1 /*
2 * Copyright (c) 1997, 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
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20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package javany.util;
27
28 import javany.util.function.Predicate;
29
30 import java.util.Objects;
31
32 /**
33 * The root interface in the <i>collection hierarchy</i>. A collection
34 * represents a group of objects, known as its <i>elements</i>. Some
35 * collections allow duplicate elements and others do not. Some are ordered
36 * and others unordered. The JDK does not provide any <i>direct</i>
37 * implementations of this interface: it provides implementations of more
38 * specific subinterfaces like <tt>Set</tt> and <tt>List</tt>. This interface
39 * is typically used to pass collections around and manipulate them where
40 * maximum generality is desired.
41 *
42 * <p><i>Bags</i> or <i>multisets</i> (unordered collections that may contain
43 * duplicate elements) should implement this interface directly.
44 *
45 * <p>All general-purpose <tt>Collection</tt> implementation classes (which
46 * typically implement <tt>Collection</tt> indirectly through one of its
47 * subinterfaces) should provide two "standard" constructors: a void (no
48 * arguments) constructor, which creates an empty collection, and a
49 * constructor with a single argument of type <tt>Collection</tt>, which
50 * creates a new collection with the same elements as its argument. In
51 * effect, the latter constructor allows the user to copy any collection,
52 * producing an equivalent collection of the desired implementation type.
53 * There is no way to enforce this convention (as interfaces cannot contain
54 * constructors) but all of the general-purpose <tt>Collection</tt>
55 * implementations in the Java platform libraries comply.
56 *
57 * <p>The "destructive" methods contained in this interface, that is, the
58 * methods that modify the collection on which they operate, are specified to
59 * throw <tt>UnsupportedOperationException</tt> if this collection does not
60 * support the operation. If this is the case, these methods may, but are not
61 * required to, throw an <tt>UnsupportedOperationException</tt> if the
62 * invocation would have no effect on the collection. For example, invoking
63 * the {@link #addAll(Collection)} method on an unmodifiable collection may,
64 * but is not required to, throw the exception if the collection to be added
65 * is empty.
66 *
67 * <p><a name="optional-restrictions">
68 * Some collection implementations have restrictions on the elements that
69 * they may contain.</a> For example, some implementations prohibit null elements,
70 * and some have restrictions on the types of their elements. Attempting to
71 * add an ineligible element throws an unchecked exception, typically
72 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting
73 * to query the presence of an ineligible element may throw an exception,
74 * or it may simply return false; some implementations will exhibit the former
75 * behavior and some will exhibit the latter. More generally, attempting an
76 * operation on an ineligible element whose completion would not result in
77 * the insertion of an ineligible element into the collection may throw an
78 * exception or it may succeed, at the option of the implementation.
79 * Such exceptions are marked as "optional" in the specification for this
80 * interface.
81 *
82 * <p>It is up to each collection to determine its own synchronization
83 * policy. In the absence of a stronger guarantee by the
84 * implementation, undefined behavior may result from the invocation
85 * of any method on a collection that is being mutated by another
86 * thread; this includes direct invocations, passing the collection to
87 * a method that might perform invocations, and using an existing
88 * iterator to examine the collection.
89 *
90 * <p>Many methods in Collections Framework interfaces are defined in
91 * terms of the {@link Object#equals(Object) equals} method. For example,
92 * the specification for the {@link #contains(Object) contains(Object o)}
93 * method says: "returns <tt>true</tt> if and only if this collection
94 * contains at least one element <tt>e</tt> such that
95 * <tt>(o==null ? e==null : o.equals(e))</tt>." This specification should
96 * <i>not</i> be construed to imply that invoking <tt>Collection.contains</tt>
97 * with a non-null argument <tt>o</tt> will cause <tt>o.equals(e)</tt> to be
98 * invoked for any element <tt>e</tt>. Implementations are free to implement
99 * optimizations whereby the <tt>equals</tt> invocation is avoided, for
100 * example, by first comparing the hash codes of the two elements. (The
101 * {@link Object#hashCode()} specification guarantees that two objects with
102 * unequal hash codes cannot be equal.) More generally, implementations of
103 * the various Collections Framework interfaces are free to take advantage of
104 * the specified behavior of underlying {@link Object} methods wherever the
105 * implementor deems it appropriate.
