1 /*
2 * Copyright (c) 2012, 2014, 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
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23 * questions.
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.DoubleSummaryStatistics;
33 import java.util.Objects;
34 import java.util.OptionalDouble;
35 import java.util.PrimitiveIterator;
36 import java.util.Spliterator;
37 import java.util.Spliterators;
38 import java.util.concurrent.ConcurrentHashMap;
39 import java.util.function.BiConsumer;
40 import java.util.function.DoubleBinaryOperator;
41 import java.util.function.DoubleConsumer;
42 import java.util.function.DoubleFunction;
43 import java.util.function.DoublePredicate;
44 import java.util.function.DoubleSupplier;
45 import java.util.function.DoubleToIntFunction;
46 import java.util.function.DoubleToLongFunction;
47 import java.util.function.DoubleUnaryOperator;
48 import java.util.function.Function;
49 import java.util.function.ObjDoubleConsumer;
50 import java.util.function.Supplier;
51
52 /**
53 * A sequence of primitive double-valued elements supporting sequential and parallel
54 * aggregate operations. This is the {@code double} primitive specialization of
55 * {@link Stream}.
56 *
57 * <p>The following example illustrates an aggregate operation using
58 * {@link Stream} and {@link DoubleStream}, computing the sum of the weights of the
59 * red widgets:
60 *
61 * <pre>{@code
62 * double sum = widgets.stream()
63 * .filter(w -> w.getColor() == RED)
64 * .mapToDouble(w -> w.getWeight())
65 * .sum();
66 * }</pre>
67 *
68 * See the class documentation for {@link Stream} and the package documentation
69 * for <a href="package-summary.html">java.util.stream</a> for additional
70 * specification of streams, stream operations, stream pipelines, and
71 * parallelism.
72 *
73 * @since 1.8
74 * @see Stream
75 * @see <a href="package-summary.html">java.util.stream</a>
76 */
77 public interface DoubleStream extends BaseStream<Double, DoubleStream> {
78
79 /**
80 * Returns a stream consisting of the elements of this stream that match
81 * the given predicate.
82 *
83 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
84 * operation</a>.
85 *
86 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
87 * <a href="package-summary.html#Statelessness">stateless</a>
88 * predicate to apply to each element to determine if it
89 * should be included
90 * @return the new stream
91 */
92 DoubleStream filter(DoublePredicate predicate);
93
94 /**
95 * Returns a stream consisting of the results of applying the given
96 * function to the elements of this stream.
97 *
98 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
99 * operation</a>.
100 *
101 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
102 * <a href="package-summary.html#Statelessness">stateless</a>
103 * function to apply to each element
104 * @return the new stream
105 */
106 DoubleStream map(DoubleUnaryOperator mapper);
107
108 /**
109 * Returns an object-valued {@code Stream} consisting of the results of
110 * applying the given function to the elements of this stream.
111 *
112 * <p>This is an <a href="package-summary.html#StreamOps">
113 * intermediate operation</a>.
114 *
115 * @param <U> the element type of the new stream
116 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
117 * <a href="package-summary.html#Statelessness">stateless</a>
118 * function to apply to each element
119 * @return the new stream
120 */
121 <U> Stream<U> mapToObj(DoubleFunction<? extends U> mapper);
122
123 /**
124 * Returns an {@code IntStream} consisting of the results of applying the
125 * given function to the elements of this stream.
126 *
127 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
128 * operation</a>.
129 *
130 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
131 * <a href="package-summary.html#Statelessness">stateless</a>
132 * function to apply to each element
133 * @return the new stream
134 */
135 IntStream mapToInt(DoubleToIntFunction mapper);
136
137 /**
138 * Returns a {@code LongStream} consisting of the results of applying the
139 * given function to the elements of this stream.
140 *
141 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
142 * operation</a>.
