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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;

	/**
	* This class provides a skeletal implementation of the <tt>Set</tt>
	* interface to minimize the effort required to implement this
	* interface. <p>
	*
	* The process of implementing a set by extending this class is identical
	* to that of implementing a Collection by extending AbstractCollection,
	* except that all of the methods and constructors in subclasses of this
	* class must obey the additional constraints imposed by the <tt>Set</tt>
	* interface (for instance, the add method must not permit addition of
	* multiple instances of an object to a set).<p>
	*
	* Note that this class does not override any of the implementations from
	* the <tt>AbstractCollection</tt> class. It merely adds implementations
	* for <tt>equals</tt> and <tt>hashCode</tt>.<p>
	*
	* This class is a member of the
	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
	* Java Collections Framework</a>.
	*
	* @param <E> the type of elements maintained by this set
	*
	* @author Josh Bloch
	* @author Neal Gafter
	* @see Collection
	* @see AbstractCollection
	* @see Set
	* @since 1.2
	*/

	public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {
	/**
	* Sole constructor. (For invocation by subclass constructors, typically
	* implicit.)
	*/
	protected AbstractSet() {
	}

	// Comparison and hashing

	/**
	* Compares the specified object with this set for equality. Returns
	* <tt>true</tt> if the given object is also a set, the two sets have
	* the same size, and every member of the given set is contained in
	* this set. This ensures that the <tt>equals</tt> method works
	* properly across different implementations of the <tt>Set</tt>
	* interface.<p>
	*
	* This implementation first checks if the specified object is this
	* set; if so it returns <tt>true</tt>. Then, it checks if the
	* specified object is a set whose size is identical to the size of
	* this set; if not, it returns false. If so, it returns
	* <tt>containsAll((Collection) o)</tt>.
	*
	* @param o object to be compared for equality with this set
	* @return <tt>true</tt> if the specified object is equal to this set
	*/
	public boolean equals(Object o) {
	if (o == this)
	return true;

	if (!(o instanceof Set))
	return false;
	Collection<?> c = (Collection<?>) o;
	if (c.size() != size())
	return false;
	try {
	return containsAll(c);
	} catch (ClassCastException unused) {
	return false;
	} catch (NullPointerException unused) {
	return false;
	}
	}

	/**
	* Returns the hash code value for this set. The hash code of a set is
	* defined to be the sum of the hash codes of the elements in the set,
	* where the hash code of a <tt>null</tt> element is defined to be zero.
	* This ensures that <tt>s1.equals(s2)</tt> implies that
	* <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
	* and <tt>s2</tt>, as required by the general contract of
	* {@link Object#hashCode}.
	*
	* <p>This implementation iterates over the set, calling the
	* <tt>hashCode</tt> method on each element in the set, and adding up
	* the results.
	*
	* @return the hash code value for this set
	* @see Object#equals(Object)
	* @see Set#equals(Object)
	*/
	public int hashCode() {
	int h = 0;
	Iterator<E> i = iterator();
	while (i.hasNext()) {
	E obj = i.next();
	if (obj != null)
	h += obj.hashCode();
	}
	return h;
	}

	/**
	* Removes from this set all of its elements that are contained in the
	* specified collection (optional operation). If the specified
	* collection is also a set, this operation effectively modifies this
	* set so that its value is the <i>asymmetric set difference</i> of
	* the two sets.
	*
	* <p>This implementation determines which is the smaller of this set
	* and the specified collection, by invoking the <tt>size</tt>
	* method on each. If this set has fewer elements, then the
	* implementation iterates over this set, checking each element
	* returned by the iterator in turn to see if it is contained in
	* the specified collection. If it is so contained, it is removed
	* from this set with the iterator's <tt>remove</tt> method. If
	* the specified collection has fewer elements, then the
	* implementation iterates over the specified collection, removing
	* from this set each element returned by the iterator, using this
	* set's <tt>remove</tt> method.
	*
	* <p>Note that this implementation will throw an
	* <tt>UnsupportedOperationException</tt> if the iterator returned by the
	* <tt>iterator</tt> method does not implement the <tt>remove</tt> method.
	*
	* @param c collection containing elements to be removed from this set
	* @return <tt>true</tt> if this set changed as a result of the call
	* @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
	* is not supported by this set
	* @throws ClassCastException if the class of an element of this set
	* is incompatible with the specified collection
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if this set contains a null element and the
	* specified collection does not permit null elements
	* (<a href="Collection.html#optional-restrictions">optional</a>),
	* or if the specified collection is null
	* @see #remove(Object)
	* @see #contains(Object)
	*/
	public boolean removeAll(Collection<?> c) {
	Objects.requireNonNull(c);
	boolean modified = false;

	if (size() > c.size()) {
	for (Iterator<?> i = c.iterator(); i.hasNext(); )
	modified \|= remove(i.next());
	} else {
	for (Iterator<?> i = iterator(); i.hasNext(); ) {
	if (c.contains(i.next())) {
	i.remove();
	modified = true;
	}
	}
	}
	return modified;
	}

	}

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