/*
 * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.util;

import java.util.function.IntFunction;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * The root interface in the <i>collection hierarchy</i>. A collection
 * represents a group of objects, known as its <i>elements</i>. Some
 * collections allow duplicate elements and others do not. Some are ordered
 * and others unordered. The JDK does not provide any <i>direct</i>
 * implementations of this interface: it provides implementations of more
 * specific subinterfaces like {@code Set} and {@code List}. This interface
 * is typically used to pass collections around and manipulate them where
 * maximum generality is desired.
 *
 * <p><i>Bags</i> or <i>multisets</i> (unordered collections that may contain
 * duplicate elements) should implement this interface directly.
 *
 * <p>All general-purpose {@code Collection} implementation classes (which
 * typically implement {@code Collection} indirectly through one of its
 * subinterfaces) should provide two "standard" constructors: a void (no
 * arguments) constructor, which creates an empty collection, and a
 * constructor with a single argument of type {@code Collection}, which
 * creates a new collection with the same elements as its argument. In
 * effect, the latter constructor allows the user to copy any collection,
 * producing an equivalent collection of the desired implementation type.
 * There is no way to enforce this convention (as interfaces cannot contain
 * constructors) but all of the general-purpose {@code Collection}
 * implementations in the Java platform libraries comply.
 *
 * <p>Certain methods are specified to be
 * <i>optional</i>. If a collection implementation doesn't implement a
 * particular operation, it should define the corresponding method to throw
 * {@code UnsupportedOperationException}. Such methods are marked "optional
 * operation" in method specifications of the collections interfaces.
 *
 * <p><a id="optional-restrictions"></a>Some collection implementations
 * have restrictions on the elements that they may contain.
 * For example, some implementations prohibit null elements,
 * and some have restrictions on the types of their elements. Attempting to
 * add an ineligible element throws an unchecked exception, typically
 * {@code NullPointerException} or {@code ClassCastException}. Attempting
 * to query the presence of an ineligible element may throw an exception,
 * or it may simply return false; some implementations will exhibit the former
 * behavior and some will exhibit the latter. More generally, attempting an
 * operation on an ineligible element whose completion would not result in
 * the insertion of an ineligible element into the collection may throw an
 * exception or it may succeed, at the option of the implementation.
 * Such exceptions are marked as "optional" in the specification for this
 * interface.
 *
 * <p>It is up to each collection to determine its own synchronization
 * policy. In the absence of a stronger guarantee by the
 * implementation, undefined behavior may result from the invocation
 * of any method on a collection that is being mutated by another
 * thread; this includes direct invocations, passing the collection to
 * a method that might perform invocations, and using an existing
 * iterator to examine the collection.
 *
 * <p>Many methods in Collections Framework interfaces are defined in
 * terms of the {@link Object#equals(Object) equals} method. For example,
 * the specification for the {@link #contains(Object) contains(Object o)}
 * method says: "returns {@code true} if and only if this collection
 * contains at least one element {@code e} such that
 * {@code (o==null ? e==null : o.equals(e))}." This specification should
 * <i>not</i> be construed to imply that invoking {@code Collection.contains}
 * with a non-null argument {@code o} will cause {@code o.equals(e)} to be
 * invoked for any element {@code e}. Implementations are free to implement
 * optimizations whereby the {@code equals} invocation is avoided, for
 * example, by first comparing the hash codes of the two elements. (The
 * {@link Object#hashCode()} specification guarantees that two objects with
 * unequal hash codes cannot be equal.) More generally, implementations of
 * the various Collections Framework interfaces are free to take advantage of
 * the specified behavior of underlying {@link Object} methods wherever the
 * implementor deems it appropriate.
 *
 * <p>Some collection operations which perform recursive traversal of the
 * collection may fail with an exception for self-referential instances where
 * the collection directly or indirectly contains itself. This includes the
 * {@code clone()}, {@code equals()}, {@code hashCode()} and {@code toString()}
 * methods. Implementations may optionally handle the self-referential scenario,
 * however most current implementations do not do so.
 *
 * <h2><a id="view">View Collections</a></h2>
 *
 * <p>Most collections manage storage for elements they contain. By contrast, <i>view
 * collections</i> themselves do not store elements, but instead they rely on a
 * backing collection to store the actual elements. Operations that are not handled
 * by the view collection itself are delegated to the backing collection. Examples of
 * view collections include the wrapper collections returned by methods such as
 * {@link Collections#checkedCollection Collections.checkedCollection},