143 *
144 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
145 * <a href="package-summary.html#Statelessness">stateless</a>
146 * function to apply to each element
147 * @return the new stream
148 */
149 LongStream mapToLong(DoubleToLongFunction mapper);
150
151 /**
152 * Returns a stream consisting of the results of replacing each element of
153 * this stream with the contents of a mapped stream produced by applying
154 * the provided mapping function to each element. Each mapped stream is
155 * {@link java.util.stream.BaseStream#close() closed} after its contents
156 * have been placed into this stream. (If a mapped stream is {@code null}
157 * an empty stream is used, instead.)
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">non-interfering</a>,
163 * <a href="package-summary.html#Statelessness">stateless</a>
164 * function to apply to each element which produces a
165 * {@code DoubleStream} of new values
166 * @return the new stream
167 * @see Stream#flatMap(Function)
168 */
169 DoubleStream flatMap(DoubleFunction<? extends DoubleStream> mapper);
170
171 /**
172 * Returns a stream consisting of the distinct elements of this stream. The
173 * elements are compared for equality according to
174 * {@link java.lang.Double#compare(double, double)}.
175 *
176 * <p>This is a <a href="package-summary.html#StreamOps">stateful
177 * intermediate operation</a>.
178 *
179 * @return the result stream
180 */
181 DoubleStream distinct();
182
183 /**
184 * Returns a stream consisting of the elements of this stream in sorted
185 * order. The elements are compared for equality according to
186 * {@link java.lang.Double#compare(double, double)}.
187 *
188 * <p>This is a <a href="package-summary.html#StreamOps">stateful
189 * intermediate operation</a>.
190 *
191 * @return the result stream
192 */
193 DoubleStream sorted();
194
195 /**
196 * Returns a stream consisting of the elements of this stream, additionally
197 * performing the provided action on each element as elements are consumed
198 * from the resulting stream.
199 *
200 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
201 * operation</a>.
202 *
203 * <p>For parallel stream pipelines, the action may be called at
204 * whatever time and in whatever thread the element is made available by the
205 * upstream operation. If the action modifies shared state,
206 * it is responsible for providing the required synchronization.
207 *
208 * @apiNote This method exists mainly to support debugging, where you want
209 * to see the elements as they flow past a certain point in a pipeline:
210 * <pre>{@code
211 * DoubleStream.of(1, 2, 3, 4)
212 * .filter(e -> e > 2)
213 * .peek(e -> System.out.println("Filtered value: " + e))
214 * .map(e -> e * e)
215 * .peek(e -> System.out.println("Mapped value: " + e))
216 * .sum();
217 * }</pre>
218 *
219 * @param action a <a href="package-summary.html#NonInterference">
220 * non-interfering</a> action to perform on the elements as
221 * they are consumed from the stream
222 * @return the new stream
223 */
224 DoubleStream peek(DoubleConsumer action);
225
226 /**
227 * Returns a stream consisting of the elements of this stream, truncated
228 * to be no longer than {@code maxSize} in length.
229 *
230 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
231 * stateful intermediate operation</a>.
232 *
233 * @apiNote
234 * While {@code limit()} is generally a cheap operation on sequential
235 * stream pipelines, it can be quite expensive on ordered parallel pipelines,
236 * especially for large values of {@code maxSize}, since {@code limit(n)}
237 * is constrained to return not just any <em>n</em> elements, but the
238 * <em>first n</em> elements in the encounter order. Using an unordered
239 * stream source (such as {@link #generate(DoubleSupplier)}) or removing the
240 * ordering constraint with {@link #unordered()} may result in significant
241 * speedups of {@code limit()} in parallel pipelines, if the semantics of
242 * your situation permit. If consistency with encounter order is required,
243 * and you are experiencing poor performance or memory utilization with
244 * {@code limit()} in parallel pipelines, switching to sequential execution
245 * with {@link #sequential()} may improve performance.
246 *
247 * @param maxSize the number of elements the stream should be limited to
248 * @return the new stream
249 * @throws IllegalArgumentException if {@code maxSize} is negative
250 */
251 DoubleStream limit(long maxSize);
252
253 /**
254 * Returns a stream consisting of the remaining elements of this stream
255 * after discarding the first {@code n} elements of the stream.
