1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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15 * accompanied this code).
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25
26 package java.util;
27
28 import java.util.function.Predicate;
29 import java.util.stream.Stream;
30 import java.util.stream.StreamSupport;
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 {@code Set} and {@code List}. 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 {@code Collection} implementation classes (which
46 * typically implement {@code Collection} 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 {@code Collection}, 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 {@code Collection}
55 * implementations in the Java platform libraries comply.
56 *
57 * <p>Certain methods are specified to be
58 * <i>optional</i>. If a collection implementation doesn't implement a
59 * particular operation, it should define the corresponding method to throw
60 * {@code UnsupportedOperationException}. Such methods are marked "optional
61 * operation" in method specifications of the collections interfaces.
62 *
63 * <p><a id="optional-restrictions"></a>Some collection implementations
64 * have restrictions on the elements that they may contain.
65 * For example, some implementations prohibit null elements,
66 * and some have restrictions on the types of their elements. Attempting to
67 * add an ineligible element throws an unchecked exception, typically
68 * {@code NullPointerException} or {@code ClassCastException}. Attempting
69 * to query the presence of an ineligible element may throw an exception,
70 * or it may simply return false; some implementations will exhibit the former
71 * behavior and some will exhibit the latter. More generally, attempting an
72 * operation on an ineligible element whose completion would not result in
73 * the insertion of an ineligible element into the collection may throw an
74 * exception or it may succeed, at the option of the implementation.
75 * Such exceptions are marked as "optional" in the specification for this
76 * interface.
77 *
78 * <p>It is up to each collection to determine its own synchronization
79 * policy. In the absence of a stronger guarantee by the
80 * implementation, undefined behavior may result from the invocation
81 * of any method on a collection that is being mutated by another
82 * thread; this includes direct invocations, passing the collection to
83 * a method that might perform invocations, and using an existing
84 * iterator to examine the collection.
85 *
86 * <p>Many methods in Collections Framework interfaces are defined in
87 * terms of the {@link Object#equals(Object) equals} method. For example,
88 * the specification for the {@link #contains(Object) contains(Object o)}
89 * method says: "returns {@code true} if and only if this collection
90 * contains at least one element {@code e} such that
91 * {@code (o==null ? e==null : o.equals(e))}." This specification should
92 * <i>not</i> be construed to imply that invoking {@code Collection.contains}
93 * with a non-null argument {@code o} will cause {@code o.equals(e)} to be
94 * invoked for any element {@code e}. Implementations are free to implement
95 * optimizations whereby the {@code equals} invocation is avoided, for
96 * example, by first comparing the hash codes of the two elements. (The
97 * {@link Object#hashCode()} specification guarantees that two objects with
98 * unequal hash codes cannot be equal.) More generally, implementations of
99 * the various Collections Framework interfaces are free to take advantage of
100 * the specified behavior of underlying {@link Object} methods wherever the
101 * implementor deems it appropriate.
102 *
103 * <p>Some collection operations which perform recursive traversal of the
104 * collection may fail with an exception for self-referential instances where
105 * the collection directly or indirectly contains itself. This includes the
106 * {@code clone()}, {@code equals()}, {@code hashCode()} and {@code toString()}
107 * methods. Implementations may optionally handle the self-referential scenario,
108 * however most current implementations do not do so.
109 *
110 * <h2><a id="view">View Collections</a></h2>
111 *
112 * <p>Most collections manage storage for elements they contain. By contrast, <i>view
113 * collections</i> themselves do not store elements, but instead they rely on a
114 * backing collection to store the actual elements. Operations that are not handled
115 * by the view collection itself are delegated to the backing collection. Examples of
116 * view collections include the wrapper collections returned by methods such as
117 * {@link Collections#checkedCollection Collections.checkedCollection},
118 * {@link Collections#synchronizedCollection Collections.synchronizedCollection}, and
119 * {@link Collections#unmodifiableCollection Collections.unmodifiableCollection}.
120 * Other examples of view collections include collections that provide a
121 * different representation of the same elements, for example, as
122 * provided by {@link List#subList List.subList},
123 * {@link NavigableSet#subSet NavigableSet.subSet}, or
124 * {@link Map#entrySet Map.entrySet}.
125 * Any changes made to the backing collection are visible in the view collection.
126 * Correspondingly, any changes made to the view collection — if changes
127 * are permitted — are written through to the backing collection.