 * {@link Collections#synchronizedCollection Collections.synchronizedCollection}, and
 * {@link Collections#unmodifiableCollection Collections.unmodifiableCollection}.
 * Other examples of view collections include collections that provide a
 * different representation of the same elements, for example, as
 * provided by {@link List#subList List.subList},
 * {@link NavigableSet#subSet NavigableSet.subSet}, or
 * {@link Map#entrySet Map.entrySet}.
 * Any changes made to the backing collection are visible in the view collection.
 * Correspondingly, any changes made to the view collection &mdash; if changes
 * are permitted &mdash; are written through to the backing collection.
 * Although they technically aren't collections, instances of
 * {@link Iterator} and {@link ListIterator} can also allow modifications
 * to be written through to the backing collection, and in some cases,
 * modifications to the backing collection will be visible to the Iterator
 * during iteration.
 *
 * <h2><a id="unmodifiable">Unmodifiable Collections</a></h2>
 *
 * <p>Certain methods of this interface are considered "destructive" and are called
 * "mutator" methods in that they modify the group of objects contained within
 * the collection on which they operate. They can be specified to throw
 * {@code UnsupportedOperationException} if this collection implementation
 * does not support the operation. Such methods should (but are not required
 * to) throw an {@code UnsupportedOperationException} if the invocation would
 * have no effect on the collection. For example, consider a collection that
 * does not support the {@link #add add} operation. What will happen if the
 * {@link #addAll addAll} method is invoked on this collection, with an empty
 * collection as the argument? The addition of zero elements has no effect,
 * so it is permissible for this collection simply to do nothing and not to throw
 * an exception. However, it is recommended that such cases throw an exception
 * unconditionally, as throwing only in certain cases can lead to
 * programming errors.
 *
 * <p>An <i>unmodifiable collection</i> is a collection, all of whose
 * mutator methods (as defined above) are specified to throw
 * {@code UnsupportedOperationException}. Such a collection thus cannot be
 * modified by calling any methods on it. For a collection to be properly
 * unmodifiable, any view collections derived from it must also be unmodifiable.
 * For example, if a List is unmodifiable, the List returned by
 * {@link List#subList List.subList} is also unmodifiable.
 *
 * <p>An unmodifiable collection is not necessarily immutable. If the
 * contained elements are mutable, the entire collection is clearly
 * mutable, even though it might be unmodifiable. For example, consider
 * two unmodifiable lists containing mutable elements. The result of calling
 * {@code list1.equals(list2)} might differ from one call to the next if
 * the elements had been mutated, even though both lists are unmodifiable.
 * However, if an unmodifiable collection contains all immutable elements,
 * it can be considered effectively immutable.
 *
 * <h2><a id="unmodview">Unmodifiable View Collections</a></h2>
 *
 * <p>An <i>unmodifiable view collection</i> is a collection that is unmodifiable
 * and that is also a view onto a backing collection. Its mutator methods throw
 * {@code UnsupportedOperationException}, as described above, while
 * reading and querying methods are delegated to the backing collection.
 * The effect is to provide read-only access to the backing collection.
 * This is useful for a component to provide users with read access to
 * an internal collection, while preventing them from modifying such
 * collections unexpectedly. Examples of unmodifiable view collections
 * are those returned by the
 * {@link Collections#unmodifiableCollection Collections.unmodifiableCollection},
 * {@link Collections#unmodifiableList Collections.unmodifiableList}, and
 * related methods.
 *
 * <p>Note that changes to the backing collection might still be possible,
 * and if they occur, they are visible through the unmodifiable view. Thus,
 * an unmodifiable view collection is not necessarily immutable. However,
 * if the backing collection of an unmodifiable view is effectively immutable,
 * or if the only reference to the backing collection is through an
 * unmodifiable view, the view can be considered effectively immutable.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @implSpec
 * The default method implementations (inherited or otherwise) do not apply any
 * synchronization protocol. If a {@code Collection} implementation has a
 * specific synchronization protocol, then it must override default
 * implementations to apply that protocol.
 *
 * @param <E> the type of elements in this collection
 *
 * @author Josh Bloch
 * @author Neal Gafter
 * @see Set
 * @see List
 * @see Map
 * @see SortedSet
 * @see SortedMap
 * @see HashSet
 * @see TreeSet
 * @see ArrayList
 * @see LinkedList
 * @see Vector
 * @see Collections
 * @see Arrays
 * @see AbstractCollection
 * @since 1.2
 */

public interface Collection<E> extends Iterable<E> {
 // Query Operations

 /**
 * Returns the number of elements in this collection. If this collection
 * contains more than {@code Integer.MAX_VALUE} elements, returns
 * {@code Integer.MAX_VALUE}.
 *
 * @return the number of elements in this collection
 */
 int size();

