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	/*
	* Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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 — if changes
	* are permitted — 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);
	}
	}

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