128 * Although they technically aren't collections, instances of
129 * {@link Iterator} and {@link ListIterator} can also allow modifications
130 * to be written through to the backing collection, and in some cases,
131 * modifications to the backing collection will be visible to the Iterator
132 * during iteration.
133 *
134 * <h2><a id="unmodifiable">Unmodifiable Collections</a></h2>
135 *
136 * <p>Certain methods of this interface are considered "destructive" and are called
137 * "mutator" methods in that they modify the group of objects contained within
138 * the collection on which they operate. They can be specified to throw
139 * {@code UnsupportedOperationException} if this collection implementation
140 * does not support the operation. Such methods should (but are not required
141 * to) throw an {@code UnsupportedOperationException} if the invocation would
142 * have no effect on the collection. For example, consider a collection that
143 * does not support the {@link #add add} operation. What will happen if the
144 * {@link #addAll addAll} method is invoked on this collection, with an empty
145 * collection as the argument? The addition of zero elements has no effect,
146 * so it is permissible for this collection simply to do nothing and not to throw
147 * an exception. However, it is recommended that such cases throw an exception
148 * unconditionally, as throwing only in certain cases can lead to
149 * programming errors.
150 *
151 * <p>An <i>unmodifiable collection</i> is a collection, all of whose
152 * mutator methods (as defined above) are specified to throw
153 * {@code UnsupportedOperationException}. Such a collection thus cannot be
154 * modified by calling any methods on it. For a collection to be properly
155 * unmodifiable, any view collections derived from it must also be unmodifiable.
156 * For example, if a List is unmodifiable, the List returned by
157 * {@link List#subList List.subList} is also unmodifiable.
158 *
159 * <p>An unmodifiable collection is not necessarily immutable. If the
160 * contained elements are mutable, the entire collection is clearly
161 * mutable, even though it might be unmodifiable. For example, consider
162 * two unmodifiable lists containing mutable elements. The result of calling
163 * {@code list1.equals(list2)} might differ from one call to the next if
164 * the elements had been mutated, even though both lists are unmodifiable.
165 * However, if an unmodifiable collection contains all immutable elements,
166 * it can be considered effectively immutable.
167 *
168 * <h2><a id="unmodview">Unmodifiable View Collections</a></h2>
169 *
170 * <p>An <i>unmodifiable view collection</i> is a collection that is unmodifiable
171 * and that is also a view onto a backing collection. Its mutator methods throw
172 * {@code UnsupportedOperationException}, as described above, while
173 * reading and querying methods are delegated to the backing collection.
174 * The effect is to provide read-only access to the backing collection.
175 * This is useful for a component to provide users with read access to
176 * an internal collection, while preventing them from modifying such
177 * collections unexpectedly. Examples of unmodifiable view collections
178 * are those returned by the
179 * {@link Collections#unmodifiableCollection Collections.unmodifiableCollection},
180 * {@link Collections#unmodifiableList Collections.unmodifiableList}, and
181 * related methods.
182 *
183 * <p>Note that changes to the backing collection might still be possible,
184 * and if they occur, they are visible through the unmodifiable view. Thus,
185 * an unmodifiable view collection is not necessarily immutable. However,
186 * if the backing collection of an unmodifiable view is effectively immutable,
187 * or if the only reference to the backing collection is through an
188 * unmodifiable view, the view can be considered effectively immutable.
189 *
190 * <p>This interface is a member of the
191 * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
192 * Java Collections Framework</a>.
193 *
194 * @implSpec
195 * The default method implementations (inherited or otherwise) do not apply any
196 * synchronization protocol. If a {@code Collection} implementation has a
197 * specific synchronization protocol, then it must override default
198 * implementations to apply that protocol.
199 *
200 * @param <E> the type of elements in this collection
201 *
202 * @author Josh Bloch
203 * @author Neal Gafter
204 * @see Set
205 * @see List
206 * @see Map
207 * @see SortedSet
208 * @see SortedMap
209 * @see HashSet
210 * @see TreeSet
211 * @see ArrayList
212 * @see LinkedList
213 * @see Vector
214 * @see Collections
215 * @see Arrays
216 * @see AbstractCollection
217 * @since 1.2
218 */
219
220 public interface Collection<E> extends Iterable<E> {
221 // Query Operations
222
223 /**
224 * Returns the number of elements in this collection. If this collection
225 * contains more than {@code Integer.MAX_VALUE} elements, returns
226 * {@code Integer.MAX_VALUE}.