 /**
 * Returns {@code true} if this collection contains no elements.
 *
 * @return {@code true} if this collection contains no elements
 */
 boolean isEmpty();

 /**
 * Returns {@code true} if this collection contains the specified element.
 * More formally, returns {@code true} if and only if this collection
 * contains at least one element {@code e} such that
 * {@code Objects.equals(o, e)}.
 *
 * @param o element whose presence in this collection is to be tested
 * @return {@code true} if this collection contains the specified
 * element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this collection
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * collection does not permit null elements
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 */
 boolean contains(Object o);

 /**
 * Returns an iterator over the elements in this collection. There are no
 * guarantees concerning the order in which the elements are returned
 * (unless this collection is an instance of some class that provides a
 * guarantee).
 *
 * @return an {@code Iterator} over the elements in this collection
 */
 Iterator<E> iterator();

 /**
 * Returns an array containing all of the elements in this collection.
 * If this collection makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the elements in
 * the same order. The returned array's {@linkplain Class#getComponentType
 * runtime component type} is {@code Object}.
 *
 * <p>The returned array will be "safe" in that no references to it are
 * maintained by this collection. (In other words, this method must
 * allocate a new array even if this collection is backed by an array).
 * The caller is thus free to modify the returned array.
 *
 * @apiNote
 * This method acts as a bridge between array-based and collection-based APIs.
 * It returns an array whose runtime type is {@code Object[]}.
 * Use {@link #toArray(Object[]) toArray(T[])} to reuse an existing
 * array, or use {@link #toArray(IntFunction)} to control the runtime type
 * of the array.
 *
 * @return an array, whose {@linkplain Class#getComponentType runtime component
 * type} is {@code Object}, containing all of the elements in this collection
 */
 Object[] toArray();

 /**
 * Returns an array containing all of the elements in this collection;
 * the runtime type of the returned array is that of the specified array.
 * If the collection fits in the specified array, it is returned therein.
 * Otherwise, a new array is allocated with the runtime type of the
 * specified array and the size of this collection.
 *
 * <p>If this collection fits in the specified array with room to spare
 * (i.e., the array has more elements than this collection), the element
 * in the array immediately following the end of the collection is set to
 * {@code null}. (This is useful in determining the length of this
 * collection <i>only</i> if the caller knows that this collection does
 * not contain any {@code null} elements.)
 *
 * <p>If this collection makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the elements in
 * the same order.
 *
 * @apiNote
 * This method acts as a bridge between array-based and collection-based APIs.
 * It allows an existing array to be reused under certain circumstances.
 * Use {@link #toArray()} to create an array whose runtime type is {@code Object[]},
 * or use {@link #toArray(IntFunction)} to control the runtime type of
 * the array.
 *
 * <p>Suppose {@code x} is a collection known to contain only strings.
 * The following code can be used to dump the collection into a previously
 * allocated {@code String} array:
 *
 * <pre>
 * String[] y = new String[SIZE];
 * ...
 * y = x.toArray(y);</pre>
 *
 * <p>The return value is reassigned to the variable {@code y}, because a
 * new array will be allocated and returned if the collection {@code x} has
 * too many elements to fit into the existing array {@code y}.
 *
 * <p>Note that {@code toArray(new Object[0])} is identical in function to
 * {@code toArray()}.
 *
 * @param <T> the component type of the array to contain the collection
 * @param a the array into which the elements of this collection are to be
 * stored, if it is big enough; otherwise, a new array of the same
 * runtime type is allocated for this purpose.
 * @return an array containing all of the elements in this collection
 * @throws ArrayStoreException if the runtime type of any element in this
 * collection is not assignable to the {@linkplain Class#getComponentType
 * runtime component type} of the specified array
 * @throws NullPointerException if the specified array is null
 */
 <T> T[] toArray(T[] a);