256 * If this stream contains fewer than {@code n} elements then an
257 * empty stream will be returned.
258 *
259 * <p>This is a <a href="package-summary.html#StreamOps">stateful
260 * intermediate operation</a>.
261 *
262 * @apiNote
263 * While {@code skip()} is generally a cheap operation on sequential
264 * stream pipelines, it can be quite expensive on ordered parallel pipelines,
265 * especially for large values of {@code n}, since {@code skip(n)}
266 * is constrained to skip not just any <em>n</em> elements, but the
267 * <em>first n</em> elements in the encounter order. Using an unordered
268 * stream source (such as {@link #generate(DoubleSupplier)}) or removing the
269 * ordering constraint with {@link #unordered()} may result in significant
270 * speedups of {@code skip()} in parallel pipelines, if the semantics of
271 * your situation permit. If consistency with encounter order is required,
272 * and you are experiencing poor performance or memory utilization with
273 * {@code skip()} in parallel pipelines, switching to sequential execution
274 * with {@link #sequential()} may improve performance.
275 *
276 * @param n the number of leading elements to skip
277 * @return the new stream
278 * @throws IllegalArgumentException if {@code n} is negative
279 */
280 DoubleStream skip(long n);
281
282 /**
283 * Performs an action for each element of this stream.
284 *
285 * <p>This is a <a href="package-summary.html#StreamOps">terminal
286 * operation</a>.
287 *
288 * <p>For parallel stream pipelines, this operation does <em>not</em>
289 * guarantee to respect the encounter order of the stream, as doing so
290 * would sacrifice the benefit of parallelism. For any given element, the
291 * action may be performed at whatever time and in whatever thread the
292 * library chooses. If the action accesses shared state, it is
293 * responsible for providing the required synchronization.
294 *
295 * @param action a <a href="package-summary.html#NonInterference">
296 * non-interfering</a> action to perform on the elements
297 */
298 void forEach(DoubleConsumer action);
299
300 /**
301 * Performs an action for each element of this stream, guaranteeing that
302 * each element is processed in encounter order for streams that have a
303 * defined encounter order.
304 *
305 * <p>This is a <a href="package-summary.html#StreamOps">terminal
306 * operation</a>.
307 *
308 * @param action a <a href="package-summary.html#NonInterference">
309 * non-interfering</a> action to perform on the elements
310 * @see #forEach(DoubleConsumer)
311 */
312 void forEachOrdered(DoubleConsumer action);
313
314 /**
315 * Returns an array containing the elements of this stream.
316 *
317 * <p>This is a <a href="package-summary.html#StreamOps">terminal
318 * operation</a>.
319 *
320 * @return an array containing the elements of this stream
321 */
322 double[] toArray();
323
324 /**
325 * Performs a <a href="package-summary.html#Reduction">reduction</a> on the
326 * elements of this stream, using the provided identity value and an
327 * <a href="package-summary.html#Associativity">associative</a>
328 * accumulation function, and returns the reduced value. This is equivalent
329 * to:
330 * <pre>{@code
331 * double result = identity;
332 * for (double element : this stream)
333 * result = accumulator.applyAsDouble(result, element)
334 * return result;
335 * }</pre>
336 *
337 * but is not constrained to execute sequentially.
338 *
339 * <p>The {@code identity} value must be an identity for the accumulator
340 * function. This means that for all {@code x},
341 * {@code accumulator.apply(identity, x)} is equal to {@code x}.
342 * The {@code accumulator} function must be an
343 * <a href="package-summary.html#Associativity">associative</a> function.
344 *
345 * <p>This is a <a href="package-summary.html#StreamOps">terminal
346 * operation</a>.
347 *
348 * @apiNote Sum, min, max, and average are all special cases of reduction.
