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Diffstat (limited to 'libjava/java/util/HashSet.java')
| -rw-r--r-- | libjava/java/util/HashSet.java | 221 |
1 files changed, 221 insertions, 0 deletions
diff --git a/libjava/java/util/HashSet.java b/libjava/java/util/HashSet.java new file mode 100644 index 0000000..f7cb326 --- /dev/null +++ b/libjava/java/util/HashSet.java @@ -0,0 +1,221 @@ +/* HashSet.java -- a class providing a HashMap-backet Set + Copyright (C) 1998, 1999 Free Software Foundation, Inc. + +This file is part of GNU Classpath. + +GNU Classpath is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2, or (at your option) +any later version. + +GNU Classpath 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 for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; see the file COPYING. If not, write to the +Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA +02111-1307 USA. + +As a special exception, if you link this library with other files to +produce an executable, this library does not by itself cause the +resulting executable to be covered by the GNU General Public License. +This exception does not however invalidate any other reasons why the +executable file might be covered by the GNU General Public License. */ + + +package java.util; + +import java.io.IOException; +import java.io.Serializable; +import java.io.ObjectInputStream; +import java.io.ObjectOutputStream; + +/** + * This class provides a HashMap-backed implementation of the + * Set interface. + * + * Each element in the Set is a key in the backing HashMap; each key + * maps to a static token, denoting that the key does, in fact, exist. + * + * Most operations are O(1), assuming no hash collisions. In the worst + * case (where all hases collide), operations are O(n). + * + * HashSet is a part of the JDK1.2 Collections API. + * + * @author Jon Zeppieri + * @version $Revision: 1.5 $ + * @modified $Id: HashSet.java,v 1.5 2000/10/26 10:19:00 bryce Exp $ + */ +public class HashSet extends AbstractSet + implements Set, Cloneable, Serializable +{ + /** the HashMap which backs this Set */ + transient HashMap map; + static final long serialVersionUID = -5024744406713321676L; + + /** + * construct a new, empty HashSet whose backing HashMap has the default + * capacity and loadFacor + */ + public HashSet() + { + map = new HashMap(); + } + + /** + * construct a new, empty HashSet whose backing HashMap has the supplied + * capacity and the default load factor + * + * @param initialCapacity the initial capacity of the backing + * HashMap + */ + public HashSet(int initialCapacity) + { + map = new HashMap(initialCapacity); + } + + /** + * construct a new, empty HashSet whose backing HashMap has the supplied + * capacity and load factor + * + * @param initialCapacity the initial capacity of the backing + * HashMap + * @param loadFactor the load factor of the backing HashMap + */ + public HashSet(int initialCapacity, float loadFactor) + { + map = new HashMap(initialCapacity, loadFactor); + } + + /** + * construct a new HashSet with the same elements as are in the supplied + * collection (eliminating any duplicates, of course; the backing HashMap + * will have the default capacity and load factor + * + * @param c a collection containing the elements with + * which this set will be initialized + */ + public HashSet(Collection c) + { + map = new HashMap(); + addAll(c); + } + + /** + * adds the given Object to the set if it is not already in the Set, + * returns true if teh element was added, false otherwise + * + * @param o the Object to add to this Set + */ + public boolean add(Object o) + { + return (map.put(o, Boolean.TRUE) == null); + } + + /** + * empties this Set of all elements; this is a fast operation [O(1)] + */ + public void clear() + { + map.clear(); + } + + /** + * returns a shallow copy of this Set (the Set itself is cloned; its + * elements are not) + */ + public Object clone() + { + HashSet copy = null; + try + { + copy = (HashSet) super.clone(); + copy.map = (HashMap) map.clone(); + } + catch (CloneNotSupportedException ex) + { + } + + return copy; + } + + /** + * returns true if the supplied element is in this Set, false otherwise + * + * @param o the Object whose presence in this Set we are testing for + */ + public boolean contains(Object o) + { + return map.containsKey(o); + } + + /** + * returns true if this set has no elements in it (size() == 0) + */ + public boolean isEmpty() + { + return map.isEmpty(); + } + + /** + * returns an Iterator over the elements of this Set; the Iterator allows + * removal of elements + */ + public Iterator iterator() + { + return map.keySet().iterator(); + } + + /** + * removes the supplied Object from this Set if it is in the Set; returns + * true if an element was removed, false otherwise + */ + public boolean remove(Object o) + { + return (map.remove(o) != null); + } + + /** + * returns the number of elements in this Set + */ + public int size() + { + return map.size(); + } + + /** Serialize this Object in a manner which is binary-compatible with the + * JDK */ + private void writeObject(ObjectOutputStream s) throws IOException + { + Iterator it = iterator(); + s.writeInt(map.buckets.length); + s.writeFloat(map.loadFactor); + s.writeInt(map.size); + while (it.hasNext()) + s.writeObject(it.next()); + } + + /** Deserialize this Object in a manner which is binary-compatible with + * the JDK */ + private void readObject(ObjectInputStream s) throws IOException, + ClassNotFoundException + { + int i, size, capacity; + float loadFactor; + Object element; + + capacity = s.readInt(); + loadFactor = s.readFloat(); + size = s.readInt(); + + map = new HashMap(capacity, loadFactor); + + for (i = 0; i < size; i++) + { + element = s.readObject(); + map.put(element, Boolean.TRUE); + } + } +} |