106 *
107 * <p>Some collection operations which perform recursive traversal of the
108 * collection may fail with an exception for self-referential instances where
109 * the collection directly or indirectly contains itself. This includes the
110 * {@code clone()}, {@code equals()}, {@code hashCode()} and {@code toString()}
111 * methods. Implementations may optionally handle the self-referential scenario,
112 * however most current implementations do not do so.
113 *
114 * <p>This interface is a member of the
115 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
116 * Java Collections Framework</a>.
117 *
118 * @implSpec
119 * The default method implementations (inherited or otherwise) do not apply any
120 * synchronization protocol. If a {@code Collection} implementation has a
121 * specific synchronization protocol, then it must override default
122 * implementations to apply that protocol.
123 *
124 * @param <E> the type of elements in this collection
125 *
126 * @author Josh Bloch
127 * @author Neal Gafter
128 * @see Set
129 * @see List
130 * @see Map
131 * @see SortedSet
132 * @see SortedMap
133 * @see HashSet
134 * @see TreeSet
135 * @see ArrayList
136 * @see LinkedList
137 * @see Vector
138 * @see Collections
139 * @see Arrays
140 * @see AbstractCollection
141 * @since 1.2
142 */
143
144 public interface Collection<any E> extends javany.lang.Iterable<E> {
145 // Query Operations
146
147 /**
148 * Returns the number of elements in this collection. If this collection
149 * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
150 * <tt>Integer.MAX_VALUE</tt>.
151 *
152 * @return the number of elements in this collection
153 */
154 int size();
155
156 /**
157 * Returns <tt>true</tt> if this collection contains no elements.
158 *
159 * @return <tt>true</tt> if this collection contains no elements
160 */
161 boolean isEmpty();
162
163 /**
164 * Returns <tt>true</tt> if this collection contains the specified element.
165 * More formally, returns <tt>true</tt> if and only if this collection
166 * contains at least one element <tt>e</tt> such that
167 * <tt>(o==null ? e==null : o.equals(e))</tt>.
168 *
169 * @param o element whose presence in this collection is to be tested
170 * @return <tt>true</tt> if this collection contains the specified
171 * element
172 * @throws ClassCastException if the type of the specified element
173 * is incompatible with this collection
174 * (<a href="#optional-restrictions">optional</a>)
175 * @throws NullPointerException if the specified element is null and this
176 * collection does not permit null elements
177 * (<a href="#optional-restrictions">optional</a>)
178 */
179 boolean contains(Object o);
180
181 default boolean containsElement(E e) {
182 Iterator<E> it = iterator();
183 while (it.hasNext())
184 if (Any.equals(e, it.next()))
185 return true;
186 return false;
187 }
188
189 /**
190 * Returns an iterator over the elements in this collection. There are no
191 * guarantees concerning the order in which the elements are returned
192 * (unless this collection is an instance of some class that provides a
193 * guarantee).
194 *
195 * @return an <tt>Iterator</tt> over the elements in this collection
196 */
197 Iterator<E> iterator();
198
199 /**
200 * Returns an array containing all of the elements in this collection.
201 * If this collection makes any guarantees as to what order its elements
202 * are returned by its iterator, this method must return the elements in
203 * the same order.
204 *
205 * <p>The returned array will be "safe" in that no references to it are
206 * maintained by this collection. (In other words, this method must
207 * allocate a new array even if this collection is backed by an array).
208 * The caller is thus free to modify the returned array.
209 *
210 * <p>This method acts as bridge between array-based and collection-based
211 * APIs.
212 *
213 * @return an array containing all of the elements in this collection
214 */
215 Object[] toArray();
216
217 /**
218 * Returns an array containing all of the elements in this collection;
219 * the runtime type of the returned array is that of the specified array.
220 * If the collection fits in the specified array, it is returned therein.
221 * Otherwise, a new array is allocated with the runtime type of the
222 * specified array and the size of this collection.
