001/* HashSet.java -- a class providing a HashMap-backed Set 002 Copyright (C) 1998, 1999, 2001, 2004, 2005 Free Software Foundation, Inc. 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038 039package java.util; 040 041import java.io.IOException; 042import java.io.ObjectInputStream; 043import java.io.ObjectOutputStream; 044import java.io.Serializable; 045 046/** 047 * This class provides a HashMap-backed implementation of the Set interface. 048 * <p> 049 * 050 * Most operations are O(1), assuming no hash collisions. In the worst 051 * case (where all hashes collide), operations are O(n). Setting the 052 * initial capacity too low will force many resizing operations, but 053 * setting the initial capacity too high (or loadfactor too low) leads 054 * to wasted memory and slower iteration. 055 * <p> 056 * 057 * HashSet accepts the null key and null values. It is not synchronized, 058 * so if you need multi-threaded access, consider using:<br> 059 * <code>Set s = Collections.synchronizedSet(new HashSet(...));</code> 060 * <p> 061 * 062 * The iterators are <i>fail-fast</i>, meaning that any structural 063 * modification, except for <code>remove()</code> called on the iterator 064 * itself, cause the iterator to throw a 065 * {@link ConcurrentModificationException} rather than exhibit 066 * non-deterministic behavior. 067 * 068 * @author Jon Zeppieri 069 * @author Eric Blake (ebb9@email.byu.edu) 070 * @see Collection 071 * @see Set 072 * @see TreeSet 073 * @see Collections#synchronizedSet(Set) 074 * @see HashMap 075 * @see LinkedHashSet 076 * @since 1.2 077 * @status updated to 1.4 078 */ 079public class HashSet<T> extends AbstractSet<T> 080 implements Set<T>, Cloneable, Serializable 081{ 082 /** 083 * Compatible with JDK 1.2. 084 */ 085 private static final long serialVersionUID = -5024744406713321676L; 086 087 /** 088 * The HashMap which backs this Set. 089 */ 090 private transient HashMap<T, String> map; 091 092 /** 093 * Construct a new, empty HashSet whose backing HashMap has the default 094 * capacity (11) and loadFacor (0.75). 095 */ 096 public HashSet() 097 { 098 this(HashMap.DEFAULT_CAPACITY, HashMap.DEFAULT_LOAD_FACTOR); 099 } 100 101 /** 102 * Construct a new, empty HashSet whose backing HashMap has the supplied 103 * capacity and the default load factor (0.75). 104 * 105 * @param initialCapacity the initial capacity of the backing HashMap 106 * @throws IllegalArgumentException if the capacity is negative 107 */ 108 public HashSet(int initialCapacity) 109 { 110 this(initialCapacity, HashMap.DEFAULT_LOAD_FACTOR); 111 } 112 113 /** 114 * Construct a new, empty HashSet whose backing HashMap has the supplied 115 * capacity and load factor. 116 * 117 * @param initialCapacity the initial capacity of the backing HashMap 118 * @param loadFactor the load factor of the backing HashMap 119 * @throws IllegalArgumentException if either argument is negative, or 120 * if loadFactor is POSITIVE_INFINITY or NaN 121 */ 122 public HashSet(int initialCapacity, float loadFactor) 123 { 124 map = init(initialCapacity, loadFactor); 125 } 126 127 /** 128 * Construct a new HashSet with the same elements as are in the supplied 129 * collection (eliminating any duplicates, of course). The backing storage 130 * has twice the size of the collection, or the default size of 11, 131 * whichever is greater; and the default load factor (0.75). 132 * 133 * @param c a collection of initial set elements 134 * @throws NullPointerException if c is null 135 */ 136 public HashSet(Collection<? extends T> c) 137 { 138 this(Math.max(2 * c.size(), HashMap.DEFAULT_CAPACITY)); 139 addAll(c); 140 } 141 142 /** 143 * Adds the given Object to the set if it is not already in the Set. 144 * This set permits a null element. 