227 *
228 * @return the number of elements in this collection
229 */
230 int size();
231
232 /**
233 * Returns {@code true} if this collection contains no elements.
234 *
235 * @return {@code true} if this collection contains no elements
236 */
237 boolean isEmpty();
238
239 /**
240 * Returns {@code true} if this collection contains the specified element.
241 * More formally, returns {@code true} if and only if this collection
242 * contains at least one element {@code e} such that
243 * {@code Objects.equals(o, e)}.
244 *
245 * @param o element whose presence in this collection is to be tested
246 * @return {@code true} if this collection contains the specified
247 * element
248 * @throws ClassCastException if the type of the specified element
249 * is incompatible with this collection
250 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
251 * @throws NullPointerException if the specified element is null and this
252 * collection does not permit null elements
253 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
254 */
255 boolean contains(Object o);
256
257 /**
258 * Returns an iterator over the elements in this collection. There are no
259 * guarantees concerning the order in which the elements are returned
260 * (unless this collection is an instance of some class that provides a
261 * guarantee).
262 *
263 * @return an {@code Iterator} over the elements in this collection
264 */
265 Iterator<E> iterator();
266
267 /**
268 * Returns an array containing all of the elements in this collection.
269 * If this collection makes any guarantees as to what order its elements
270 * are returned by its iterator, this method must return the elements in
271 * the same order. The returned array's {@linkplain Class#getComponentType
272 * runtime component type} is {@code Object}.
273 *
274 * <p>The returned array will be "safe" in that no references to it are
275 * maintained by this collection. (In other words, this method must
276 * allocate a new array even if this collection is backed by an array).
277 * The caller is thus free to modify the returned array.
278 *
279 * <p>This method acts as bridge between array-based and collection-based
280 * APIs.
281 *
282 * @return an array, whose {@linkplain Class#getComponentType runtime component
283 * type} is {@code Object}, containing all of the elements in this collection
284 */
285 Object[] toArray();
286
287 /**
288 * Returns an array containing all of the elements in this collection;
289 * the runtime type of the returned array is that of the specified array.
290 * If the collection fits in the specified array, it is returned therein.
291 * Otherwise, a new array is allocated with the runtime type of the
292 * specified array and the size of this collection.
293 *
294 * <p>If this collection fits in the specified array with room to spare
295 * (i.e., the array has more elements than this collection), the element
296 * in the array immediately following the end of the collection is set to
297 * {@code null}. (This is useful in determining the length of this
298 * collection <i>only</i> if the caller knows that this collection does
299 * not contain any {@code null} elements.)
300 *
301 * <p>If this collection makes any guarantees as to what order its elements
302 * are returned by its iterator, this method must return the elements in
303 * the same order.
304 *
305 * <p>Like the {@link #toArray()} method, this method acts as bridge between
306 * array-based and collection-based APIs. Further, this method allows
307 * precise control over the runtime type of the output array, and may,
308 * under certain circumstances, be used to save allocation costs.
309 *
310 * <p>Suppose {@code x} is a collection known to contain only strings.
311 * The following code can be used to dump the collection into a newly
312 * allocated array of {@code String}:
313 *
314 * <pre>
315 * String[] y = x.toArray(new String[0]);</pre>
316 *
317 * Note that {@code toArray(new Object[0])} is identical in function to
318 * {@code toArray()}.
319 *
320 * @param <T> the component type of the array to contain the collection
321 * @param a the array into which the elements of this collection are to be
322 * stored, if it is big enough; otherwise, a new array of the same
323 * runtime type is allocated for this purpose.
324 * @return an array containing all of the elements in this collection
325 * @throws ArrayStoreException if the runtime type of any element in this
326 * collection is not assignable to the {@linkplain Class#getComponentType
327 * runtime component type} of the specified array
328 * @throws NullPointerException if the specified array is null
329 */
330 <T> T[] toArray(T[] a);
331
332 // Modification Operations
333
334 /**
335 * Ensures that this collection contains the specified element (optional
336 * operation). Returns {@code true} if this collection changed as a
337 * result of the call. (Returns {@code false} if this collection does
338 * not permit duplicates and already contains the specified element.)<p>
339 *
340 * Collections that support this operation may place limitations on what
341 * elements may be added to this collection. In particular, some
342 * collections will refuse to add {@code null} elements, and others will
343 * impose restrictions on the type of elements that may be added.