223 *
224 * <p>If this collection fits in the specified array with room to spare
225 * (i.e., the array has more elements than this collection), the element
226 * in the array immediately following the end of the collection is set to
227 * <tt>null</tt>. (This is useful in determining the length of this
228 * collection <i>only</i> if the caller knows that this collection does
229 * not contain any <tt>null</tt> elements.)
230 *
231 * <p>If this collection makes any guarantees as to what order its elements
232 * are returned by its iterator, this method must return the elements in
233 * the same order.
234 *
235 * <p>Like the {@link #toArray()} method, this method acts as bridge between
236 * array-based and collection-based APIs. Further, this method allows
237 * precise control over the runtime type of the output array, and may,
238 * under certain circumstances, be used to save allocation costs.
239 *
240 * <p>Suppose <tt>x</tt> is a collection known to contain only strings.
241 * The following code can be used to dump the collection into a newly
242 * allocated array of <tt>String</tt>:
243 *
244 * <pre>
245 * String[] y = x.toArray(new String[0]);</pre>
246 *
247 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
248 * <tt>toArray()</tt>.
249 *
250 * @param <T> the runtime type of the array to contain the collection
251 * @param a the array into which the elements of this collection are to be
252 * stored, if it is big enough; otherwise, a new array of the same
253 * runtime type is allocated for this purpose.
254 * @return an array containing all of the elements in this collection
255 * @throws ArrayStoreException if the runtime type of the specified array
256 * is not a supertype of the runtime type of every element in
257 * this collection
258 * @throws NullPointerException if the specified array is null
259 */
260 <any T> T[] toArray(T[] a);
261
262 // Modification Operations
263
264 /**
265 * Ensures that this collection contains the specified element (optional
266 * operation). Returns <tt>true</tt> if this collection changed as a
267 * result of the call. (Returns <tt>false</tt> if this collection does
268 * not permit duplicates and already contains the specified element.)<p>
269 *
270 * Collections that support this operation may place limitations on what
271 * elements may be added to this collection. In particular, some
272 * collections will refuse to add <tt>null</tt> elements, and others will
273 * impose restrictions on the type of elements that may be added.
274 * Collection classes should clearly specify in their documentation any
275 * restrictions on what elements may be added.<p>
276 *
277 * If a collection refuses to add a particular element for any reason
278 * other than that it already contains the element, it <i>must</i> throw
279 * an exception (rather than returning <tt>false</tt>). This preserves
280 * the invariant that a collection always contains the specified element
281 * after this call returns.
282 *
283 * @param e element whose presence in this collection is to be ensured
284 * @return <tt>true</tt> if this collection changed as a result of the
285 * call
286 * @throws UnsupportedOperationException if the <tt>add</tt> operation
287 * is not supported by this collection
288 * @throws ClassCastException if the class of the specified element
289 * prevents it from being added to this collection
290 * @throws NullPointerException if the specified element is null and this
291 * collection does not permit null elements
292 * @throws IllegalArgumentException if some property of the element
293 * prevents it from being added to this collection
294 * @throws IllegalStateException if the element cannot be added at this
295 * time due to insertion restrictions
296 */
297 boolean add(E e);
298
299 /**
300 * Removes a single instance of the specified element from this
301 * collection, if it is present (optional operation). More formally,
302 * removes an element <tt>e</tt> such that
303 * <tt>(o==null ? e==null : o.equals(e))</tt>, if
304 * this collection contains one or more such elements. Returns
305 * <tt>true</tt> if this collection contained the specified element (or
306 * equivalently, if this collection changed as a result of the call).
307 *
308 * @param o element to be removed from this collection, if present
309 * @return <tt>true</tt> if an element was removed as a result of this call
310 * @throws ClassCastException if the type of the specified element
311 * is incompatible with this collection
312 * (<a href="#optional-restrictions">optional</a>)
313 * @throws NullPointerException if the specified element is null and this
314 * collection does not permit null elements
315 * (<a href="#optional-restrictions">optional</a>)
316 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
317 * is not supported by this collection
318 */
319 boolean remove(Object o);
320
321 default boolean removeElement(E e) {
322 Iterator<E> it = iterator();
323 while (it.hasNext()) {
324 if (Any.equals(e, it.next())) {
325 it.remove();
326 return true;
327 }
328 }
329 return false;
330 }
331
332 // Bulk Operations
333
334 /**
335 * Returns <tt>true</tt> if this collection contains all of the elements
336 * in the specified collection.
