jaroslav@557: /*
jaroslav@557:  * Copyright (c) 1997, 2006, Oracle and/or its affiliates. All rights reserved.
jaroslav@557:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@557:  *
jaroslav@557:  * This code is free software; you can redistribute it and/or modify it
jaroslav@557:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@557:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@557:  * particular file as subject to the "Classpath" exception as provided
jaroslav@557:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@557:  *
jaroslav@557:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@557:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@557:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@557:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@557:  * accompanied this code).
jaroslav@557:  *
jaroslav@557:  * You should have received a copy of the GNU General Public License version
jaroslav@557:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@557:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@557:  *
jaroslav@557:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@557:  * or visit www.oracle.com if you need additional information or have any
jaroslav@557:  * questions.
jaroslav@557:  */
jaroslav@557: 
jaroslav@557: package java.util;
jaroslav@557: 
jaroslav@557: /**
jaroslav@557:  * This class provides a skeletal implementation of the <tt>Set</tt>
jaroslav@557:  * interface to minimize the effort required to implement this
jaroslav@557:  * interface. <p>
jaroslav@557:  *
jaroslav@557:  * The process of implementing a set by extending this class is identical
jaroslav@557:  * to that of implementing a Collection by extending AbstractCollection,
jaroslav@557:  * except that all of the methods and constructors in subclasses of this
jaroslav@557:  * class must obey the additional constraints imposed by the <tt>Set</tt>
jaroslav@557:  * interface (for instance, the add method must not permit addition of
jaroslav@557:  * multiple instances of an object to a set).<p>
jaroslav@557:  *
jaroslav@557:  * Note that this class does not override any of the implementations from
jaroslav@557:  * the <tt>AbstractCollection</tt> class.  It merely adds implementations
jaroslav@557:  * for <tt>equals</tt> and <tt>hashCode</tt>.<p>
jaroslav@557:  *
jaroslav@557:  * This class is a member of the
jaroslav@557:  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
jaroslav@557:  * Java Collections Framework</a>.
jaroslav@557:  *
jaroslav@557:  * @param <E> the type of elements maintained by this set
jaroslav@557:  *
jaroslav@557:  * @author  Josh Bloch
jaroslav@557:  * @author  Neal Gafter
jaroslav@557:  * @see Collection
jaroslav@557:  * @see AbstractCollection
jaroslav@557:  * @see Set
jaroslav@557:  * @since 1.2
jaroslav@557:  */
jaroslav@557: 
jaroslav@557: public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {
jaroslav@557:     /**
jaroslav@557:      * Sole constructor.  (For invocation by subclass constructors, typically
jaroslav@557:      * implicit.)
jaroslav@557:      */
jaroslav@557:     protected AbstractSet() {
jaroslav@557:     }
jaroslav@557: 
jaroslav@557:     // Comparison and hashing
jaroslav@557: 
jaroslav@557:     /**
jaroslav@557:      * Compares the specified object with this set for equality.  Returns
jaroslav@557:      * <tt>true</tt> if the given object is also a set, the two sets have
jaroslav@557:      * the same size, and every member of the given set is contained in
jaroslav@557:      * this set.  This ensures that the <tt>equals</tt> method works
jaroslav@557:      * properly across different implementations of the <tt>Set</tt>
jaroslav@557:      * interface.<p>
jaroslav@557:      *
jaroslav@557:      * This implementation first checks if the specified object is this
jaroslav@557:      * set; if so it returns <tt>true</tt>.  Then, it checks if the
jaroslav@557:      * specified object is a set whose size is identical to the size of
jaroslav@557:      * this set; if not, it returns false.  If so, it returns
jaroslav@557:      * <tt>containsAll((Collection) o)</tt>.
jaroslav@557:      *
jaroslav@557:      * @param o object to be compared for equality with this set
jaroslav@557:      * @return <tt>true</tt> if the specified object is equal to this set
jaroslav@557:      */
jaroslav@557:     public boolean equals(Object o) {
jaroslav@557:         if (o == this)
jaroslav@557:             return true;
jaroslav@557: 
jaroslav@557:         if (!(o instanceof Set))
jaroslav@557:             return false;
jaroslav@557:         Collection c = (Collection) o;
jaroslav@557:         if (c.size() != size())
jaroslav@557:             return false;
jaroslav@557:         try {
jaroslav@557:             return containsAll(c);
jaroslav@557:         } catch (ClassCastException unused)   {
jaroslav@557:             return false;
jaroslav@557:         } catch (NullPointerException unused) {
jaroslav@557:             return false;
jaroslav@557:         }
jaroslav@557:     }
jaroslav@557: 
jaroslav@557:     /**
jaroslav@557:      * Returns the hash code value for this set.  The hash code of a set is
jaroslav@557:      * defined to be the sum of the hash codes of the elements in the set,
jaroslav@557:      * where the hash code of a <tt>null</tt> element is defined to be zero.
