/*
* @(#)AbstractSet.java 1.21 06/10/10
*
* Copyright 1990-2008 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
*
* This program 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.
*
* This program 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 at /legal/license.txt).
*
* 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 Sun Microsystems, Inc., 4150 Network Circle, Santa
* Clara, CA 95054 or visit www.sun.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 intances 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}/../guide/collections/index.html">
* Java Collections Framework</a>.
*
* @author Josh Bloch
* @version 1.14, 02/02/00
* @see Collection
* @see AbstractCollection
* @see Set
* @since 1.2
*/
public abstract class AbstractSet extends AbstractCollection implements Set {
/**
* 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 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.
* 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
* Object.hashCode.<p>
*
* This implementation enumerates over the set, calling the
* <tt>hashCode</tt> method on each element in the collection, and
* adding up the results.
*
* @return the hash code value for this set.
*/
public int hashCode() {
int h = 0;
Iterator i = iterator();
while (i.hasNext()) {
Object 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).<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 elements to be removed from this set.
* @return <tt>true</tt> if this set changed as a result of the call.
*
* @throws UnsupportedOperationException removeAll is not supported
* by this set.
* @throws NullPointerException 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;
}
}