J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.util; |
| 27 | |
| 28 | /** |
| 29 | * This class implements the <tt>Set</tt> interface, backed by a hash table |
| 30 | * (actually a <tt>HashMap</tt> instance). It makes no guarantees as to the |
| 31 | * iteration order of the set; in particular, it does not guarantee that the |
| 32 | * order will remain constant over time. This class permits the <tt>null</tt> |
| 33 | * element. |
| 34 | * |
| 35 | * <p>This class offers constant time performance for the basic operations |
| 36 | * (<tt>add</tt>, <tt>remove</tt>, <tt>contains</tt> and <tt>size</tt>), |
| 37 | * assuming the hash function disperses the elements properly among the |
| 38 | * buckets. Iterating over this set requires time proportional to the sum of |
| 39 | * the <tt>HashSet</tt> instance's size (the number of elements) plus the |
| 40 | * "capacity" of the backing <tt>HashMap</tt> instance (the number of |
| 41 | * buckets). Thus, it's very important not to set the initial capacity too |
| 42 | * high (or the load factor too low) if iteration performance is important. |
| 43 | * |
| 44 | * <p><strong>Note that this implementation is not synchronized.</strong> |
| 45 | * If multiple threads access a hash set concurrently, and at least one of |
| 46 | * the threads modifies the set, it <i>must</i> be synchronized externally. |
| 47 | * This is typically accomplished by synchronizing on some object that |
| 48 | * naturally encapsulates the set. |
| 49 | * |
| 50 | * If no such object exists, the set should be "wrapped" using the |
| 51 | * {@link Collections#synchronizedSet Collections.synchronizedSet} |
| 52 | * method. This is best done at creation time, to prevent accidental |
| 53 | * unsynchronized access to the set:<pre> |
| 54 | * Set s = Collections.synchronizedSet(new HashSet(...));</pre> |
| 55 | * |
| 56 | * <p>The iterators returned by this class's <tt>iterator</tt> method are |
| 57 | * <i>fail-fast</i>: if the set is modified at any time after the iterator is |
| 58 | * created, in any way except through the iterator's own <tt>remove</tt> |
| 59 | * method, the Iterator throws a {@link ConcurrentModificationException}. |
| 60 | * Thus, in the face of concurrent modification, the iterator fails quickly |
| 61 | * and cleanly, rather than risking arbitrary, non-deterministic behavior at |
| 62 | * an undetermined time in the future. |
| 63 | * |
| 64 | * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
| 65 | * as it is, generally speaking, impossible to make any hard guarantees in the |
| 66 | * presence of unsynchronized concurrent modification. Fail-fast iterators |
| 67 | * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
| 68 | * Therefore, it would be wrong to write a program that depended on this |
| 69 | * exception for its correctness: <i>the fail-fast behavior of iterators |
| 70 | * should be used only to detect bugs.</i> |
| 71 | * |
| 72 | * <p>This class is a member of the |
| 73 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 74 | * Java Collections Framework</a>. |
| 75 | * |
| 76 | * @param <E> the type of elements maintained by this set |
| 77 | * |
| 78 | * @author Josh Bloch |
| 79 | * @author Neal Gafter |
| 80 | * @see Collection |
| 81 | * @see Set |
| 82 | * @see TreeSet |
| 83 | * @see HashMap |
| 84 | * @since 1.2 |
| 85 | */ |
| 86 | |
| 87 | public class HashSet<E> |
| 88 | extends AbstractSet<E> |
| 89 | implements Set<E>, Cloneable, java.io.Serializable |
| 90 | { |
| 91 | static final long serialVersionUID = -5024744406713321676L; |
| 92 | |
| 93 | private transient HashMap<E,Object> map; |
| 94 | |
| 95 | // Dummy value to associate with an Object in the backing Map |
| 96 | private static final Object PRESENT = new Object(); |
| 97 | |
| 98 | /** |
| 99 | * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has |
| 100 | * default initial capacity (16) and load factor (0.75). |
| 101 | */ |
| 102 | public HashSet() { |
| 103 | map = new HashMap<E,Object>(); |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * Constructs a new set containing the elements in the specified |
| 108 | * collection. The <tt>HashMap</tt> is created with default load factor |
| 109 | * (0.75) and an initial capacity sufficient to contain the elements in |
| 110 | * the specified collection. |
| 111 | * |
| 112 | * @param c the collection whose elements are to be placed into this set |
| 113 | * @throws NullPointerException if the specified collection is null |
| 114 | */ |
| 115 | public HashSet(Collection<? extends E> c) { |