jaroslav@557:      * This ensures that <tt>s1.equals(s2)</tt> implies that
jaroslav@557:      * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
jaroslav@557:      * and <tt>s2</tt>, as required by the general contract of
jaroslav@557:      * {@link Object#hashCode}.
jaroslav@557:      *
jaroslav@557:      * <p>This implementation iterates over the set, calling the
jaroslav@557:      * <tt>hashCode</tt> method on each element in the set, and adding up
jaroslav@557:      * the results.
jaroslav@557:      *
jaroslav@557:      * @return the hash code value for this set
jaroslav@557:      * @see Object#equals(Object)
jaroslav@557:      * @see Set#equals(Object)
jaroslav@557:      */
jaroslav@557:     public int hashCode() {
jaroslav@557:         int h = 0;
jaroslav@557:         Iterator<E> i = iterator();
jaroslav@557:         while (i.hasNext()) {
jaroslav@557:             E obj = i.next();
jaroslav@557:             if (obj != null)
jaroslav@557:                 h += obj.hashCode();
jaroslav@557:         }
jaroslav@557:         return h;
jaroslav@557:     }
jaroslav@557: 
jaroslav@557:     /**
jaroslav@557:      * Removes from this set all of its elements that are contained in the
jaroslav@557:      * specified collection (optional operation).  If the specified
jaroslav@557:      * collection is also a set, this operation effectively modifies this
jaroslav@557:      * set so that its value is the <i>asymmetric set difference</i> of
jaroslav@557:      * the two sets.
jaroslav@557:      *
jaroslav@557:      * <p>This implementation determines which is the smaller of this set
jaroslav@557:      * and the specified collection, by invoking the <tt>size</tt>
jaroslav@557:      * method on each.  If this set has fewer elements, then the
jaroslav@557:      * implementation iterates over this set, checking each element
jaroslav@557:      * returned by the iterator in turn to see if it is contained in
jaroslav@557:      * the specified collection.  If it is so contained, it is removed
jaroslav@557:      * from this set with the iterator's <tt>remove</tt> method.  If
jaroslav@557:      * the specified collection has fewer elements, then the
jaroslav@557:      * implementation iterates over the specified collection, removing
jaroslav@557:      * from this set each element returned by the iterator, using this
jaroslav@557:      * set's <tt>remove</tt> method.
jaroslav@557:      *
jaroslav@557:      * <p>Note that this implementation will throw an
jaroslav@557:      * <tt>UnsupportedOperationException</tt> if the iterator returned by the
jaroslav@557:      * <tt>iterator</tt> method does not implement the <tt>remove</tt> method.
jaroslav@557:      *
jaroslav@557:      * @param  c collection containing elements to be removed from this set
jaroslav@557:      * @return <tt>true</tt> if this set changed as a result of the call
jaroslav@557:      * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
jaroslav@557:      *         is not supported by this set
jaroslav@557:      * @throws ClassCastException if the class of an element of this set
jaroslav@557:      *         is incompatible with the specified collection
jaroslav@557:      * (<a href="Collection.html#optional-restrictions">optional</a>)
jaroslav@557:      * @throws NullPointerException if this set contains a null element and the
jaroslav@557:      *         specified collection does not permit null elements
jaroslav@557:      * (<a href="Collection.html#optional-restrictions">optional</a>),
jaroslav@557:      *         or if the specified collection is null
jaroslav@557:      * @see #remove(Object)
jaroslav@557:      * @see #contains(Object)
jaroslav@557:      */
jaroslav@557:     public boolean removeAll(Collection<?> c) {
jaroslav@557:         boolean modified = false;
jaroslav@557: 
jaroslav@557:         if (size() > c.size()) {
jaroslav@557:             for (Iterator<?> i = c.iterator(); i.hasNext(); )
jaroslav@557:                 modified |= remove(i.next());
jaroslav@557:         } else {
jaroslav@557:             for (Iterator<?> i = iterator(); i.hasNext(); ) {
jaroslav@557:                 if (c.contains(i.next())) {
jaroslav@557:                     i.remove();
jaroslav@557:                     modified = true;
jaroslav@557:                 }
jaroslav@557:             }
jaroslav@557:         }
jaroslav@557:         return modified;
jaroslav@557:     }
jaroslav@557: 
jaroslav@557: }