349 * Summing a stream of numbers can be expressed as:
350
351 * <pre>{@code
352 * double sum = numbers.reduce(0, (a, b) -> a+b);
353 * }</pre>
354 *
355 * or more compactly:
356 *
357 * <pre>{@code
358 * double sum = numbers.reduce(0, Double::sum);
359 * }</pre>
360 *
361 * <p>While this may seem a more roundabout way to perform an aggregation
362 * compared to simply mutating a running total in a loop, reduction
363 * operations parallelize more gracefully, without needing additional
364 * synchronization and with greatly reduced risk of data races.
365 *
366 * @param identity the identity value for the accumulating function
367 * @param op an <a href="package-summary.html#Associativity">associative</a>,
368 * <a href="package-summary.html#NonInterference">non-interfering</a>,
369 * <a href="package-summary.html#Statelessness">stateless</a>
370 * function for combining two values
371 * @return the result of the reduction
372 * @see #sum()
373 * @see #min()
374 * @see #max()
375 * @see #average()
376 */
377 double reduce(double identity, DoubleBinaryOperator op);
378
379 /**
380 * Performs a <a href="package-summary.html#Reduction">reduction</a> on the
381 * elements of this stream, using an
382 * <a href="package-summary.html#Associativity">associative</a> accumulation
383 * function, and returns an {@code OptionalDouble} describing the reduced
384 * value, if any. This is equivalent to:
385 * <pre>{@code
386 * boolean foundAny = false;
387 * double result = null;
388 * for (double element : this stream) {
389 * if (!foundAny) {
390 * foundAny = true;
391 * result = element;
392 * }
393 * else
394 * result = accumulator.applyAsDouble(result, element);
395 * }
396 * return foundAny ? OptionalDouble.of(result) : OptionalDouble.empty();
397 * }</pre>
398 *
399 * but is not constrained to execute sequentially.
400 *
401 * <p>The {@code accumulator} function must be an
402 * <a href="package-summary.html#Associativity">associative</a> function.
403 *
404 * <p>This is a <a href="package-summary.html#StreamOps">terminal
405 * operation</a>.
406 *
407 * @param op an <a href="package-summary.html#Associativity">associative</a>,
408 * <a href="package-summary.html#NonInterference">non-interfering</a>,
409 * <a href="package-summary.html#Statelessness">stateless</a>
410 * function for combining two values
411 * @return the result of the reduction
412 * @see #reduce(double, DoubleBinaryOperator)
413 */
414 OptionalDouble reduce(DoubleBinaryOperator op);
415
416 /**
417 * Performs a <a href="package-summary.html#MutableReduction">mutable
418 * reduction</a> operation on the elements of this stream. A mutable
419 * reduction is one in which the reduced value is a mutable result container,
420 * such as an {@code ArrayList}, and elements are incorporated by updating
421 * the state of the result rather than by replacing the result. This
422 * produces a result equivalent to:
423 * <pre>{@code
424 * R result = supplier.get();
425 * for (double element : this stream)
426 * accumulator.accept(result, element);
427 * return result;
428 * }</pre>
429 *
430 * <p>Like {@link #reduce(double, DoubleBinaryOperator)}, {@code collect}
431 * operations can be parallelized without requiring additional
432 * synchronization.
433 *
434 * <p>This is a <a href="package-summary.html#StreamOps">terminal
435 * operation</a>.
436 *
437 * @param <R> type of the result
438 * @param supplier a function that creates a new result container. For a
439 * parallel execution, this function may be called
440 * multiple times and must return a fresh value each time.
441 * @param accumulator an <a href="package-summary.html#Associativity">associative</a>,
442 * <a href="package-summary.html#NonInterference">non-interfering</a>,
443 * <a href="package-summary.html#Statelessness">stateless</a>
444 * function for incorporating an additional element into a result
445 * @param combiner an <a href="package-summary.html#Associativity">associative</a>,
446 * <a href="package-summary.html#NonInterference">non-interfering</a>,
447 * <a href="package-summary.html#Statelessness">stateless</a>
448 * function for combining two values, which must be
449 * compatible with the accumulator function
450 * @return the result of the reduction
451 * @see Stream#collect(Supplier, BiConsumer, BiConsumer)
452 */
453 <R> R collect(Supplier<R> supplier,
454 ObjDoubleConsumer<R> accumulator,
455 BiConsumer<R, R> combiner);
456
457 /**
458 * Returns the sum of elements in this stream.
