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
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  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 <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<E> extends 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&nbsp;?&nbsp;e==null&nbsp;:&nbsp;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     /**
 182      * Returns an iterator over the elements in this collection.  There are no
 183      * guarantees concerning the order in which the elements are returned
 184      * (unless this collection is an instance of some class that provides a
 185      * guarantee).
 186      *
 187      * @return an <tt>Iterator</tt> over the elements in this collection
 188      */
 189     Iterator<E> iterator();
 190 
 191     /**
 192      * Returns an array containing all of the elements in this collection.
 193      * If this collection makes any guarantees as to what order its elements
 194      * are returned by its iterator, this method must return the elements in
 195      * the same order.
 196      *
 197      * <p>The returned array will be "safe" in that no references to it are
 198      * maintained by this collection.  (In other words, this method must
 199      * allocate a new array even if this collection is backed by an array).
 200      * The caller is thus free to modify the returned array.
 201      *
 202      * <p>This method acts as bridge between array-based and collection-based
 203      * APIs.
 204      *
 205      * @return an array containing all of the elements in this collection
 206      */
 207     Object[] toArray();
 208 
 209     /**
 210      * Returns an array containing all of the elements in this collection;
 211      * the runtime type of the returned array is that of the specified array.
 212      * If the collection fits in the specified array, it is returned therein.
 213      * Otherwise, a new array is allocated with the runtime type of the
 214      * specified array and the size of this collection.
 215      *
 216      * <p>If this collection fits in the specified array with room to spare
 217      * (i.e., the array has more elements than this collection), the element
 218      * in the array immediately following the end of the collection is set to
 219      * <tt>null</tt>.  (This is useful in determining the length of this
 220      * collection <i>only</i> if the caller knows that this collection does
 221      * not contain any <tt>null</tt> elements.)
 222      *
 223      * <p>If this collection makes any guarantees as to what order its elements
 224      * are returned by its iterator, this method must return the elements in
 225      * the same order.
 226      *
 227      * <p>Like the {@link #toArray()} method, this method acts as bridge between
 228      * array-based and collection-based APIs.  Further, this method allows
 229      * precise control over the runtime type of the output array, and may,
 230      * under certain circumstances, be used to save allocation costs.
 231      *
 232      * <p>Suppose <tt>x</tt> is a collection known to contain only strings.
 233      * The following code can be used to dump the collection into a newly
 234      * allocated array of <tt>String</tt>:
 235      *
 236      * <pre>
 237      *     String[] y = x.toArray(new String[0]);</pre>
 238      *
 239      * Note that <tt>toArray(new Object[0])</tt> is identical in function to
 240      * <tt>toArray()</tt>.
 241      *
 242      * @param <T> the runtime type of the array to contain the collection
 243      * @param a the array into which the elements of this collection are to be
 244      *        stored, if it is big enough; otherwise, a new array of the same
 245      *        runtime type is allocated for this purpose.
 246      * @return an array containing all of the elements in this collection
 247      * @throws ArrayStoreException if the runtime type of the specified array
 248      *         is not a supertype of the runtime type of every element in
 249      *         this collection
 250      * @throws NullPointerException if the specified array is null
 251      */
 252     <T> T[] toArray(T[] a);
 253 
 254     // Modification Operations
 255 
 256     /**
 257      * Ensures that this collection contains the specified element (optional
 258      * operation).  Returns <tt>true</tt> if this collection changed as a
 259      * result of the call.  (Returns <tt>false</tt> if this collection does
 260      * not permit duplicates and already contains the specified element.)<p>
 261      *
 262      * Collections that support this operation may place limitations on what
 263      * elements may be added to this collection.  In particular, some
 264      * collections will refuse to add <tt>null</tt> elements, and others will
 265      * impose restrictions on the type of elements that may be added.
 266      * Collection classes should clearly specify in their documentation any
 267      * restrictions on what elements may be added.<p>
 268      *
 269      * If a collection refuses to add a particular element for any reason
 270      * other than that it already contains the element, it <i>must</i> throw
 271      * an exception (rather than returning <tt>false</tt>).  This preserves
 272      * the invariant that a collection always contains the specified element
 273      * after this call returns.
