate operations</em> (which transform a
76 * stream into another stream, such as {@link IntStream#filter(IntPredicate)}), and a
77 * <em>terminal operation</em> (which produces a result or side-effect, such
78 * as {@link IntStream#sum()} or {@link IntStream#forEach(IntConsumer)}).
79 * Streams are lazy; computation on the source data is only performed when the
80 * terminal operation is initiated, and source elements are consumed only
81 * as needed.
82 *
83 * <p>Collections and streams, while bearing some superficial similarities,
84 * have different goals. Collections are primarily concerned with the efficient
85 * management of, and access to, their elements. By contrast, streams do not
86 * provide a means to directly access or manipulate their elements, and are
87 * instead concerned with declaratively describing their source and the
88 * computational operations which will be performed in aggregate on that source.
89 * However, if the provided stream operations do not offer the desired
90 * functionality, the {@link #iterator()} and {@link #spliterator()} operations
91 * can be used to perform a controlled traversal.
92 *
93 * <p>A stream pipeline, like the "widgets" example above, can be viewed as
94 * a <em>query</em> on the stream source. Unless the source was explicitly
95 * designed for concurrent modification (such as a {@link ConcurrentHashMap}),
96 * unpredictable or erroneous behavior may result from modifying the stream
97 * source while it is being queried.
98 *
99 * <p>Most stream operations accept parameters that describe user-specified
100 * behavior, such as the lambda expression {@code w -> w.getWeight()} passed to
101 * {@code mapToInt} in the example above. Such parameters are always instances
102 * of a <a href="../function/package-summary.html">functional interface</a> such
103 * as {@link java.util.function.Function}, and are often lambda expressions or
104 * method references. These parameters can never be null, should not modify the
105 * stream source, and should be
106 * <a href="package-summary.html#NonInterference">effectively stateless</a>
107 * (their result should not depend on any state that might change during
108 * execution of the stream pipeline.)
109 *
110 * <p>A stream should be operated on (invoking an intermediate or terminal stream
111 * operation) only once. This rules out, for example, "forked" streams, where
112 * the same source feeds two or more pipelines, or multiple traversals of the
113 * same stream. A stream implementation may throw {@link IllegalStateException}
114 * if it detects that the stream is being reused. However, since some stream
115 * operations may return their receiver rather than a new stream object, it may
116 * not be possible to detect reuse in all cases.
117 *
118 * <p>Streams have a {@link #close()} method and implement {@link AutoCloseable},
119 * but nearly all stream instances do not actually need to be closed after use.
120 * Generally, only streams whose source is an IO channel (such as those returned
121 * by {@link Files#lines(Path, Charset)}) will require closing. Most streams
122 * are backed by collections, arrays, or generating functions, which require no
123 * special resource management. (If a stream does require closing, it can be
124 * declared as a resource in a {@code try}-with-resources statement.)
125 *
126 * <p>Stream pipelines may execute either sequentially or in
127 * <a href="package-summary.html#Parallelism">parallel</a>. This
128 * execution mode is a property of the stream. Streams are created
129 * with an initial choice of sequential or parallel execution. (For example,
130 * {@link Collection#stream() Collection.stream()} creates a sequential stream,
131 * and {@link Collection#parallelStream() Collection.parallelStream()} creates
132 * a parallel one.) This choice of execution mode may be modified by the
133 * {@link #sequential()} or {@link #parallel()} methods, and may be queried with
134 * the {@link #isParallel()} method.
135 *
136 * @since 1.8
137 * @see <a href="package-summary.html">java.util.stream</a>
138 */
139 public interface IntStream extends BaseStream<Integer, IntStream> {
140
141 /**
142 * Returns a stream consisting of the elements of this stream that match
143 * the given predicate.
144 *
145 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
146 * operation</a>.