337 *
338 * @param c collection to be checked for containment in this collection
339 * @return <tt>true</tt> if this collection contains all of the elements
340 * in the specified collection
341 * @throws ClassCastException if the types of one or more elements
342 * in the specified collection are incompatible with this
343 * collection
344 * (<a href="#optional-restrictions">optional</a>)
345 * @throws NullPointerException if the specified collection contains one
346 * or more null elements and this collection does not permit null
347 * elements
348 * (<a href="#optional-restrictions">optional</a>),
349 * or if the specified collection is null.
350 * @see #contains(Object)
351 */
352 boolean containsAll(Collection<?> c);
353
354 default boolean containsAllElements(Collection<? extends E> c) {
355 Iterator<? extends E> it = c.iterator();
356 while (it.hasNext()) {
357 if (!containsElement(it.next())) {
358 return false;
359 }
360 }
361 return true;
362 }
363
364 /**
365 * Adds all of the elements in the specified collection to this collection
366 * (optional operation). The behavior of this operation is undefined if
367 * the specified collection is modified while the operation is in progress.
368 * (This implies that the behavior of this call is undefined if the
369 * specified collection is this collection, and this collection is
370 * nonempty.)
371 *
372 * @param c collection containing elements to be added to this collection
373 * @return <tt>true</tt> if this collection changed as a result of the call
374 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
375 * is not supported by this collection
376 * @throws ClassCastException if the class of an element of the specified
377 * collection prevents it from being added to this collection
378 * @throws NullPointerException if the specified collection contains a
379 * null element and this collection does not permit null elements,
380 * or if the specified collection is null
381 * @throws IllegalArgumentException if some property of an element of the
382 * specified collection prevents it from being added to this
383 * collection
384 * @throws IllegalStateException if not all the elements can be added at
385 * this time due to insertion restrictions
386 * @see #add(Object)
387 */
388 boolean addAll(Collection<? extends E> c);
389
390 /**
391 * Removes all of this collection's elements that are also contained in the
392 * specified collection (optional operation). After this call returns,
393 * this collection will contain no elements in common with the specified
394 * collection.
395 *
396 * @param c collection containing elements to be removed from this collection
397 * @return <tt>true</tt> if this collection changed as a result of the
398 * call
399 * @throws UnsupportedOperationException if the <tt>removeAll</tt> method
400 * is not supported by this collection
401 * @throws ClassCastException if the types of one or more elements
402 * in this collection are incompatible with the specified
403 * collection
404 * (<a href="#optional-restrictions">optional</a>)
405 * @throws NullPointerException if this collection contains one or more
406 * null elements and the specified collection does not support
407 * null elements
408 * (<a href="#optional-restrictions">optional</a>),
409 * or if the specified collection is null
410 * @see #remove(Object)
411 * @see #contains(Object)
412 */
413 boolean removeAll(Collection<?> c);
414
415 default boolean removeAllElements(Collection<E> c) {
416 Objects.requireNonNull(c);
417 boolean modified = false;
418 Iterator<E> it = iterator();
419 while (it.hasNext()) {
420 if (c.containsElement(it.next())) {
421 it.remove();
422 modified = true;
423 }
424 }
425 return modified;
426 }
427
428 /**
429 * Removes all of the elements of this collection that satisfy the given
430 * predicate. Errors or runtime exceptions thrown during iteration or by
431 * the predicate are relayed to the caller.
432 *
433 * @implSpec
434 * The default implementation traverses all elements of the collection using
435 * its {@link #iterator}. Each matching element is removed using
436 * {@link Iterator#remove()}. If the collection's iterator does not
437 * support removal then an {@code UnsupportedOperationException} will be
438 * thrown on the first matching element.
439 *
440 * @param filter a predicate which returns {@code true} for elements to be
441 * removed
442 * @return {@code true} if any elements were removed
443 * @throws NullPointerException if the specified filter is null
444 * @throws UnsupportedOperationException if elements cannot be removed
445 * from this collection. Implementations may throw this exception if a
446 * matching element cannot be removed or if, in general, removal is not
447 * supported.