459 *
460 * Summation is a special case of a <a
461 * href="package-summary.html#Reduction">reduction</a>. If
462 * floating-point summation were exact, this method would be
463 * equivalent to:
464 *
465 * <pre>{@code
466 * return reduce(0, Double::sum);
467 * }</pre>
468 *
469 * However, since floating-point summation is not exact, the above
470 * code is not necessarily equivalent to the summation computation
471 * done by this method.
472 *
473 * <p>The value of a floating-point sum is a function both
474 * of the input values as well as the order of addition
475 * operations. The order of addition operations of this method is
476 * intentionally not defined to allow for implementation
477 * flexibility to improve the speed and accuracy of the computed
478 * result.
479 *
480 * In particular, this method may be implemented using compensated
481 * summation or other technique to reduce the error bound in the
482 * numerical sum compared to a simple summation of {@code double}
483 * values.
484 *
485 * <p>If any stream element is a NaN or the intermediate sum is at
486 * any point a NaN, then the final sum will be NaN.
487 *
488 * If the stream elements contain infinities of opposite sign, the
489 * final sum will be NaN.
490 *
491 * It is possible for intermediate sums of finite values to
492 * overflow into opposite-signed infinities; if that occurs, the
493 * final sum will be NaN even if the stream elements are all
494 * finite.
495 *
496 * If the exact sum is infinite, a properly-signed infinity is
497 * returned.
498 *
499 * If all the stream elements are zero, the sign of zero is
500 * <em>not</em> guaranteed to be preserved in the final sum.
501 *
502 * <p>This is a <a href="package-summary.html#StreamOps">terminal
503 * operation</a>.
504 *
505 * @apiNote Elements sorted by increasing absolute magnitude tend
506 * to yield more accurate results.
507 *
508 * @return the sum of elements in this stream
509 */
510 double sum();
511
512 /**
513 * Returns an {@code OptionalDouble} describing the minimum element of this
514 * stream, or an empty OptionalDouble if this stream is empty. The minimum
515 * element will be {@code Double.NaN} if any stream element was NaN. Unlike
516 * the numerical comparison operators, this method considers negative zero
517 * to be strictly smaller than positive zero. This is a special case of a
518 * <a href="package-summary.html#Reduction">reduction</a> and is
519 * equivalent to:
520 * <pre>{@code
521 * return reduce(Double::min);
522 * }</pre>
523 *
524 * <p>This is a <a href="package-summary.html#StreamOps">terminal
525 * operation</a>.
526 *
527 * @return an {@code OptionalDouble} containing the minimum element of this
528 * stream, or an empty optional if the stream is empty
529 */
530 OptionalDouble min();
531
532 /**
533 * Returns an {@code OptionalDouble} describing the maximum element of this
534 * stream, or an empty OptionalDouble if this stream is empty. The maximum
535 * element will be {@code Double.NaN} if any stream element was NaN. Unlike
536 * the numerical comparison operators, this method considers negative zero
537 * to be strictly smaller than positive zero. This is a
538 * special case of a
539 * <a href="package-summary.html#Reduction">reduction</a> and is
540 * equivalent to:
541 * <pre>{@code
542 * return reduce(Double::max);
543 * }</pre>
544 *
545 * <p>This is a <a href="package-summary.html#StreamOps">terminal
546 * operation</a>.
547 *
548 * @return an {@code OptionalDouble} containing the maximum element of this
549 * stream, or an empty optional if the stream is empty
550 */
551 OptionalDouble max();
552
553 /**
554 * Returns the count of elements in this stream. This is a special case of
555 * a <a href="package-summary.html#Reduction">reduction</a> and is
556 * equivalent to:
557 * <pre>{@code
558 * return mapToLong(e -> 1L).sum();
559 * }</pre>
560 *
561 * <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>.