147 *
148 * @param predicate a <a href="package-summary.html#NonInterference">
149 * non-interfering, stateless</a> predicate to apply to
150 * each element to determine if it should be included
151 * @return the new stream
152 */
153 IntStream filter(IntPredicate predicate);
154
155 /**
156 * Returns a stream consisting of the results of applying the given
157 * function to the elements of this stream.
158 *
159 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
160 * operation</a>.
161 *
162 * @param mapper a <a href="package-summary.html#NonInterference">
163 * non-interfering, stateless</a> function to apply to each
164 * element
165 * @return the new stream
166 */
167 IntStream map(IntUnaryOperator mapper);
168
169 /**
170 * Returns an object-valued {@code Stream} consisting of the results of
171 * applying the given function to the elements of this stream.
172 *
173 * <p>This is an <a href="package-summary.html#StreamOps">
174 * intermediate operation</a>.
175 *
176 * @param <U> the element type of the new stream
177 * @param mapper a <a href="package-summary.html#NonInterference">
178 * non-interfering, stateless</a> function to apply to each
179 * element
180 * @return the new stream
181 */
182 <U> Stream<U> mapToObj(IntFunction<? extends U> mapper);
183
184 /**
185 * Returns a {@code LongStream} consisting of the results of applying the
186 * given function to the elements of this stream.
187 *
188 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
189 * operation</a>.
190 *
191 * @param mapper a <a href="package-summary.html#NonInterference">
192 * non-interfering, stateless</a> function to apply to each
193 * element
194 * @return the new stream
195 */
196 LongStream mapToLong(IntToLongFunction mapper);
197
198 /**
199 * Returns a {@code DoubleStream} consisting of the results of applying the
200 * given function to the elements of this stream.
201 *
202 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
203 * operation</a>.
204 *
205 * @param mapper a <a href="package-summary.html#NonInterference">
206 * non-interfering, stateless</a> function to apply to each
207 * element
208 * @return the new stream
209 */
210 DoubleStream mapToDouble(IntToDoubleFunction mapper);
211
212 /**
213 * Returns a stream consisting of the results of replacing each element of
214 * this stream with the contents of the stream produced by applying the
215 * provided mapping function to each element. (If the result of the mapping
216 * function is {@code null}, this is treated as if the result was an empty
217 * stream.)
218 *
219 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
220 * operation</a>.
221 *
222 * @param mapper a <a href="package-summary.html#NonInterference">
223 * non-interfering, stateless</a> function to apply to
224 * each element which produces an {@code IntStream} of new
225 * values
226 * @return the new stream
227 * @see Stream#flatMap(Function)
228 */
229 IntStream flatMap(IntFunction<? extends IntStream> mapper);
230
231 /**
232 * Returns a stream consisting of the distinct elements of this stream.
233 *
234 * <p>This is a <a href="package-summary.html#StreamOps">stateful
235 * intermediate operation</a>.
236 *
237 * @return the new stream
238 */
239 IntStream distinct();
240
241 /**
242 * Returns a stream consisting of the elements of this stream in sorted
243 * order.
244 *
245 * <p>This is a <a href="package-summary.html#StreamOps">stateful
246 * intermediate operation</a>.
247 *
248 * @return the new stream
249 */
250 IntStream sorted();
251
252 /**
253 * Returns a stream consisting of the elements of this stream, additionally
254 * performing the provided action on each element as elements are consumed
255 * from the resulting stream.
256 *
257 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
258 * operation</a>.
259 *
260 * <p>For parallel stream pipelines, the action may be called at
261 * whatever time and in whatever thread the element is made available by the
262 * upstream operation. If the action modifies shared state,
263 * it is responsible for providing the required synchronization.
264 *
265 * @apiNote This method exists mainly to support debugging, where you want
266 * to see the elements as they flow past a certain point in a pipeline:
267 * <pre>{@code
268 * list.stream()
269 * .filter(filteringFunction)
270 * .peek(e -> System.out.println("Filtered value: " + e));
271 * .map(mappingFunction)
272 * .peek(e -> System.out.println("Mapped value: " + e));
273 * .collect(Collectors.toIntSummaryStastistics());
274 * }</pre>
275 *
276 * @param action a <a href="package-summary.html#NonInterference">
277 * non-interfering</a> action to perform on the elements as
278 * they are consumed from the stream
279 * @return the new stream
280 */
281 IntStream peek(IntConsumer action);
282
283 /**
284 * Returns a stream consisting of the elements of this stream, truncated
285 * to be no longer than {@code maxSize} in length.