 274      *
 275      * @param e element whose presence in this collection is to be ensured
 276      * @return <tt>true</tt> if this collection changed as a result of the
 277      *         call
 278      * @throws UnsupportedOperationException if the <tt>add</tt> operation
 279      *         is not supported by this collection
 280      * @throws ClassCastException if the class of the specified element
 281      *         prevents it from being added to this collection
 282      * @throws NullPointerException if the specified element is null and this
 283      *         collection does not permit null elements
 284      * @throws IllegalArgumentException if some property of the element
 285      *         prevents it from being added to this collection
 286      * @throws IllegalStateException if the element cannot be added at this
 287      *         time due to insertion restrictions
 288      */
 289     boolean add(E e);
 290 
 291     /**
 292      * Removes a single instance of the specified element from this
 293      * collection, if it is present (optional operation).  More formally,
 294      * removes an element <tt>e</tt> such that
 295      * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>, if
 296      * this collection contains one or more such elements.  Returns
 297      * <tt>true</tt> if this collection contained the specified element (or
 298      * equivalently, if this collection changed as a result of the call).
 299      *
 300      * @param o element to be removed from this collection, if present
 301      * @return <tt>true</tt> if an element was removed as a result of this call
 302      * @throws ClassCastException if the type of the specified element
 303      *         is incompatible with this collection
 304      *         (<a href="#optional-restrictions">optional</a>)
 305      * @throws NullPointerException if the specified element is null and this
 306      *         collection does not permit null elements
 307      *         (<a href="#optional-restrictions">optional</a>)
 308      * @throws UnsupportedOperationException if the <tt>remove</tt> operation
 309      *         is not supported by this collection
 310      */
 311     boolean remove(Object o);
 312 










 313 
 314     // Bulk Operations
 315 
 316     /**
 317      * Returns <tt>true</tt> if this collection contains all of the elements
 318      * in the specified collection.
 319      *
 320      * @param  c collection to be checked for containment in this collection
 321      * @return <tt>true</tt> if this collection contains all of the elements
 322      *         in the specified collection
 323      * @throws ClassCastException if the types of one or more elements
 324      *         in the specified collection are incompatible with this
 325      *         collection
 326      *         (<a href="#optional-restrictions">optional</a>)
 327      * @throws NullPointerException if the specified collection contains one
 328      *         or more null elements and this collection does not permit null
 329      *         elements
 330      *         (<a href="#optional-restrictions">optional</a>),
 331      *         or if the specified collection is null.
 332      * @see    #contains(Object)
 333      */
 334     boolean containsAll(Collection<?> c);
 335 










 336     /**
 337      * Adds all of the elements in the specified collection to this collection
 338      * (optional operation).  The behavior of this operation is undefined if
 339      * the specified collection is modified while the operation is in progress.
 340      * (This implies that the behavior of this call is undefined if the
 341      * specified collection is this collection, and this collection is
 342      * nonempty.)
 343      *
 344      * @param c collection containing elements to be added to this collection
 345      * @return <tt>true</tt> if this collection changed as a result of the call
 346      * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
 347      *         is not supported by this collection
 348      * @throws ClassCastException if the class of an element of the specified
 349      *         collection prevents it from being added to this collection
 350      * @throws NullPointerException if the specified collection contains a
 351      *         null element and this collection does not permit null elements,
 352      *         or if the specified collection is null
 353      * @throws IllegalArgumentException if some property of an element of the
 354      *         specified collection prevents it from being added to this
 355      *         collection
 356      * @throws IllegalStateException if not all the elements can be added at
 357      *         this time due to insertion restrictions
 358      * @see #add(Object)
 359      */
 360     boolean addAll(Collection<? extends E> c);
 361 
 362     /**
 363      * Removes all of this collection's elements that are also contained in the
 364      * specified collection (optional operation).  After this call returns,
 365      * this collection will contain no elements in common with the specified
 366      * collection.
 367      *
 368      * @param c collection containing elements to be removed from this collection
 369      * @return <tt>true</tt> if this collection changed as a result of the
 370      *         call
 371      * @throws UnsupportedOperationException if the <tt>removeAll</tt> method
 372      *         is not supported by this collection
 373      * @throws ClassCastException if the types of one or more elements
 374      *         in this collection are incompatible with the specified
 375      *         collection
 376      *         (<a href="#optional-restrictions">optional</a>)
 377      * @throws NullPointerException if this collection contains one or more
 378      *         null elements and the specified collection does not support
 379      *         null elements
 380      *         (<a href="#optional-restrictions">optional</a>),
 381      *         or if the specified collection is null
 382      * @see #remove(Object)
 383      * @see #contains(Object)
 384      */
 385     boolean removeAll(Collection<?> c);
 386 













 387     /**
 388      * Removes all of the elements of this collection that satisfy the given
 389      * predicate.  Errors or runtime exceptions thrown during iteration or by
 390      * the predicate are relayed to the caller.