448 * @since 1.8
449 */
450 default boolean removeIf(Predicate<? super E> filter) {
451 Objects.requireNonNull(filter);
452 boolean removed = false;
453 final Iterator<E> each = iterator();
454 while (each.hasNext()) {
455 if (filter.test(each.next())) {
456 each.remove();
457 removed = true;
458 }
459 }
460 return removed;
461 }
462
463 /**
464 * Retains only the elements in this collection that are contained in the
465 * specified collection (optional operation). In other words, removes from
466 * this collection all of its elements that are not contained in the
467 * specified collection.
468 *
469 * @param c collection containing elements to be retained in this collection
470 * @return <tt>true</tt> if this collection changed as a result of the call
471 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
472 * is not supported by this collection
473 * @throws ClassCastException if the types of one or more elements
474 * in this collection are incompatible with the specified
475 * collection
476 * (<a href="#optional-restrictions">optional</a>)
477 * @throws NullPointerException if this collection contains one or more
478 * null elements and the specified collection does not permit null
479 * elements
480 * (<a href="#optional-restrictions">optional</a>),
481 * or if the specified collection is null
482 * @see #remove(Object)
483 * @see #contains(Object)
484 */
485 boolean retainAll(Collection<?> c);
486
487 default boolean retainAllElements(Collection<E> c) {
488 Objects.requireNonNull(c);
489 boolean modified = false;
490 Iterator<E> it = iterator();
491 while (it.hasNext()) {
492 if (!c.containsElement(it.next())) {
493 it.remove();
494 modified = true;
495 }
496 }
497 return modified;
498 }
499
500 /**
501 * Removes all of the elements from this collection (optional operation).
502 * The collection will be empty after this method returns.
503 *
504 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
505 * is not supported by this collection
506 */
507 void clear();
508
509
510 // Comparison and hashing
511
512 /**
513 * Compares the specified object with this collection for equality. <p>
514 *
515 * While the <tt>Collection</tt> interface adds no stipulations to the
516 * general contract for the <tt>Object.equals</tt>, programmers who
517 * implement the <tt>Collection</tt> interface "directly" (in other words,
518 * create a class that is a <tt>Collection</tt> but is not a <tt>Set</tt>
519 * or a <tt>List</tt>) must exercise care if they choose to override the
520 * <tt>Object.equals</tt>. It is not necessary to do so, and the simplest
521 * course of action is to rely on <tt>Object</tt>'s implementation, but
522 * the implementor may wish to implement a "value comparison" in place of
523 * the default "reference comparison." (The <tt>List</tt> and
524 * <tt>Set</tt> interfaces mandate such value comparisons.)<p>
525 *
526 * The general contract for the <tt>Object.equals</tt> method states that
527 * equals must be symmetric (in other words, <tt>a.equals(b)</tt> if and
528 * only if <tt>b.equals(a)</tt>). The contracts for <tt>List.equals</tt>
529 * and <tt>Set.equals</tt> state that lists are only equal to other lists,
530 * and sets to other sets. Thus, a custom <tt>equals</tt> method for a
531 * collection class that implements neither the <tt>List</tt> nor
532 * <tt>Set</tt> interface must return <tt>false</tt> when this collection
533 * is compared to any list or set. (By the same logic, it is not possible
534 * to write a class that correctly implements both the <tt>Set</tt> and
535 * <tt>List</tt> interfaces.)
536 *
537 * @param o object to be compared for equality with this collection
538 * @return <tt>true</tt> if the specified object is equal to this
539 * collection
540 *
541 * @see Object#equals(Object)
542 * @see Set#equals(Object)
543 * @see List#equals(Object)
544 */
545 boolean equals(Object o);
546
547 /**
548 * Returns the hash code value for this collection. While the
549 * <tt>Collection</tt> interface adds no stipulations to the general
550 * contract for the <tt>Object.hashCode</tt> method, programmers should
551 * take note that any class that overrides the <tt>Object.equals</tt>
552 * method must also override the <tt>Object.hashCode</tt> method in order
553 * to satisfy the general contract for the <tt>Object.hashCode</tt> method.