286 *
287 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
288 * stateful intermediate operation</a>.
289 *
290 * @apiNote
291 * While {@code limit()} is generally a cheap operation on sequential
292 * stream pipelines, it can be quite expensive on ordered parallel pipelines,
293 * especially for large values of {@code maxSize}, since {@code limit(n)}
294 * is constrained to return not just any <em>n</em> elements, but the
295 * <em>first n</em> elements in the encounter order. Using an unordered
296 * stream source (such as {@link #generate(IntSupplier)}) or removing the
297 * ordering constraint with {@link #unordered()} may result in significant
298 * speedups of {@code limit()} in parallel pipelines, if the semantics of
299 * your situation permit. If consistency with encounter order is required,
300 * and you are experiencing poor performance or memory utilization with
301 * {@code limit()} in parallel pipelines, switching to sequential execution
302 * with {@link #sequential()} may improve performance.
303 *
304 * @param maxSize the number of elements the stream should be limited to
305 * @return the new stream
306 * @throws IllegalArgumentException if {@code maxSize} is negative
307 */
308 IntStream limit(long maxSize);
309
310 /**
311 * Returns a stream consisting of the remaining elements of this stream
312 * after discarding the first {@code n} elements of the stream.
313 * If this stream contains fewer than {@code n} elements then an
314 * empty stream will be returned.
315 *
316 * <p>This is a <a href="package-summary.html#StreamOps">stateful
317 * intermediate operation</a>.
318 *
319 * @apiNote
320 * While {@code skip()} is generally a cheap operation on sequential
321 * stream pipelines, it can be quite expensive on ordered parallel pipelines,
322 * especially for large values of {@code n}, since {@code skip(n)}
323 * is constrained to skip not just any <em>n</em> elements, but the
324 * <em>first n</em> elements in the encounter order. Using an unordered
325 * stream source (such as {@link #generate(Supplier)}) or removing the
326 * ordering constraint with {@link #unordered()} may result in significant
327 * speedups of {@code skip()} in parallel pipelines, if the semantics of
328 * your situation permit. If consistency with encounter order is required,
329 * and you are experiencing poor performance or memory utilization with
330 * {@code skip()} in parallel pipelines, switching to sequential execution
331 * with {@link #sequential()} may improve performance.
332 *
333 * @param n the number of leading elements to skip
334 * @return the new stream
335 * @throws IllegalArgumentException if {@code n} is negative
336 */
337 IntStream skip(long n);
338
339 /**
340 * Performs an action for each element of this stream.
341 *
342 * <p>This is a <a href="package-summary.html#StreamOps">terminal
343 * operation</a>.
344 *
345 * <p>For parallel stream pipelines, this operation does <em>not</em>
346 * guarantee to respect the encounter order of the stream, as doing so
347 * would sacrifice the benefit of parallelism. For any given element, the
348 * action may be performed at whatever time and in whatever thread the
349 * library chooses. If the action accesses shared state, it is
350 * responsible for providing the required synchronization.
351 *
352 * @param action a <a href="package-summary.html#NonInterference">
353 * non-interfering</a> action to perform on the elements
354 */
355 void forEach(IntConsumer action);
356
357 /**
358 * Performs an action for each element of this stream, guaranteeing that
359 * each element is processed in encounter order for streams that have a
360 * defined encounter order.
361 *
362 * <p>This is a <a href="package-summary.html#StreamOps">terminal
363 * operation</a>.
