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	/*
	* Copyright (c) 1997, 2013, 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
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.util;

	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 <tt>Set</tt> and <tt>List</tt>. 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 <tt>Collection</tt> implementation classes (which
	* typically implement <tt>Collection</tt> 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 <tt>Collection</tt>, 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 <tt>Collection</tt>
	* implementations in the Java platform libraries comply.
	*
	* <p>The "destructive" methods contained in this interface, that is, the
	* methods that modify the collection on which they operate, are specified to
	* throw <tt>UnsupportedOperationException</tt> if this collection does not
	* support the operation. If this is the case, these methods may, but are not
	* required to, throw an <tt>UnsupportedOperationException</tt> if the
	* invocation would have no effect on the collection. For example, invoking
	* the {@link #addAll(Collection)} method on an unmodifiable collection may,
	* but is not required to, throw the exception if the collection to be added
	* is empty.
	*
	* <p><a name="optional-restrictions">
	* Some collection implementations have restrictions on the elements that
	* they may contain.</a> 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
	* <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. 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 <tt>true</tt> if and only if this collection
	* contains at least one element <tt>e</tt> such that
	* <tt>(o==null ? e==null : o.equals(e))</tt>." This specification should
	* <i>not</i> be construed to imply that invoking <tt>Collection.contains</tt>
	* with a non-null argument <tt>o</tt> will cause <tt>o.equals(e)</tt> to be
	* invoked for any element <tt>e</tt>. Implementations are free to implement
	* optimizations whereby the <tt>equals</tt> 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.
	*
	* <p>This interface is a member of the
	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
	* 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 <tt>Integer.MAX_VALUE</tt> elements, returns
	* <tt>Integer.MAX_VALUE</tt>.
	*
	* @return the number of elements in this collection
	*/
	int size();

	/**
	* Returns <tt>true</tt> if this collection contains no elements.
	*
	* @return <tt>true</tt> if this collection contains no elements
	*/
	boolean isEmpty();

	/**
	* Returns <tt>true</tt> if this collection contains the specified element.
	* More formally, returns <tt>true</tt> if and only if this collection
	* contains at least one element <tt>e</tt> such that
	* <tt>(o==null ? e==null : o.equals(e))</tt>.
	*
	* @param o element whose presence in this collection is to be tested
	* @return <tt>true</tt> if this collection contains the specified
	* element
	* @throws ClassCastException if the type of the specified element
	* is incompatible with this collection
	* (<a href="#optional-restrictions">optional</a>)
	* @throws NullPointerException if the specified element is null and this
	* collection does not permit null elements
	* (<a href="#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 <tt>Iterator</tt> 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.
	*
	* <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.
	*
	* <p>This method acts as bridge between array-based and collection-based
	* APIs.
	*
	* @return an array 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
	* <tt>null</tt>. (This is useful in determining the length of this
	* collection <i>only</i> if the caller knows that this collection does
	* not contain any <tt>null</tt> 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.
	*
	* <p>Like the {@link #toArray()} method, this method acts as bridge between
	* array-based and collection-based APIs. Further, this method allows
	* precise control over the runtime type of the output array, and may,
	* under certain circumstances, be used to save allocation costs.
	*
	* <p>Suppose <tt>x</tt> is a collection known to contain only strings.
	* The following code can be used to dump the collection into a newly
	* allocated array of <tt>String</tt>:
	*
	* <pre>
	* String[] y = x.toArray(new String[0]);</pre>
	*
	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
	* <tt>toArray()</tt>.
	*
	* @param <T> the runtime 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 the specified array
	* is not a supertype of the runtime type of every element in
	* this collection
	* @throws NullPointerException if the specified array is null
	*/
	<T> T[] toArray(T[] a);

	// Modification Operations

	/**
	* Ensures that this collection contains the specified element (optional
	* operation). Returns <tt>true</tt> if this collection changed as a
	* result of the call. (Returns <tt>false</tt> 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 <tt>null</tt> 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 <tt>false</tt>). 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 <tt>true</tt> if this collection changed as a result of the
	* call
	* @throws UnsupportedOperationException if the <tt>add</tt> 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 <tt>e</tt> such that
	* <tt>(o==null ? e==null : o.equals(e))</tt>, if
	* this collection contains one or more such elements. Returns
	* <tt>true</tt> 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 <tt>true</tt> 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="#optional-restrictions">optional</a>)
	* @throws NullPointerException if the specified element is null and this
	* collection does not permit null elements
	* (<a href="#optional-restrictions">optional</a>)
	* @throws UnsupportedOperationException if the <tt>remove</tt> operation
	* is not supported by this collection
	*/
	boolean remove(Object o);


	// Bulk Operations

	/**
	* Returns <tt>true</tt> if this collection contains all of the elements
	* in the specified collection.
	*
	* @param c collection to be checked for containment in this collection
	* @return <tt>true</tt> 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="#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="#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 <tt>true</tt> if this collection changed as a result of the call
	* @throws UnsupportedOperationException if the <tt>addAll</tt> 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 <tt>true</tt> if this collection changed as a result of the
	* call
	* @throws UnsupportedOperationException if the <tt>removeAll</tt> 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="#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="#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 <tt>true</tt> if this collection changed as a result of the call
	* @throws UnsupportedOperationException if the <tt>retainAll</tt> 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="#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="#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 <tt>clear</tt> operation
	* is not supported by this collection
	*/
	void clear();


	// Comparison and hashing

	/**
	* Compares the specified object with this collection for equality. <p>
	*
	* While the <tt>Collection</tt> interface adds no stipulations to the
	* general contract for the <tt>Object.equals</tt>, programmers who
	* implement the <tt>Collection</tt> interface "directly" (in other words,
	* create a class that is a <tt>Collection</tt> but is not a <tt>Set</tt>
	* or a <tt>List</tt>) must exercise care if they choose to override the
	* <tt>Object.equals</tt>. It is not necessary to do so, and the simplest
	* course of action is to rely on <tt>Object</tt>'s implementation, but
	* the implementor may wish to implement a "value comparison" in place of
	* the default "reference comparison." (The <tt>List</tt> and
	* <tt>Set</tt> interfaces mandate such value comparisons.)<p>
	*
	* The general contract for the <tt>Object.equals</tt> method states that
	* equals must be symmetric (in other words, <tt>a.equals(b)</tt> if and
	* only if <tt>b.equals(a)</tt>). The contracts for <tt>List.equals</tt>
	* and <tt>Set.equals</tt> state that lists are only equal to other lists,
	* and sets to other sets. Thus, a custom <tt>equals</tt> method for a
	* collection class that implements neither the <tt>List</tt> nor
	* <tt>Set</tt> interface must return <tt>false</tt> 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 <tt>Set</tt> and
	* <tt>List</tt> interfaces.)
	*
	* @param o object to be compared for equality with this collection
	* @return <tt>true</tt> 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
	* <tt>Collection</tt> interface adds no stipulations to the general
	* contract for the <tt>Object.hashCode</tt> method, programmers should
	* take note that any class that overrides the <tt>Object.equals</tt>
	* method must also override the <tt>Object.hashCode</tt> method in order
	* to satisfy the general contract for the <tt>Object.hashCode</tt> method.
	* In particular, <tt>c1.equals(c2)</tt> implies that
	* <tt>c1.hashCode()==c2.hashCode()</tt>.
	*
	* @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 collections'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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