145 * 146 * @param o the Object to add to this Set 147 * @return true if the set did not already contain o 148 */ 149 public boolean add(T o) 150 { 151 return map.put(o, "") == null; 152 } 153 154 /** 155 * Empties this Set of all elements; this takes constant time. 156 */ 157 public void clear() 158 { 159 map.clear(); 160 } 161 162 /** 163 * Returns a shallow copy of this Set. The Set itself is cloned; its 164 * elements are not. 165 * 166 * @return a shallow clone of the set 167 */ 168 public Object clone() 169 { 170 HashSet<T> copy = null; 171 try 172 { 173 copy = (HashSet<T>) super.clone(); 174 } 175 catch (CloneNotSupportedException x) 176 { 177 // Impossible to get here. 178 } 179 copy.map = (HashMap<T, String>) map.clone(); 180 return copy; 181 } 182 183 /** 184 * Returns true if the supplied element is in this Set. 185 * 186 * @param o the Object to look for 187 * @return true if it is in the set 188 */ 189 public boolean contains(Object o) 190 { 191 return map.containsKey(o); 192 } 193 194 /** 195 * Returns true if this set has no elements in it. 196 * 197 * @return <code>size() == 0</code>. 198 */ 199 public boolean isEmpty() 200 { 201 return map.size == 0; 202 } 203 204 /** 205 * Returns an Iterator over the elements of this Set, which visits the 206 * elements in no particular order. For this class, the Iterator allows 207 * removal of elements. The iterator is fail-fast, and will throw a 208 * ConcurrentModificationException if the set is modified externally. 209 * 210 * @return a set iterator 211 * @see ConcurrentModificationException 212 */ 213 public Iterator<T> iterator() 214 { 215 // Avoid creating intermediate keySet() object by using non-public API. 216 return map.iterator(HashMap.KEYS); 217 } 218 219 /** 220 * Removes the supplied Object from this Set if it is in the Set. 221 * 222 * @param o the object to remove 223 * @return true if an element was removed 224 */ 225 public boolean remove(Object o) 226 { 227 return (map.remove(o) != null); 228 } 229 230 /** 231 * Returns the number of elements in this Set (its cardinality). 232 * 233 * @return the size of the set 234 */ 235 public int size() 236 { 237 return map.size; 238 } 239 240 /** 241 * Helper method which initializes the backing Map. Overridden by 242 * LinkedHashSet for correct semantics. 243 * 244 * @param capacity the initial capacity 245 * @param load the initial load factor 246 * @return the backing HashMap 247 */ 248 HashMap init(int capacity, float load) 249 { 250 return new HashMap(capacity, load); 251 } 252 253 /** 254 * Serializes this object to the given stream. 255 * 256 * @param s the stream to write to 257 * @throws IOException if the underlying stream fails 258 * @serialData the <i>capacity</i> (int) and <i>loadFactor</i> (float) 259 * of the backing store, followed by the set size (int), 260 * then a listing of its elements (Object) in no order 261 */ 262 private void writeObject(ObjectOutputStream s) throws IOException 263 { 264 s.defaultWriteObject(); 265 // Avoid creating intermediate keySet() object by using non-public API. 266 Iterator<T> it = map.iterator(HashMap.KEYS); 267 s.writeInt(map.buckets.length); 268 s.writeFloat(map.loadFactor); 269 s.writeInt(map.size); 270 while (it.hasNext()) 271 s.writeObject(it.next()); 272 } 273 274 /** 275 * Deserializes this object from the given stream. 276 * 277 * @param s the stream to read from 278 * @throws ClassNotFoundException if the underlying stream fails 279 * @throws IOException if the underlying stream fails 280 * @serialData the <i>capacity</i> (int) and <i>loadFactor</i> (float) 281 * of the backing store, followed by the set size (int), 282 * then a listing of its elements (Object) in no order 283 */ 284 private void readObject(ObjectInputStream s) 285 throws IOException, ClassNotFoundException 286 { 287 s.defaultReadObject(); 288 289 map = init(s.readInt(), s.readFloat()); 290 for (int size = s.readInt(); size > 0; size--) 291 map.put((T) s.readObject(), ""); 292 } 293}