364 *
365 * @param action a <a href="package-summary.html#NonInterference">
366 * non-interfering</a> action to perform on the elements
367 * @see #forEach(IntConsumer)
368 */
369 void forEachOrdered(IntConsumer action);
370
371 /**
372 * Returns an array containing the elements of this stream.
373 *
374 * <p>This is a <a href="package-summary.html#StreamOps">terminal
375 * operation</a>.
376 *
377 * @return an array containing the elements of this stream
378 */
379 int[] toArray();
380
381 /**
382 * Performs a <a href="package-summary.html#Reduction">reduction</a> on the
383 * elements of this stream, using the provided identity value and an
384 * <a href="package-summary.html#Associativity">associative</a>
385 * accumulation function, and returns the reduced value. This is equivalent
386 * to:
387 * <pre>{@code
388 * int result = identity;
389 * for (int element : this stream)
390 * result = accumulator.apply(result, element)
391 * return result;
392 * }</pre>
393 *
394 * but is not constrained to execute sequentially.
395 *
396 * <p>The {@code identity} value must be an identity for the accumulator
397 * function. This means that for all {@code x},
398 * {@code accumulator.apply(identity, x)} is equal to {@code x}.
399 * The {@code accumulator} function must be an
400 * <a href="package-summary.html#Associativity">associative</a> function.
401 *
402 * <p>This is a <a href="package-summary.html#StreamOps">terminal
403 * operation</a>.
404 *
405 * @apiNote Sum, min, max, and average are all special cases of reduction.
406 * Summing a stream of numbers can be expressed as:
407 *
408 * <pre>{@code
409 * int sum = integers.reduce(0, (a, b) -> a+b);
410 * }</pre>
411 *
412 * or more compactly:
413 *
414 * <pre>{@code
415 * int sum = integers.reduce(0, Integer::sum);
416 * }</pre>
417 *
418 * <p>While this may seem a more roundabout way to perform an aggregation
419 * compared to simply mutating a running total in a loop, reduction
420 * operations parallelize more gracefully, without needing additional
421 * synchronization and with greatly reduced risk of data races.
422 *
423 * @param identity the identity value for the accumulating function
424 * @param op an <a href="package-summary.html#Associativity">associative</a>
425 * <a href="package-summary.html#NonInterference">non-interfering,
426 * stateless</a> function for combining two values
427 * @return the result of the reduction
428 * @see #sum()
429 * @see #min()
430 * @see #max()
431 * @see #average()
432 */
433 int reduce(int identity, IntBinaryOperator op);
434
435 /**
436 * Performs a <a href="package-summary.html#Reduction">reduction</a> on the
437 * elements of this stream, using an
438 * <a href="package-summary.html#Associativity">associative</a> accumulation
439 * function, and returns an {@code OptionalInt} describing the reduced value,
440 * if any. This is equivalent to:
441 * <pre>{@code
442 * boolean foundAny = false;
443 * int result = null;
444 * for (int element : this stream) {
445 * if (!foundAny) {
446 * foundAny = true;
447 * result = element;
448 * }
449 * else
450 * result = accumulator.apply(result, element);
451 * }
452 * return foundAny ? OptionalInt.of(result) : OptionalInt.empty();
453 * }</pre>
454 *
455 * but is not constrained to execute sequentially.
456 *
457 * <p>The {@code accumulator} function must be an
458 * <a href="package-summary.html#Associativity">associative</a> function.
459 *
460 * <p>This is a <a href="package-summary.html#StreamOps">terminal
461 * operation</a>.
