140 lines
5.0 KiB
Java
140 lines
5.0 KiB
Java
/* AbstractSet.java -- Abstract implementation of most of Set
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Copyright (C) 1998, 2000, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util;
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/**
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* An abstract implementation of Set to make it easier to create your own
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* implementations. In order to create a Set, subclass AbstractSet and
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* implement the same methods that are required for AbstractCollection
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* (although these methods must of course meet the requirements that Set puts
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* on them - specifically, no element may be in the set more than once). This
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* class simply provides implementations of equals() and hashCode() to fulfil
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* the requirements placed on them by the Set interface.
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*
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* @author Original author unknown
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* @author Eric Blake <ebb9@email.byu.edu>
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* @see Collection
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* @see AbstractCollection
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* @see Set
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* @see HashSet
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* @see TreeSet
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* @see LinkedHashSet
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* @since 1.2
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* @status updated to 1.4
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*/
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public abstract class AbstractSet extends AbstractCollection implements Set
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{
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/**
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* The main constructor, for use by subclasses.
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*/
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protected AbstractSet()
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{
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}
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/**
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* Tests whether the given object is equal to this Set. This implementation
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* first checks whether this set <em>is</em> the given object, and returns
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* true if so. Otherwise, if o is a Set and is the same size as this one, it
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* returns the result of calling containsAll on the given Set. Otherwise, it
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* returns false.
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*
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* @param o the Object to be tested for equality with this Set
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* @return true if the given object is equal to this Set
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*/
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public boolean equals(Object o)
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{
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return (o == this ||
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(o instanceof Set && ((Set) o).size() == size()
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&& containsAll((Collection) o)));
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}
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/**
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* Returns a hash code for this Set. The hash code of a Set is the sum of the
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* hash codes of all its elements, except that the hash code of null is
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* defined to be zero. This implementation obtains an Iterator over the Set,
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* and sums the results.
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*
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* @return a hash code for this Set
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*/
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public int hashCode()
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{
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Iterator itr = iterator();
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int hash = 0;
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int pos = size();
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while (--pos >= 0)
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hash += hashCode(itr.next());
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return hash;
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}
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/**
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* Removes from this set all elements in the given collection (optional
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* operation). This implementation uses <code>size()</code> to determine
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* the smaller collection. Then, if this set is smaller, it iterates
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* over the set, calling Iterator.remove if the collection contains
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* the element. If this set is larger, it iterates over the collection,
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* calling Set.remove for all elements in the collection. Note that
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* this operation will fail if a remove methods is not supported.
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*
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* @param c the collection of elements to remove
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* @return true if the set was modified as a result
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* @throws UnsupportedOperationException if remove is not supported
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* @throws NullPointerException if the collection is null
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* @see AbstractCollection#remove(Object)
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* @see Collection#contains(Object)
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* @see Iterator#remove()
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*/
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public boolean removeAll(Collection c)
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{
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int oldsize = size();
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int count = c.size();
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Iterator i;
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if (oldsize < count)
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{
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for (i = iterator(), count = oldsize; count > 0; count--)
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if (c.contains(i.next()))
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i.remove();
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}
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else
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for (i = c.iterator(); count > 0; count--)
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remove(i.next());
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return oldsize != size();
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}
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}
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