 391      *
 392      * @implSpec
 393      * The default implementation traverses all elements of the collection using
 394      * its {@link #iterator}.  Each matching element is removed using
 395      * {@link Iterator#remove()}.  If the collection's iterator does not
 396      * support removal then an {@code UnsupportedOperationException} will be
 397      * thrown on the first matching element.
 398      *
 399      * @param filter a predicate which returns {@code true} for elements to be
 400      *        removed
 401      * @return {@code true} if any elements were removed
 402      * @throws NullPointerException if the specified filter is null
 403      * @throws UnsupportedOperationException if elements cannot be removed
 404      *         from this collection.  Implementations may throw this exception if a
 405      *         matching element cannot be removed or if, in general, removal is not
 406      *         supported.
 407      * @since 1.8
 408      */
 409     default boolean removeIf(Predicate<? super E> filter) {
 410         Objects.requireNonNull(filter);
 411         boolean removed = false;
 412         final Iterator<E> each = iterator();
 413         while (each.hasNext()) {
 414             if (filter.test(each.next())) {
 415                 each.remove();
 416                 removed = true;
 417             }
 418         }
 419         return removed;
 420     }
 421 
 422     /**
 423      * Retains only the elements in this collection that are contained in the
 424      * specified collection (optional operation).  In other words, removes from
 425      * this collection all of its elements that are not contained in the
 426      * specified collection.
 427      *
 428      * @param c collection containing elements to be retained in this collection
 429      * @return <tt>true</tt> if this collection changed as a result of the call
 430      * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
 431      *         is not supported by this collection
 432      * @throws ClassCastException if the types of one or more elements
 433      *         in this collection are incompatible with the specified
 434      *         collection
 435      *         (<a href="#optional-restrictions">optional</a>)
 436      * @throws NullPointerException if this collection contains one or more
 437      *         null elements and the specified collection does not permit null
 438      *         elements
 439      *         (<a href="#optional-restrictions">optional</a>),
 440      *         or if the specified collection is null
 441      * @see #remove(Object)
 442      * @see #contains(Object)
 443      */
 444     boolean retainAll(Collection<?> c);
 445 













 446     /**
 447      * Removes all of the elements from this collection (optional operation).
 448      * The collection will be empty after this method returns.
 449      *
 450      * @throws UnsupportedOperationException if the <tt>clear</tt> operation
 451      *         is not supported by this collection
 452      */
 453     void clear();
 454 
 455 
 456     // Comparison and hashing
 457 
 458     /**
 459      * Compares the specified object with this collection for equality. <p>
 460      *
 461      * While the <tt>Collection</tt> interface adds no stipulations to the
 462      * general contract for the <tt>Object.equals</tt>, programmers who
 463      * implement the <tt>Collection</tt> interface "directly" (in other words,
 464      * create a class that is a <tt>Collection</tt> but is not a <tt>Set</tt>
 465      * or a <tt>List</tt>) must exercise care if they choose to override the
 466      * <tt>Object.equals</tt>.  It is not necessary to do so, and the simplest
 467      * course of action is to rely on <tt>Object</tt>'s implementation, but
 468      * the implementor may wish to implement a "value comparison" in place of
 469      * the default "reference comparison."  (The <tt>List</tt> and
 470      * <tt>Set</tt> interfaces mandate such value comparisons.)<p>
 471      *
 472      * The general contract for the <tt>Object.equals</tt> method states that
 473      * equals must be symmetric (in other words, <tt>a.equals(b)</tt> if and
 474      * only if <tt>b.equals(a)</tt>).  The contracts for <tt>List.equals</tt>
 475      * and <tt>Set.equals</tt> state that lists are only equal to other lists,
 476      * and sets to other sets.  Thus, a custom <tt>equals</tt> method for a
 477      * collection class that implements neither the <tt>List</tt> nor
 478      * <tt>Set</tt> interface must return <tt>false</tt> when this collection
 479      * is compared to any list or set.  (By the same logic, it is not possible
 480      * to write a class that correctly implements both the <tt>Set</tt> and
 481      * <tt>List</tt> interfaces.)
 482      *
 483      * @param o object to be compared for equality with this collection
 484      * @return <tt>true</tt> if the specified object is equal to this
 485      * collection
 486      *
 487      * @see Object#equals(Object)
 488      * @see Set#equals(Object)
 489      * @see List#equals(Object)
 490      */
 491     boolean equals(Object o);
 492 
 493     /**
 494      * Returns the hash code value for this collection.  While the
 495      * <tt>Collection</tt> interface adds no stipulations to the general
 496      * contract for the <tt>Object.hashCode</tt> method, programmers should
 497      * take note that any class that overrides the <tt>Object.equals</tt>
 498      * method must also override the <tt>Object.hashCode</tt> method in order
 499      * to satisfy the general contract for the <tt>Object.hashCode</tt> method.