462 *
463 * @param op an <a href="package-summary.html#Associativity">associative</a>
464 * <a href="package-summary.html#NonInterference">non-interfering,
465 * stateless</a> function for combining two values
466 * @return the result of the reduction
467 * @see #reduce(int, IntBinaryOperator)
468 */
469 OptionalInt reduce(IntBinaryOperator op);
470
471 /**
472 * Performs a <a href="package-summary.html#MutableReduction">mutable
473 * reduction</a> operation on the elements of this stream. A mutable
474 * reduction is one in which the reduced value is a mutable result container,
475 * such as an {@code ArrayList}, and elements are incorporated by updating
476 * the state of the result rather than by replacing the result. This
477 * produces a result equivalent to:
478 * <pre>{@code
479 * R result = supplier.get();
480 * for (int element : this stream)
481 * accumulator.accept(result, element);
482 * return result;
483 * }</pre>
484 *
485 * <p>Like {@link #reduce(int, IntBinaryOperator)}, {@code collect} operations
486 * can be parallelized without requiring additional synchronization.
487 *
488 * <p>This is a <a href="package-summary.html#StreamOps">terminal
489 * operation</a>.
490 *
491 * @param <R> type of the result
492 * @param supplier a function that creates a new result container. For a
493 * parallel execution, this function may be called
494 * multiple times and must return a fresh value each time.
495 * @param accumulator an <a href="package-summary.html#Associativity">associative</a>
496 * <a href="package-summary.html#NonInterference">non-interfering,
497 * stateless</a> function for incorporating an additional
498 * element into a result
499 * @param combiner an <a href="package-summary.html#Associativity">associative</a>
500 * <a href="package-summary.html#NonInterference">non-interfering,
501 * stateless</a> function for combining two values, which
502 * must be compatible with the accumulator function
503 * @return the result of the reduction
504 * @see Stream#collect(Supplier, BiConsumer, BiConsumer)
505 */
506 <R> R collect(Supplier<R> supplier,
507 ObjIntConsumer<R> accumulator,
508 BiConsumer<R, R> combiner);
509
510 /**
511 * Returns the sum of elements in this stream. This is a special case
512 * of a <a href="package-summary.html#Reduction">reduction</a>
513 * and is equivalent to:
514 * <pre>{@code
515 * return reduce(0, Integer::sum);
516 * }</pre>
517 *
518 * <p>This is a <a href="package-summary.html#StreamOps">terminal
519 * operation</a>.
520 *
521 * @return the sum of elements in this stream
522 */
523 int sum();
524
525 /**
526 * Returns an {@code OptionalInt} describing the minimum element of this
527 * stream, or an empty optional if this stream is empty. This is a special
528 * case of a <a href="package-summary.html#Reduction">reduction</a>
529 * and is equivalent to:
530 * <pre>{@code
531 * return reduce(Integer::min);
532 * }</pre>
533 *
534 * <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>.
535 *
536 * @return an {@code OptionalInt} containing the minimum element of this
537 * stream, or an empty {@code OptionalInt} if the stream is empty
538 */
539 OptionalInt min();
540
541 /**
542 * Returns an {@code OptionalInt} describing the maximum element of this
543 * stream, or an empty optional if this stream is empty. This is a special
544 * case of a <a href="package-summary.html#Reduction">reduction</a>
545 * and is equivalent to:
546 * <pre>{@code
547 * return reduce(Integer::max);
548 * }</pre>
549 *
550 * <p>This is a <a href="package-summary.html#StreamOps">terminal
551 * operation</a>.
552 *
553 * @return an {@code OptionalInt} containing the maximum element of this
554 * stream, or an empty {@code OptionalInt} if the stream is empty
555 */
556 OptionalInt max();
557
558 /**
559 * Returns the count of elements in this stream. This is a special case of
560 * a <a href="package-summary.html#Reduction">reduction</a> and is
561 * equivalent to:
562 * <pre>{@code
563 * return mapToLong(e -> 1L).sum();
564 * }</pre>
565 *
566 * <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>.
567 *
568 * @return the count of elements in this stream
569 */
570 long count();
571
572 /**
573 * Returns an {@code OptionalDouble} describing the arithmetic mean of elements of
574 * this stream, or an empty optional if this stream is empty. This is a
575 * special case of a
576 * <a href="package-summary.html#Reduction">reduction</a>.
577 *
578 * <p>This is a <a href="package-summary.html#StreamOps">terminal
579 * operation</a>.