 /**
 * Returns an array containing all of the elements in this collection,
 * using the provided {@code generator} function to allocate the returned array.
 *
 * <p>If this collection makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the elements in
 * the same order.
 *
 * @apiNote
 * This method acts as a bridge between array-based and collection-based APIs.
 * It allows creation of an array of a particular runtime type. Use
 * {@link #toArray()} to create an array whose runtime type is {@code Object[]},
 * or use {@link #toArray(Object[]) toArray(T[])} to reuse an existing array.
 *
 * <p>Suppose {@code x} is a collection known to contain only strings.
 * The following code can be used to dump the collection into a newly
 * allocated array of {@code String}:
 *
 * <pre>
 * String[] y = x.toArray(String[]::new);</pre>
 *
 * @implSpec
 * The default implementation calls the generator function with zero
 * and then passes the resulting array to {@link #toArray(Object[]) toArray(T[])}.
 *
 * @param <T> the component type of the array to contain the collection
 * @param generator a function which produces a new array of the desired
 * type and the provided length
 * @return an array containing all of the elements in this collection
 * @throws ArrayStoreException if the runtime type of any element in this
 * collection is not assignable to the {@linkplain Class#getComponentType
 * runtime component type} of the generated array
 * @throws NullPointerException if the generator function is null
 * @since 11
 */
 default <T> T[] toArray(IntFunction<T[]> generator) {
 return toArray(generator.apply(0));
 }

 // Modification Operations

 /**
 * Ensures that this collection contains the specified element (optional
 * operation). Returns {@code true} if this collection changed as a
 * result of the call. (Returns {@code false} if this collection does
 * not permit duplicates and already contains the specified element.)<p>
 *
 * Collections that support this operation may place limitations on what
 * elements may be added to this collection. In particular, some
 * collections will refuse to add {@code null} elements, and others will
 * impose restrictions on the type of elements that may be added.
 * Collection classes should clearly specify in their documentation any
 * restrictions on what elements may be added.<p>
 *
 * If a collection refuses to add a particular element for any reason
 * other than that it already contains the element, it <i>must</i> throw
 * an exception (rather than returning {@code false}). This preserves
 * the invariant that a collection always contains the specified element
 * after this call returns.
 *
 * @param e element whose presence in this collection is to be ensured
 * @return {@code true} if this collection changed as a result of the
 * call
 * @throws UnsupportedOperationException if the {@code add} operation
 * is not supported by this collection
 * @throws ClassCastException if the class of the specified element
 * prevents it from being added to this collection
 * @throws NullPointerException if the specified element is null and this
 * collection does not permit null elements
 * @throws IllegalArgumentException if some property of the element
 * prevents it from being added to this collection
 * @throws IllegalStateException if the element cannot be added at this
 * time due to insertion restrictions
 */
 boolean add(E e);

 /**
 * Removes a single instance of the specified element from this
 * collection, if it is present (optional operation). More formally,
 * removes an element {@code e} such that
 * {@code Objects.equals(o, e)}, if
 * this collection contains one or more such elements. Returns
 * {@code true} if this collection contained the specified element (or
 * equivalently, if this collection changed as a result of the call).
 *
 * @param o element to be removed from this collection, if present
 * @return {@code true} if an element was removed as a result of this call
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this collection
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * collection does not permit null elements
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws UnsupportedOperationException if the {@code remove} operation
 * is not supported by this collection
 */
 boolean remove(Object o);


 // Bulk Operations

 /**
 * Returns {@code true} if this collection contains all of the elements
 * in the specified collection.
 *
 * @param c collection to be checked for containment in this collection
 * @return {@code true} if this collection contains all of the elements
 * in the specified collection
 * @throws ClassCastException if the types of one or more elements
 * in the specified collection are incompatible with this
 * collection
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified collection contains one
 * or more null elements and this collection does not permit null
 * elements
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null.
 * @see #contains(Object)
 */
 boolean containsAll(Collection<?> c);

 /**
 * Adds all of the elements in the specified collection to this collection
 * (optional operation). The behavior of this operation is undefined if
 * the specified collection is modified while the operation is in progress.
 * (This implies that the behavior of this call is undefined if the
 * specified collection is this collection, and this collection is
 * nonempty.)
 *
 * @param c collection containing elements to be added to this collection
 * @return {@code true} if this collection changed as a result of the call
 * @throws UnsupportedOperationException if the {@code addAll} operation
 * is not supported by this collection
 * @throws ClassCastException if the class of an element of the specified
 * collection prevents it from being added to this collection
 * @throws NullPointerException if the specified collection contains a
 * null element and this collection does not permit null elements,
 * or if the specified collection is null
 * @throws IllegalArgumentException if some property of an element of the
 * specified collection prevents it from being added to this
 * collection
 * @throws IllegalStateException if not all the elements can be added at
 * this time due to insertion restrictions
 * @see #add(Object)
 */
 boolean addAll(Collection<? extends E> c);