562 *
563 * @return the count of elements in this stream
564 */
565 long count();
566
567 /**
568 * Returns an {@code OptionalDouble} describing the arithmetic
569 * mean of elements of this stream, or an empty optional if this
570 * stream is empty.
571 *
572 * <p>The average returned can vary depending upon the order in
573 * which values are recorded.
574 *
575 * This method may be implemented using compensated summation or
576 * other technique to reduce the error bound in the {@link #sum
577 * numerical sum} used to compute the average.
578 *
579 * <p>This method can return a NaN or infinite result in the same
580 * kind of numerical situations as {@linkplain #sum() the sum} can
581 * be NaN or infinite, respectively.
582 *
583 * <p>The average is a special case of a <a
584 * href="package-summary.html#Reduction">reduction</a>.
585 *
586 * <p>This is a <a href="package-summary.html#StreamOps">terminal
587 * operation</a>.
588 *
589 * @apiNote Elements sorted by increasing absolute magnitude tend
590 * to yield more accurate results.
591 *
592 * @return an {@code OptionalDouble} containing the average element of this
593 * stream, or an empty optional if the stream is empty
594 */
595 OptionalDouble average();
596
597 /**
598 * Returns a {@code DoubleSummaryStatistics} describing various summary data
599 * about the elements of this stream. This is a special
600 * case of a <a href="package-summary.html#Reduction">reduction</a>.
601 *
602 * <p>This is a <a href="package-summary.html#StreamOps">terminal
603 * operation</a>.
604 *
605 * @return a {@code DoubleSummaryStatistics} describing various summary data
606 * about the elements of this stream
607 */
608 DoubleSummaryStatistics summaryStatistics();
609
610 /**
611 * Returns whether any elements of this stream match the provided
612 * predicate. May not evaluate the predicate on all elements if not
613 * necessary for determining the result. If the stream is empty then
614 * {@code false} is returned and the predicate is not evaluated.
615 *
616 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
617 * terminal operation</a>.
618 *
619 * @apiNote
620 * This method evaluates the <em>existential quantification</em> of the
621 * predicate over the elements of the stream (for some x P(x)).
622 *
623 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
624 * <a href="package-summary.html#Statelessness">stateless</a>
625 * predicate to apply to elements of this stream
626 * @return {@code true} if any elements of the stream match the provided
627 * predicate, otherwise {@code false}
628 */
629 boolean anyMatch(DoublePredicate predicate);
630
631 /**
632 * Returns whether all 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. If the stream is empty then {@code true} is
635 * returned and the predicate is not evaluated.
636 *
637 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
638 * terminal operation</a>.
639 *
640 * @apiNote
641 * This method evaluates the <em>universal quantification</em> of the
642 * predicate over the elements of the stream (for all x P(x)). If the
643 * stream is empty, the quantification is said to be <em>vacuously
644 * satisfied</em> and is always {@code true} (regardless of P(x)).
645 *
646 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
647 * <a href="package-summary.html#Statelessness">stateless</a>
648 * predicate to apply to elements of this stream
649 * @return {@code true} if either all elements of the stream match the
650 * provided predicate or the stream is empty, otherwise {@code false}
651 */
652 boolean allMatch(DoublePredicate predicate);
653
654 /**
655 * Returns whether no elements of this stream match the provided predicate.
656 * May not evaluate the predicate on all elements if not necessary for
657 * determining the result. If the stream is empty then {@code true} is
658 * returned and the predicate is not evaluated.
659 *
660 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
661 * terminal operation</a>.
662 *
663 * @apiNote
664 * This method evaluates the <em>universal quantification</em> of the
665 * negated predicate over the elements of the stream (for all x ~P(x)). If
666 * the stream is empty, the quantification is said to be vacuously satisfied
667 * and is always {@code true}, regardless of P(x).