580 *
581 * @return an {@code OptionalDouble} containing the average element of this
582 * stream, or an empty optional if the stream is empty
583 */
584 OptionalDouble average();
585
586 /**
587 * Returns an {@code IntSummaryStatistics} describing various
588 * summary data about the elements of this stream. This is a special
589 * case of a <a href="package-summary.html#Reduction">reduction</a>.
590 *
591 * <p>This is a <a href="package-summary.html#StreamOps">terminal
592 * operation</a>.
593 *
594 * @return an {@code IntSummaryStatistics} describing various summary data
595 * about the elements of this stream
596 */
597 IntSummaryStatistics summaryStatistics();
598
599 /**
600 * Returns whether any elements of this stream match the provided
601 * predicate. May not evaluate the predicate on all elements if not
602 * necessary for determining the result.
603 *
604 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
605 * terminal operation</a>.
606 *
607 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
608 * stateless</a> predicate to apply to elements of this
609 * stream
610 * @return {@code true} if any elements of the stream match the provided
611 * predicate otherwise {@code false}
612 */
613 boolean anyMatch(IntPredicate predicate);
614
615 /**
616 * Returns whether all elements of this stream match the provided predicate.
617 * May not evaluate the predicate on all elements if not necessary for
618 * determining the result.
619 *
620 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
621 * terminal operation</a>.
622 *
623 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
624 * stateless</a> predicate to apply to elements of this
625 * stream
626 * @return {@code true} if all elements of the stream match the provided
627 * predicate otherwise {@code false}
628 */
629 boolean allMatch(IntPredicate predicate);
630
631 /**
632 * Returns whether no elements of this stream match the provided predicate.
633 * May not evaluate the predicate on all elements if not necessary for
634 * determining the result.
635 *
636 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
637 * terminal operation</a>.
638 *
639 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
640 * stateless</a> predicate to apply to elements of this
641 * stream
642 * @return {@code true} if no elements of the stream match the provided
643 * predicate otherwise {@code false}
644 */
645 boolean noneMatch(IntPredicate predicate);
646
647 /**
648 * Returns an {@link OptionalInt} describing the first element of this
649 * stream, or an empty {@code OptionalInt} if the stream is empty. If the
650 * stream has no encounter order, then any element may be returned.
651 *
652 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
653 * terminal operation</a>.
654 *
655 * @return an {@code OptionalInt} describing the first element of this stream,
656 * or an empty {@code OptionalInt} if the stream is empty
657 */
658 OptionalInt findFirst();
659
660 /**
661 * Returns an {@link OptionalInt} describing some element of the stream, or
662 * an empty {@code OptionalInt} if the stream is empty.
663 *
664 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
665 * terminal operation</a>.
666 *
667 * <p>The behavior of this operation is explicitly nondeterministic; it is
668 * free to select any element in the stream. This is to allow for maximal
669 * performance in parallel operations; the cost is that multiple invocations
670 * on the same source may not return the same result. (If a stable result
671 * is desired, use {@link #findFirst()} instead.)
672 *
673 * @return an {@code OptionalInt} describing some element of this stream, or
674 * an empty {@code OptionalInt} if the stream is empty
675 * @see #findFirst()
676 */
677 OptionalInt findAny();
678
679 /**
680 * Returns a {@code LongStream} consisting of the elements of this stream,
681 * converted to {@code long}.
682 *
683 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
684 * operation</a>.
685 *
686 * @return a {@code LongStream} consisting of the elements of this stream,
687 * converted to {@code long}
688 */
689 LongStream asLongStream();
690
691 /**
692 * Returns a {@code DoubleStream} consisting of the elements of this stream,
693 * converted to {@code double}.
694 *
695 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
696 * operation</a>.
697 *
698 * @return a {@code DoubleStream} consisting of the elements of this stream,
699 * converted to {@code double}
700 */
701 DoubleStream asDoubleStream();
702
703 /**
704 * Returns a {@code Stream} consisting of the elements of this stream,
705 * each boxed to an {@code Integer}.