 /**
 * Removes all of this collection's elements that are also contained in the
 * specified collection (optional operation). After this call returns,
 * this collection will contain no elements in common with the specified
 * collection.
 *
 * @param c collection containing elements to be removed from this collection
 * @return {@code true} if this collection changed as a result of the
 * call
 * @throws UnsupportedOperationException if the {@code removeAll} method
 * is not supported by this collection
 * @throws ClassCastException if the types of one or more elements
 * in this collection are incompatible with the specified
 * collection
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this collection contains one or more
 * null elements and the specified collection does not support
 * null elements
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 boolean removeAll(Collection<?> c);

 /**
 * Removes all of the elements of this collection that satisfy the given
 * predicate. Errors or runtime exceptions thrown during iteration or by
 * the predicate are relayed to the caller.
 *
 * @implSpec
 * The default implementation traverses all elements of the collection using
 * its {@link #iterator}. Each matching element is removed using
 * {@link Iterator#remove()}. If the collection's iterator does not
 * support removal then an {@code UnsupportedOperationException} will be
 * thrown on the first matching element.
 *
 * @param filter a predicate which returns {@code true} for elements to be
 * removed
 * @return {@code true} if any elements were removed
 * @throws NullPointerException if the specified filter is null
 * @throws UnsupportedOperationException if elements cannot be removed
 * from this collection. Implementations may throw this exception if a
 * matching element cannot be removed or if, in general, removal is not
 * supported.
 * @since 1.8
 */
 default boolean removeIf(Predicate<? super E> filter) {
 Objects.requireNonNull(filter);
 boolean removed = false;
 final Iterator<E> each = iterator();
 while (each.hasNext()) {
 if (filter.test(each.next())) {
 each.remove();
 removed = true;
 }
 }
 return removed;
 }

 /**
 * Retains only the elements in this collection that are contained in the
 * specified collection (optional operation). In other words, removes from
 * this collection all of its elements that are not contained in the
 * specified collection.
 *
 * @param c collection containing elements to be retained in this collection
 * @return {@code true} if this collection changed as a result of the call
 * @throws UnsupportedOperationException if the {@code retainAll} operation
 * is not supported by this collection
 * @throws ClassCastException if the types of one or more elements
 * in this collection are incompatible with the specified
 * collection
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this collection contains one or more
 * null elements and the specified collection does not permit null
 * elements
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 boolean retainAll(Collection<?> c);

 /**
 * Removes all of the elements from this collection (optional operation).
 * The collection will be empty after this method returns.
 *
 * @throws UnsupportedOperationException if the {@code clear} operation
 * is not supported by this collection
 */
 void clear();


 // Comparison and hashing

 /**
 * Compares the specified object with this collection for equality. <p>
 *
 * While the {@code Collection} interface adds no stipulations to the
 * general contract for the {@code Object.equals}, programmers who
 * implement the {@code Collection} interface "directly" (in other words,
 * create a class that is a {@code Collection} but is not a {@code Set}
 * or a {@code List}) must exercise care if they choose to override the
 * {@code Object.equals}. It is not necessary to do so, and the simplest
 * course of action is to rely on {@code Object}'s implementation, but
 * the implementor may wish to implement a "value comparison" in place of
 * the default "reference comparison." (The {@code List} and
 * {@code Set} interfaces mandate such value comparisons.)<p>
 *
 * The general contract for the {@code Object.equals} method states that
 * equals must be symmetric (in other words, {@code a.equals(b)} if and
 * only if {@code b.equals(a)}). The contracts for {@code List.equals}
 * and {@code Set.equals} state that lists are only equal to other lists,
 * and sets to other sets. Thus, a custom {@code equals} method for a
 * collection class that implements neither the {@code List} nor
 * {@code Set} interface must return {@code false} when this collection
 * is compared to any list or set. (By the same logic, it is not possible
 * to write a class that correctly implements both the {@code Set} and
 * {@code List} interfaces.)
 *
 * @param o object to be compared for equality with this collection
 * @return {@code true} if the specified object is equal to this
 * collection
 *
 * @see Object#equals(Object)
 * @see Set#equals(Object)
 * @see List#equals(Object)
 */
 boolean equals(Object o);