668 *
669 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
670 * <a href="package-summary.html#Statelessness">stateless</a>
671 * predicate to apply to elements of this stream
672 * @return {@code true} if either no elements of the stream match the
673 * provided predicate or the stream is empty, otherwise {@code false}
674 */
675 boolean noneMatch(DoublePredicate predicate);
676
677 /**
678 * Returns an {@link OptionalDouble} describing the first element of this
679 * stream, or an empty {@code OptionalDouble} if the stream is empty. If
680 * the stream has no encounter order, then any element may be returned.
681 *
682 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
683 * terminal operation</a>.
684 *
685 * @return an {@code OptionalDouble} describing the first element of this
686 * stream, or an empty {@code OptionalDouble} if the stream is empty
687 */
688 OptionalDouble findFirst();
689
690 /**
691 * Returns an {@link OptionalDouble} describing some element of the stream,
692 * or an empty {@code OptionalDouble} if the stream is empty.
693 *
694 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
695 * terminal operation</a>.
696 *
697 * <p>The behavior of this operation is explicitly nondeterministic; it is
698 * free to select any element in the stream. This is to allow for maximal
699 * performance in parallel operations; the cost is that multiple invocations
700 * on the same source may not return the same result. (If a stable result
701 * is desired, use {@link #findFirst()} instead.)
702 *
703 * @return an {@code OptionalDouble} describing some element of this stream,
704 * or an empty {@code OptionalDouble} if the stream is empty
705 * @see #findFirst()
706 */
707 OptionalDouble findAny();
708
709 /**
710 * Returns a {@code Stream} consisting of the elements of this stream,
711 * boxed to {@code Double}.
712 *
713 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
714 * operation</a>.
715 *
716 * @return a {@code Stream} consistent of the elements of this stream,
717 * each boxed to a {@code Double}
718 */
719 Stream<Double> boxed();
720
721 @Override
722 DoubleStream sequential();
723
724 @Override
725 DoubleStream parallel();
726
727 @Override
728 PrimitiveIterator.OfDouble iterator();
729
730 @Override
731 Spliterator.OfDouble spliterator();
732
733
734 // Static factories
735
736 /**
737 * Returns a builder for a {@code DoubleStream}.
738 *
739 * @return a stream builder
740 */
741 public static Builder builder() {
742 return new Streams.DoubleStreamBuilderImpl();
743 }
744
745 /**
746 * Returns an empty sequential {@code DoubleStream}.
747 *
748 * @return an empty sequential stream
749 */
750 public static DoubleStream empty() {
751 return StreamSupport.doubleStream(Spliterators.emptyDoubleSpliterator(), false);
752 }
753
754 /**
755 * Returns a sequential {@code DoubleStream} containing a single element.
756 *
757 * @param t the single element
758 * @return a singleton sequential stream
759 */
760 public static DoubleStream of(double t) {
761 return StreamSupport.doubleStream(new Streams.DoubleStreamBuilderImpl(t), false);
762 }
763
764 /**
765 * Returns a sequential ordered stream whose elements are the specified values.
766 *
767 * @param values the elements of the new stream
768 * @return the new stream
769 */
770 public static DoubleStream of(double... values) {
771 return Arrays.stream(values);
772 }
773
774 /**
775 * Returns an infinite sequential ordered {@code DoubleStream} produced by iterative
776 * application of a function {@code f} to an initial element {@code seed},
777 * producing a {@code Stream} consisting of {@code seed}, {@code f(seed)},
778 * {@code f(f(seed))}, etc.
779 *
780 * <p>The first element (position {@code 0}) in the {@code DoubleStream}
781 * will be the provided {@code seed}. For {@code n > 0}, the element at
782 * position {@code n}, will be the result of applying the function {@code f}
783 * to the element at position {@code n - 1}.
