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  * 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

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  * 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;

 /**

  * 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) {

         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;

     }

 }