706 *
707 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
708 * operation</a>.
709 *
710 * @return a {@code Stream} consistent of the elements of this stream,
711 * each boxed to an {@code Integer}
712 */
713 Stream<Integer> boxed();
714
715 @Override
716 IntStream sequential();
717
718 @Override
719 IntStream parallel();
720
721 @Override
722 PrimitiveIterator.OfInt iterator();
723
724 @Override
725 Spliterator.OfInt spliterator();
726
727 // Static factories
728
729 /**
730 * Returns a builder for an {@code IntStream}.
731 *
732 * @return a stream builder
733 */
734 public static Builder builder() {
735 return new Streams.IntStreamBuilderImpl();
736 }
737
738 /**
739 * Returns an empty sequential {@code IntStream}.
740 *
741 * @return an empty sequential stream
742 */
743 public static IntStream empty() {
744 return StreamSupport.intStream(Spliterators.emptyIntSpliterator(), false);
745 }
746
747 /**
748 * Returns a sequential {@code IntStream} containing a single element.
749 *
750 * @param t the single element
751 * @return a singleton sequential stream
752 */
753 public static IntStream of(int t) {
754 return StreamSupport.intStream(new Streams.IntStreamBuilderImpl(t), false);
755 }
756
757 /**
758 * Returns a sequential ordered stream whose elements are the specified values.
759 *
760 * @param values the elements of the new stream
761 * @return the new stream
762 */
763 public static IntStream of(int... values) {
764 return Arrays.stream(values);
765 }
766
767 /**
768 * Returns an infinite sequential ordered {@code IntStream} produced by iterative
769 * application of a function {@code f} to an initial element {@code seed},
770 * producing a {@code Stream} consisting of {@code seed}, {@code f(seed)},
771 * {@code f(f(seed))}, etc.
772 *
773 * <p>The first element (position {@code 0}) in the {@code IntStream} will be
774 * the provided {@code seed}. For {@code n > 0}, the element at position
775 * {@code n}, will be the result of applying the function {@code f} to the
776 * element at position {@code n - 1}.
777 *
778 * @param seed the initial element
779 * @param f a function to be applied to to the previous element to produce
780 * a new element
781 * @return A new sequential {@code IntStream}
782 */
783 public static IntStream iterate(final int seed, final IntUnaryOperator f) {
784 Objects.requireNonNull(f);
785 final PrimitiveIterator.OfInt iterator = new PrimitiveIterator.OfInt() {
786 int t = seed;
787
788 @Override
789 public boolean hasNext() {
790 return true;
791 }
792
793 @Override
794 public int nextInt() {
795 int v = t;
796 t = f.applyAsInt(t);
797 return v;
798 }
799 };
800 return StreamSupport.intStream(Spliterators.spliteratorUnknownSize(
801 iterator,
802 Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), false);
803 }
804
805 /**
806 * Returns a sequential stream where each element is generated by
807 * the provided {@code IntSupplier}. This is suitable for generating
808 * constant streams, streams of random elements, etc.
809 *
810 * @param s the {@code IntSupplier} for generated elements
811 * @return a new sequential {@code IntStream}
812 */
813 public static IntStream generate(IntSupplier s) {
814 Objects.requireNonNull(s);
815 return StreamSupport.intStream(
816 new StreamSpliterators.InfiniteSupplyingSpliterator.OfInt(Long.MAX_VALUE, s), false);
817 }
818
819 /**
820 * Returns a sequential ordered {@code IntStream} from {@code startInclusive}
821 * (inclusive) to {@code endExclusive} (exclusive) by an incremental step of
822 * {@code 1}.