784 *
785 * @param seed the initial element
786 * @param f a function to be applied to to the previous element to produce
787 * a new element
788 * @return a new sequential {@code DoubleStream}
789 */
790 public static DoubleStream iterate(final double seed, final DoubleUnaryOperator f) {
791 Objects.requireNonNull(f);
792 final PrimitiveIterator.OfDouble iterator = new PrimitiveIterator.OfDouble() {
793 double t = seed;
794
795 @Override
796 public boolean hasNext() {
797 return true;
798 }
799
800 @Override
801 public double nextDouble() {
802 double v = t;
803 t = f.applyAsDouble(t);
804 return v;
805 }
806 };
807 return StreamSupport.doubleStream(Spliterators.spliteratorUnknownSize(
808 iterator,
809 Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), false);
810 }
811
812 /**
813 * Returns an infinite sequential unordered stream where each element is
814 * generated by the provided {@code DoubleSupplier}. This is suitable for
815 * generating constant streams, streams of random elements, etc.
816 *
817 * @param s the {@code DoubleSupplier} for generated elements
818 * @return a new infinite sequential unordered {@code DoubleStream}
819 */
820 public static DoubleStream generate(DoubleSupplier s) {
821 Objects.requireNonNull(s);
822 return StreamSupport.doubleStream(
823 new StreamSpliterators.InfiniteSupplyingSpliterator.OfDouble(Long.MAX_VALUE, s), false);
824 }
825
826 /**
827 * Creates a lazily concatenated stream whose elements are all the
828 * elements of the first stream followed by all the elements of the
829 * second stream. The resulting stream is ordered if both
830 * of the input streams are ordered, and parallel if either of the input
831 * streams is parallel. When the resulting stream is closed, the close
832 * handlers for both input streams are invoked.
833 *
834 * @implNote
835 * Use caution when constructing streams from repeated concatenation.
836 * Accessing an element of a deeply concatenated stream can result in deep
837 * call chains, or even {@code StackOverflowException}.
838 *
839 * @param a the first stream
840 * @param b the second stream
841 * @return the concatenation of the two input streams
842 */
843 public static DoubleStream concat(DoubleStream a, DoubleStream b) {
844 Objects.requireNonNull(a);
845 Objects.requireNonNull(b);
846
847 Spliterator.OfDouble split = new Streams.ConcatSpliterator.OfDouble(
848 a.spliterator(), b.spliterator());
849 DoubleStream stream = StreamSupport.doubleStream(split, a.isParallel() || b.isParallel());
850 return stream.onClose(Streams.composedClose(a, b));
851 }
852
853 /**
854 * A mutable builder for a {@code DoubleStream}.
855 *
856 * <p>A stream builder has a lifecycle, which starts in a building
857 * phase, during which elements can be added, and then transitions to a built
858 * phase, after which elements may not be added. The built phase
859 * begins when the {@link #build()} method is called, which creates an
860 * ordered stream whose elements are the elements that were added to the
861 * stream builder, in the order they were added.
862 *
863 * @see DoubleStream#builder()
864 * @since 1.8
865 */
866 public interface Builder extends DoubleConsumer {
867
868 /**
869 * Adds an element to the stream being built.
870 *
871 * @throws IllegalStateException if the builder has already transitioned
872 * to the built state
873 */
874 @Override
875 void accept(double t);
876
877 /**
878 * Adds an element to the stream being built.
879 *
880 * @implSpec
881 * The default implementation behaves as if:
882 * <pre>{@code
883 * accept(t)
884 * return this;
885 * }</pre>
886 *
887 * @param t the element to add
888 * @return {@code this} builder
889 * @throws IllegalStateException if the builder has already transitioned
890 * to the built state
891 */
892 default Builder add(double t) {
893 accept(t);
894 return this;
895 }
896
897 /**
898 * Builds the stream, transitioning this builder to the built state.
899 * An {@code IllegalStateException} is thrown if there are further
900 * attempts to operate on the builder after it has entered the built
901 * state.
902 *
903 * @return the built stream
904 * @throws IllegalStateException if the builder has already transitioned
905 * to the built state
906 */
907 DoubleStream build();
908 }
909 }