344 * Collection classes should clearly specify in their documentation any
345 * restrictions on what elements may be added.<p>
346 *
347 * If a collection refuses to add a particular element for any reason
348 * other than that it already contains the element, it <i>must</i> throw
349 * an exception (rather than returning {@code false}). This preserves
350 * the invariant that a collection always contains the specified element
351 * after this call returns.
352 *
353 * @param e element whose presence in this collection is to be ensured
354 * @return {@code true} if this collection changed as a result of the
355 * call
356 * @throws UnsupportedOperationException if the {@code add} operation
357 * is not supported by this collection
358 * @throws ClassCastException if the class of the specified element
359 * prevents it from being added to this collection
360 * @throws NullPointerException if the specified element is null and this
361 * collection does not permit null elements
362 * @throws IllegalArgumentException if some property of the element
363 * prevents it from being added to this collection
364 * @throws IllegalStateException if the element cannot be added at this
365 * time due to insertion restrictions
366 */
367 boolean add(E e);
368
369 /**
370 * Removes a single instance of the specified element from this
371 * collection, if it is present (optional operation). More formally,
372 * removes an element {@code e} such that
373 * {@code Objects.equals(o, e)}, if
374 * this collection contains one or more such elements. Returns
375 * {@code true} if this collection contained the specified element (or
376 * equivalently, if this collection changed as a result of the call).
377 *
378 * @param o element to be removed from this collection, if present
379 * @return {@code true} if an element was removed as a result of this call
380 * @throws ClassCastException if the type of the specified element
381 * is incompatible with this collection
382 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
383 * @throws NullPointerException if the specified element is null and this
384 * collection does not permit null elements
385 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
386 * @throws UnsupportedOperationException if the {@code remove} operation
387 * is not supported by this collection
388 */
389 boolean remove(Object o);
390
391
392 // Bulk Operations
393
394 /**
395 * Returns {@code true} if this collection contains all of the elements
396 * in the specified collection.
397 *
398 * @param c collection to be checked for containment in this collection
399 * @return {@code true} if this collection contains all of the elements
400 * in the specified collection
401 * @throws ClassCastException if the types of one or more elements
402 * in the specified collection are incompatible with this
403 * collection
404 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
405 * @throws NullPointerException if the specified collection contains one
406 * or more null elements and this collection does not permit null
407 * elements
408 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>),
409 * or if the specified collection is null.
410 * @see #contains(Object)
411 */
412 boolean containsAll(Collection<?> c);
413
414 /**
415 * Adds all of the elements in the specified collection to this collection
416 * (optional operation). The behavior of this operation is undefined if
417 * the specified collection is modified while the operation is in progress.
418 * (This implies that the behavior of this call is undefined if the
419 * specified collection is this collection, and this collection is
420 * nonempty.)
421 *
422 * @param c collection containing elements to be added to this collection
423 * @return {@code true} if this collection changed as a result of the call
424 * @throws UnsupportedOperationException if the {@code addAll} operation
425 * is not supported by this collection
426 * @throws ClassCastException if the class of an element of the specified
427 * collection prevents it from being added to this collection
428 * @throws NullPointerException if the specified collection contains a
429 * null element and this collection does not permit null elements,
430 * or if the specified collection is null
431 * @throws IllegalArgumentException if some property of an element of the
432 * specified collection prevents it from being added to this
433 * collection
434 * @throws IllegalStateException if not all the elements can be added at
435 * this time due to insertion restrictions
436 * @see #add(Object)
437 */
438 boolean addAll(Collection<? extends E> c);
439
440 /**
441 * Removes all of this collection's elements that are also contained in the
442 * specified collection (optional operation). After this call returns,
443 * this collection will contain no elements in common with the specified
444 * collection.