 /**
 * Returns the hash code value for this collection. While the
 * {@code Collection} interface adds no stipulations to the general
 * contract for the {@code Object.hashCode} method, programmers should
 * take note that any class that overrides the {@code Object.equals}
 * method must also override the {@code Object.hashCode} method in order
 * to satisfy the general contract for the {@code Object.hashCode} method.
 * In particular, {@code c1.equals(c2)} implies that
 * {@code c1.hashCode()==c2.hashCode()}.
 *
 * @return the hash code value for this collection
 *
 * @see Object#hashCode()
 * @see Object#equals(Object)
 */
 int hashCode();

 /**
 * Creates a {@link Spliterator} over the elements in this collection.
 *
 * Implementations should document characteristic values reported by the
 * spliterator. Such characteristic values are not required to be reported
 * if the spliterator reports {@link Spliterator#SIZED} and this collection
 * contains no elements.
 *
 * <p>The default implementation should be overridden by subclasses that
 * can return a more efficient spliterator. In order to
 * preserve expected laziness behavior for the {@link #stream()} and
 * {@link #parallelStream()} methods, spliterators should either have the
 * characteristic of {@code IMMUTABLE} or {@code CONCURRENT}, or be
 * <em><a href="Spliterator.html#binding">late-binding</a></em>.
 * If none of these is practical, the overriding class should describe the
 * spliterator's documented policy of binding and structural interference,
 * and should override the {@link #stream()} and {@link #parallelStream()}
 * methods to create streams using a {@code Supplier} of the spliterator,
 * as in:
 * <pre>{@code
 * Stream<E> s = StreamSupport.stream(() -> spliterator(), spliteratorCharacteristics)
 * }</pre>
 * <p>These requirements ensure that streams produced by the
 * {@link #stream()} and {@link #parallelStream()} methods will reflect the
 * contents of the collection as of initiation of the terminal stream
 * operation.
 *
 * @implSpec
 * The default implementation creates a
 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
 * from the collection's {@code Iterator}. The spliterator inherits the
 * <em>fail-fast</em> properties of the collection's iterator.
 * <p>
 * The created {@code Spliterator} reports {@link Spliterator#SIZED}.
 *
 * @implNote
 * The created {@code Spliterator} additionally reports
 * {@link Spliterator#SUBSIZED}.
 *
 * <p>If a spliterator covers no elements then the reporting of additional
 * characteristic values, beyond that of {@code SIZED} and {@code SUBSIZED},
 * does not aid clients to control, specialize or simplify computation.
 * However, this does enable shared use of an immutable and empty
 * spliterator instance (see {@link Spliterators#emptySpliterator()}) for
 * empty collections, and enables clients to determine if such a spliterator
 * covers no elements.
 *
 * @return a {@code Spliterator} over the elements in this collection
 * @since 1.8
 */
 @Override
 default Spliterator<E> spliterator() {
 return Spliterators.spliterator(this, 0);
 }

 /**
 * Returns a sequential {@code Stream} with this collection as its source.
 *
 * <p>This method should be overridden when the {@link #spliterator()}
 * method cannot return a spliterator that is {@code IMMUTABLE},
 * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
 * for details.)
 *
 * @implSpec
 * The default implementation creates a sequential {@code Stream} from the
 * collection's {@code Spliterator}.
 *
 * @return a sequential {@code Stream} over the elements in this collection
 * @since 1.8
 */
 default Stream<E> stream() {
 return StreamSupport.stream(spliterator(), false);
 }

 /**
 * Returns a possibly parallel {@code Stream} with this collection as its
 * source. It is allowable for this method to return a sequential stream.
 *
 * <p>This method should be overridden when the {@link #spliterator()}
 * method cannot return a spliterator that is {@code IMMUTABLE},
 * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
 * for details.)
 *
 * @implSpec
 * The default implementation creates a parallel {@code Stream} from the
 * collection's {@code Spliterator}.
 *
 * @return a possibly parallel {@code Stream} over the elements in this
 * collection
 * @since 1.8
 */
 default Stream<E> parallelStream() {
 return StreamSupport.stream(spliterator(), true);
 }
}