 500      * In particular, <tt>c1.equals(c2)</tt> implies that
 501      * <tt>c1.hashCode()==c2.hashCode()</tt>.
 502      *
 503      * @return the hash code value for this collection
 504      *
 505      * @see Object#hashCode()
 506      * @see Object#equals(Object)
 507      */
 508     int hashCode();
 509 
 510     /**
 511      * Creates a {@link Spliterator} over the elements in this collection.
 512      *
 513      * Implementations should document characteristic values reported by the
 514      * spliterator.  Such characteristic values are not required to be reported
 515      * if the spliterator reports {@link Spliterator#SIZED} and this collection
 516      * contains no elements.
 517      *
 518      * <p>The default implementation should be overridden by subclasses that
 519      * can return a more efficient spliterator.  In order to
 520      * preserve expected laziness behavior for the {@link #stream()} and
 521      * {@link #parallelStream()} methods, spliterators should either have the
 522      * characteristic of {@code IMMUTABLE} or {@code CONCURRENT}, or be
 523      * <em><a href="Spliterator.html#binding">late-binding</a></em>.
 524      * If none of these is practical, the overriding class should describe the
 525      * spliterator's documented policy of binding and structural interference,
 526      * and should override the {@link #stream()} and {@link #parallelStream()}
 527      * methods to create streams using a {@code Supplier} of the spliterator,
 528      * as in:
 529      * <pre>{@code
 530      *     Stream<E> s = StreamSupport.stream(() -> spliterator(), spliteratorCharacteristics)
 531      * }</pre>
 532      * <p>These requirements ensure that streams produced by the
 533      * {@link #stream()} and {@link #parallelStream()} methods will reflect the
 534      * contents of the collection as of initiation of the terminal stream
 535      * operation.
 536      *
 537      * @implSpec
 538      * The default implementation creates a
 539      * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
 540      * from the collections's {@code Iterator}.  The spliterator inherits the
 541      * <em>fail-fast</em> properties of the collection's iterator.
 542      * <p>
 543      * The created {@code Spliterator} reports {@link Spliterator#SIZED}.
 544      *
 545      * @implNote
 546      * The created {@code Spliterator} additionally reports
 547      * {@link Spliterator#SUBSIZED}.
 548      *
 549      * <p>If a spliterator covers no elements then the reporting of additional
 550      * characteristic values, beyond that of {@code SIZED} and {@code SUBSIZED},
 551      * does not aid clients to control, specialize or simplify computation.
 552      * However, this does enable shared use of an immutable and empty
 553      * spliterator instance (see {@link Spliterators#emptySpliterator()}) for
 554      * empty collections, and enables clients to determine if such a spliterator
 555      * covers no elements.
 556      *
 557      * @return a {@code Spliterator} over the elements in this collection
 558      * @since 1.8
 559      */
 560     @Override
 561     default Spliterator<E> spliterator() {
 562         return Spliterators.spliterator(this, 0);
 563     }
 564 
 565     /**
 566      * Returns a sequential {@code Stream} with this collection as its source.
 567      *
 568      * <p>This method should be overridden when the {@link #spliterator()}
 569      * method cannot return a spliterator that is {@code IMMUTABLE},
 570      * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
 571      * for details.)
 572      *
 573      * @implSpec
 574      * The default implementation creates a sequential {@code Stream} from the
 575      * collection's {@code Spliterator}.
 576      *
 577      * @return a sequential {@code Stream} over the elements in this collection
 578      * @since 1.8
 579      */
 580     default Stream<E> stream() {
 581         return StreamSupport.stream(spliterator(), false);
 582     }
 583 
 584     /**
 585      * Returns a possibly parallel {@code Stream} with this collection as its
 586      * source.  It is allowable for this method to return a sequential stream.
 587      *
 588      * <p>This method should be overridden when the {@link #spliterator()}
 589      * method cannot return a spliterator that is {@code IMMUTABLE},
 590      * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
 591      * for details.)
 592      *
 593      * @implSpec
 594      * The default implementation creates a parallel {@code Stream} from the
 595      * collection's {@code Spliterator}.
 596      *
 597      * @return a possibly parallel {@code Stream} over the elements in this
 598      * collection
 599      * @since 1.8
 600      */
 601     default Stream<E> parallelStream() {
 602         return StreamSupport.stream(spliterator(), true);
 603     }
 604 }
--- EOF ---