445 *
446 * @param c collection containing elements to be removed from this collection
447 * @return {@code true} if this collection changed as a result of the
448 * call
449 * @throws UnsupportedOperationException if the {@code removeAll} method
450 * is not supported by this collection
451 * @throws ClassCastException if the types of one or more elements
452 * in this collection are incompatible with the specified
453 * collection
454 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
455 * @throws NullPointerException if this collection contains one or more
456 * null elements and the specified collection does not support
457 * null elements
458 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>),
459 * or if the specified collection is null
460 * @see #remove(Object)
461 * @see #contains(Object)
462 */
463 boolean removeAll(Collection<?> c);
464
465 /**
466 * Removes all of the elements of this collection that satisfy the given
467 * predicate. Errors or runtime exceptions thrown during iteration or by
468 * the predicate are relayed to the caller.
469 *
470 * @implSpec
471 * The default implementation traverses all elements of the collection using
472 * its {@link #iterator}. Each matching element is removed using
473 * {@link Iterator#remove()}. If the collection's iterator does not
474 * support removal then an {@code UnsupportedOperationException} will be
475 * thrown on the first matching element.
476 *
477 * @param filter a predicate which returns {@code true} for elements to be
478 * removed
479 * @return {@code true} if any elements were removed
480 * @throws NullPointerException if the specified filter is null
481 * @throws UnsupportedOperationException if elements cannot be removed
482 * from this collection. Implementations may throw this exception if a
483 * matching element cannot be removed or if, in general, removal is not
484 * supported.
485 * @since 1.8
486 */
487 default boolean removeIf(Predicate<? super E> filter) {
488 Objects.requireNonNull(filter);
489 boolean removed = false;
490 final Iterator<E> each = iterator();
491 while (each.hasNext()) {
492 if (filter.test(each.next())) {
493 each.remove();
494 removed = true;
495 }
496 }
497 return removed;
498 }
499
500 /**
501 * Retains only the elements in this collection that are contained in the
502 * specified collection (optional operation). In other words, removes from
503 * this collection all of its elements that are not contained in the
504 * specified collection.
505 *
506 * @param c collection containing elements to be retained in this collection
507 * @return {@code true} if this collection changed as a result of the call
508 * @throws UnsupportedOperationException if the {@code retainAll} operation
509 * is not supported by this collection
510 * @throws ClassCastException if the types of one or more elements
511 * in this collection are incompatible with the specified
512 * collection
513 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
514 * @throws NullPointerException if this collection contains one or more
515 * null elements and the specified collection does not permit null
516 * elements
517 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>),
518 * or if the specified collection is null
519 * @see #remove(Object)
520 * @see #contains(Object)
521 */
522 boolean retainAll(Collection<?> c);
523
524 /**
525 * Removes all of the elements from this collection (optional operation).
526 * The collection will be empty after this method returns.
527 *
528 * @throws UnsupportedOperationException if the {@code clear} operation
529 * is not supported by this collection
530 */
531 void clear();
532
533
534 // Comparison and hashing
535
536 /**
537 * Compares the specified object with this collection for equality. <p>
538 *
539 * While the {@code Collection} interface adds no stipulations to the
540 * general contract for the {@code Object.equals}, programmers who
541 * implement the {@code Collection} interface "directly" (in other words,
542 * create a class that is a {@code Collection} but is not a {@code Set}
543 * or a {@code List}) must exercise care if they choose to override the
544 * {@code Object.equals}. It is not necessary to do so, and the simplest
545 * course of action is to rely on {@code Object}'s implementation, but
546 * the implementor may wish to implement a "value comparison" in place of
547 * the default "reference comparison." (The {@code List} and
548 * {@code Set} interfaces mandate such value comparisons.)<p>
549 *
550 * The general contract for the {@code Object.equals} method states that
551 * equals must be symmetric (in other words, {@code a.equals(b)} if and
552 * only if {@code b.equals(a)}). The contracts for {@code List.equals}
553 * and {@code Set.equals} state that lists are only equal to other lists,
554 * and sets to other sets. Thus, a custom {@code equals} method for a
555 * collection class that implements neither the {@code List} nor
556 * {@code Set} interface must return {@code false} when this collection
557 * is compared to any list or set. (By the same logic, it is not possible
558 * to write a class that correctly implements both the {@code Set} and
559 * {@code List} interfaces.)
560 *
561 * @param o object to be compared for equality with this collection
562 * @return {@code true} if the specified object is equal to this
563 * collection
564 *
565 * @see Object#equals(Object)
566 * @see Set#equals(Object)
567 * @see List#equals(Object)
568 */
569 boolean equals(Object o);
570
571 /**
572 * Returns the hash code value for this collection. While the
573 * {@code Collection} interface adds no stipulations to the general
574 * contract for the {@code Object.hashCode} method, programmers should
575 * take note that any class that overrides the {@code Object.equals}
576 * method must also override the {@code Object.hashCode} method in order
577 * to satisfy the general contract for the {@code Object.hashCode} method.