554 * In particular, <tt>c1.equals(c2)</tt> implies that
555 * <tt>c1.hashCode()==c2.hashCode()</tt>.
556 *
557 * @return the hash code value for this collection
558 *
559 * @see Object#hashCode()
560 * @see Object#equals(Object)
561 */
562 int hashCode();
563
564 /**
565 * Creates a {@link Spliterator} over the elements in this collection.
566 *
567 * Implementations should document characteristic values reported by the
568 * spliterator. Such characteristic values are not required to be reported
569 * if the spliterator reports {@link Spliterator#SIZED} and this collection
570 * contains no elements.
571 *
572 * <p>The default implementation should be overridden by subclasses that
573 * can return a more efficient spliterator. In order to
574 * preserve expected laziness behavior for the {@link #stream()} and
575 * {@link #parallelStream()} methods, spliterators should either have the
576 * characteristic of {@code IMMUTABLE} or {@code CONCURRENT}, or be
577 * <em><a href="Spliterator.html#binding">late-binding</a></em>.
578 * If none of these is practical, the overriding class should describe the
579 * spliterator's documented policy of binding and structural interference,
580 * and should override the {@link #stream()} and {@link #parallelStream()}
581 * methods to create streams using a {@code Supplier} of the spliterator,
582 * as in:
583 * <pre>{@code
584 * Stream<E> s = StreamSupport.stream(() -> spliterator(), spliteratorCharacteristics)
585 * }</pre>
586 * <p>These requirements ensure that streams produced by the
587 * {@link #stream()} and {@link #parallelStream()} methods will reflect the
588 * contents of the collection as of initiation of the terminal stream
589 * operation.
590 *
591 * @implSpec
592 * The default implementation creates a
593 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
594 * from the collections's {@code Iterator}. The spliterator inherits the
595 * <em>fail-fast</em> properties of the collection's iterator.
596 * <p>
597 * The created {@code Spliterator} reports {@link Spliterator#SIZED}.
598 *
599 * @implNote
600 * The created {@code Spliterator} additionally reports
601 * {@link Spliterator#SUBSIZED}.
602 *
603 * <p>If a spliterator covers no elements then the reporting of additional
604 * characteristic values, beyond that of {@code SIZED} and {@code SUBSIZED},
605 * does not aid clients to control, specialize or simplify computation.
606 * However, this does enable shared use of an immutable and empty
607 * spliterator instance (see {@link Spliterators#emptySpliterator()}) for
608 * empty collections, and enables clients to determine if such a spliterator
609 * covers no elements.
610 *
611 * @return a {@code Spliterator} over the elements in this collection
612 * @since 1.8
613 */
614 // @Override
615 // default Spliterator<E> spliterator() {
616 // return Spliterators.spliterator(this, 0);
617 // }
618
619 /**
620 * Returns a sequential {@code Stream} with this collection as its source.
621 *
622 * <p>This method should be overridden when the {@link #spliterator()}
623 * method cannot return a spliterator that is {@code IMMUTABLE},
624 * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
625 * for details.)
626 *
627 * @implSpec
628 * The default implementation creates a sequential {@code Stream} from the
629 * collection's {@code Spliterator}.
630 *
631 * @return a sequential {@code Stream} over the elements in this collection
632 * @since 1.8
633 */
634 // default Stream<E> stream() {
635 // return StreamSupport.stream(spliterator(), false);
636 // }
637
638 /**
639 * Returns a possibly parallel {@code Stream} with this collection as its
640 * source. It is allowable for this method to return a sequential stream.
641 *
642 * <p>This method should be overridden when the {@link #spliterator()}
643 * method cannot return a spliterator that is {@code IMMUTABLE},
644 * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
645 * for details.)
646 *
647 * @implSpec
648 * The default implementation creates a parallel {@code Stream} from the
649 * collection's {@code Spliterator}.
650 *
651 * @return a possibly parallel {@code Stream} over the elements in this
652 * collection
653 * @since 1.8
654 */
655 // default Stream<E> parallelStream() {
656 // return StreamSupport.stream(spliterator(), true);
657 // }
658 }