823 *
824 * @apiNote
825 * <p>An equivalent sequence of increasing values can be produced
826 * sequentially using a {@code for} loop as follows:
827 * <pre>{@code
828 * for (int i = startInclusive; i < endExclusive ; i++) { ... }
829 * }</pre>
830 *
831 * @param startInclusive the (inclusive) initial value
832 * @param endExclusive the exclusive upper bound
833 * @return a sequential {@code IntStream} for the range of {@code int}
834 * elements
835 */
836 public static IntStream range(int startInclusive, int endExclusive) {
837 if (startInclusive >= endExclusive) {
838 return empty();
839 } else {
840 return StreamSupport.intStream(
841 new Streams.RangeIntSpliterator(startInclusive, endExclusive, false), false);
842 }
843 }
844
845 /**
846 * Returns a sequential ordered {@code IntStream} from {@code startInclusive}
847 * (inclusive) to {@code endInclusive} (inclusive) by an incremental step of
848 * {@code 1}.
849 *
850 * @apiNote
851 * <p>An equivalent sequence of increasing values can be produced
852 * sequentially using a {@code for} loop as follows:
853 * <pre>{@code
854 * for (int i = startInclusive; i <= endInclusive ; i++) { ... }
855 * }</pre>
856 *
857 * @param startInclusive the (inclusive) initial value
858 * @param endInclusive the inclusive upper bound
859 * @return a sequential {@code IntStream} for the range of {@code int}
860 * elements
861 */
862 public static IntStream rangeClosed(int startInclusive, int endInclusive) {
863 if (startInclusive > endInclusive) {
864 return empty();
865 } else {
866 return StreamSupport.intStream(
867 new Streams.RangeIntSpliterator(startInclusive, endInclusive, true), false);
868 }
869 }
870
871 /**
872 * Creates a lazily concatenated stream whose elements are all the
873 * elements of the first stream followed by all the elements of the
874 * second stream. The resulting stream is ordered if both
875 * of the input streams are ordered, and parallel if either of the input
876 * streams is parallel. When the resulting stream is closed, the close
877 * handlers for both input streams are invoked.
878 *
879 * @param a the first stream
880 * @param b the second stream
881 * @return the concatenation of the two input streams
882 */
883 public static IntStream concat(IntStream a, IntStream b) {
884 Objects.requireNonNull(a);
885 Objects.requireNonNull(b);
886
887 Spliterator.OfInt split = new Streams.ConcatSpliterator.OfInt(
888 a.spliterator(), b.spliterator());
889 IntStream stream = StreamSupport.intStream(split, a.isParallel() || b.isParallel());
890 return stream.onClose(Streams.composedClose(a, b));
891 }
892
893 /**
894 * A mutable builder for an {@code IntStream}.
895 *
896 * <p>A stream builder has a lifecycle, which starts in a building
897 * phase, during which elements can be added, and then transitions to a built
898 * phase, after which elements may not be added. The built phase
899 * begins when the {@link #build()} method is called, which creates an
900 * ordered stream whose elements are the elements that were added to the
901 * stream builder, in the order they were added.
902 *
903 * @see IntStream#builder()
904 * @since 1.8
905 */
906 public interface Builder extends IntConsumer {
907
908 /**
909 * Adds an element to the stream being built.
910 *
911 * @throws IllegalStateException if the builder has already transitioned
912 * to the built state
913 */
914 @Override
915 void accept(int t);
916
917 /**
918 * Adds an element to the stream being built.
919 *
920 * @implSpec
921 * The default implementation behaves as if:
922 * <pre>{@code
923 * accept(t)
924 * return this;
925 * }</pre>
926 *
927 * @param t the element to add
928 * @return {@code this} builder
929 * @throws IllegalStateException if the builder has already transitioned
930 * to the built state
931 */
932 default Builder add(int t) {
933 accept(t);
934 return this;
935 }
936
937 /**
938 * Builds the stream, transitioning this builder to the built state.
939 * An {@code IllegalStateException} is thrown if there are further
940 * attempts to operate on the builder after it has entered the built
941 * state.
942 *
943 * @return the built stream
944 * @throws IllegalStateException if the builder has already transitioned to
945 * the built state
946 */
947 IntStream build();
948 }
949 }