578 * In particular, {@code c1.equals(c2)} implies that
579 * {@code c1.hashCode()==c2.hashCode()}.
580 *
581 * @return the hash code value for this collection
582 *
583 * @see Object#hashCode()
584 * @see Object#equals(Object)
585 */
586 int hashCode();
587
588 /**
589 * Creates a {@link Spliterator} over the elements in this collection.
590 *
591 * Implementations should document characteristic values reported by the
592 * spliterator. Such characteristic values are not required to be reported
593 * if the spliterator reports {@link Spliterator#SIZED} and this collection
594 * contains no elements.
595 *
596 * <p>The default implementation should be overridden by subclasses that
597 * can return a more efficient spliterator. In order to
598 * preserve expected laziness behavior for the {@link #stream()} and
599 * {@link #parallelStream()} methods, spliterators should either have the
600 * characteristic of {@code IMMUTABLE} or {@code CONCURRENT}, or be
601 * <em><a href="Spliterator.html#binding">late-binding</a></em>.
602 * If none of these is practical, the overriding class should describe the
603 * spliterator's documented policy of binding and structural interference,
604 * and should override the {@link #stream()} and {@link #parallelStream()}
605 * methods to create streams using a {@code Supplier} of the spliterator,
606 * as in:
607 * <pre>{@code
608 * Stream<E> s = StreamSupport.stream(() -> spliterator(), spliteratorCharacteristics)
609 * }</pre>
610 * <p>These requirements ensure that streams produced by the
611 * {@link #stream()} and {@link #parallelStream()} methods will reflect the
612 * contents of the collection as of initiation of the terminal stream
613 * operation.
614 *
615 * @implSpec
616 * The default implementation creates a
617 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
618 * from the collection's {@code Iterator}. The spliterator inherits the
619 * <em>fail-fast</em> properties of the collection's iterator.
620 * <p>
621 * The created {@code Spliterator} reports {@link Spliterator#SIZED}.
622 *
623 * @implNote
624 * The created {@code Spliterator} additionally reports
625 * {@link Spliterator#SUBSIZED}.
626 *
627 * <p>If a spliterator covers no elements then the reporting of additional
628 * characteristic values, beyond that of {@code SIZED} and {@code SUBSIZED},
629 * does not aid clients to control, specialize or simplify computation.
630 * However, this does enable shared use of an immutable and empty
631 * spliterator instance (see {@link Spliterators#emptySpliterator()}) for
632 * empty collections, and enables clients to determine if such a spliterator
633 * covers no elements.
634 *
635 * @return a {@code Spliterator} over the elements in this collection
636 * @since 1.8
637 */
638 @Override
639 default Spliterator<E> spliterator() {
640 return Spliterators.spliterator(this, 0);
641 }
642
643 /**
644 * Returns a sequential {@code Stream} with this collection as its source.
645 *
646 * <p>This method should be overridden when the {@link #spliterator()}
647 * method cannot return a spliterator that is {@code IMMUTABLE},
648 * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
649 * for details.)
650 *
651 * @implSpec
652 * The default implementation creates a sequential {@code Stream} from the
653 * collection's {@code Spliterator}.
654 *
655 * @return a sequential {@code Stream} over the elements in this collection
656 * @since 1.8
657 */
658 default Stream<E> stream() {
659 return StreamSupport.stream(spliterator(), false);
660 }
661
662 /**
663 * Returns a possibly parallel {@code Stream} with this collection as its
664 * source. It is allowable for this method to return a sequential stream.
665 *
666 * <p>This method should be overridden when the {@link #spliterator()}
667 * method cannot return a spliterator that is {@code IMMUTABLE},
668 * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
669 * for details.)
670 *
671 * @implSpec
672 * The default implementation creates a parallel {@code Stream} from the
673 * collection's {@code Spliterator}.
674 *
675 * @return a possibly parallel {@code Stream} over the elements in this
676 * collection
677 * @since 1.8
678 */
679 default Stream<E> parallelStream() {
680 return StreamSupport.stream(spliterator(), true);
681 }
682 }