| 116 | map = new HashMap<E,Object>(Math.max((int) (c.size()/.75f) + 1, 16)); |
| 117 | addAll(c); |
| 118 | } |
| 119 | |
| 120 | /** |
| 121 | * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has |
| 122 | * the specified initial capacity and the specified load factor. |
| 123 | * |
| 124 | * @param initialCapacity the initial capacity of the hash map |
| 125 | * @param loadFactor the load factor of the hash map |
| 126 | * @throws IllegalArgumentException if the initial capacity is less |
| 127 | * than zero, or if the load factor is nonpositive |
| 128 | */ |
| 129 | public HashSet(int initialCapacity, float loadFactor) { |
| 130 | map = new HashMap<E,Object>(initialCapacity, loadFactor); |
| 131 | } |
| 132 | |
| 133 | /** |
| 134 | * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has |
| 135 | * the specified initial capacity and default load factor (0.75). |
| 136 | * |
| 137 | * @param initialCapacity the initial capacity of the hash table |
| 138 | * @throws IllegalArgumentException if the initial capacity is less |
| 139 | * than zero |
| 140 | */ |
| 141 | public HashSet(int initialCapacity) { |
| 142 | map = new HashMap<E,Object>(initialCapacity); |
| 143 | } |
| 144 | |
| 145 | /** |
| 146 | * Constructs a new, empty linked hash set. (This package private |
| 147 | * constructor is only used by LinkedHashSet.) The backing |
| 148 | * HashMap instance is a LinkedHashMap with the specified initial |
| 149 | * capacity and the specified load factor. |
| 150 | * |
| 151 | * @param initialCapacity the initial capacity of the hash map |
| 152 | * @param loadFactor the load factor of the hash map |
| 153 | * @param dummy ignored (distinguishes this |
| 154 | * constructor from other int, float constructor.) |
| 155 | * @throws IllegalArgumentException if the initial capacity is less |
| 156 | * than zero, or if the load factor is nonpositive |
| 157 | */ |
| 158 | HashSet(int initialCapacity, float loadFactor, boolean dummy) { |
| 159 | map = new LinkedHashMap<E,Object>(initialCapacity, loadFactor); |
| 160 | } |
| 161 | |
| 162 | /** |
| 163 | * Returns an iterator over the elements in this set. The elements |
| 164 | * are returned in no particular order. |
| 165 | * |
| 166 | * @return an Iterator over the elements in this set |
| 167 | * @see ConcurrentModificationException |
| 168 | */ |
| 169 | public Iterator<E> iterator() { |
| 170 | return map.keySet().iterator(); |
| 171 | } |
| 172 | |
| 173 | /** |
| 174 | * Returns the number of elements in this set (its cardinality). |
| 175 | * |
| 176 | * @return the number of elements in this set (its cardinality) |
| 177 | */ |
| 178 | public int size() { |
| 179 | return map.size(); |
| 180 | } |
| 181 | |
| 182 | /** |
| 183 | * Returns <tt>true</tt> if this set contains no elements. |
| 184 | * |
| 185 | * @return <tt>true</tt> if this set contains no elements |
| 186 | */ |
| 187 | public boolean isEmpty() { |
| 188 | return map.isEmpty(); |
| 189 | } |
| 190 | |
| 191 | /** |
| 192 | * Returns <tt>true</tt> if this set contains the specified element. |
| 193 | * More formally, returns <tt>true</tt> if and only if this set |
| 194 | * contains an element <tt>e</tt> such that |
| 195 | * <tt>(o==null ? e==null : o.equals(e))</tt>. |
| 196 | * |
| 197 | * @param o element whose presence in this set is to be tested |
| 198 | * @return <tt>true</tt> if this set contains the specified element |
| 199 | */ |
| 200 | public boolean contains(Object o) { |
| 201 | return map.containsKey(o); |
| 202 | } |
| 203 | |
| 204 | /** |
| 205 | * Adds the specified element to this set if it is not already present. |
| 206 | * More formally, adds the specified element <tt>e</tt> to this set if |
| 207 | * this set contains no element <tt>e2</tt> such that |
| 208 | * <tt>(e==null ? e2==null : e.equals(e2))</tt>. |
| 209 | * If this set already contains the element, the call leaves the set |
| 210 | * unchanged and returns <tt>false</tt>. |
| 211 | * |
| 212 | * @param e element to be added to this set |
| 213 | * @return <tt>true</tt> if this set did not already contain the specified |
| 214 | * element |
| 215 | */ |
| 216 | public boolean add(E e) { |
| 217 | return map.put(e, PRESENT)==null; |
| 218 | } |
| 219 | |
| 220 | /** |
| 221 | * Removes the specified element from this set if it is present. |
| 222 | * More formally, removes an element <tt>e</tt> such that |
| 223 | * <tt>(o==null ? e==null : o.equals(e))</tt>, |
| 224 | * if this set contains such an element. Returns <tt>true</tt> if |
| 225 | * this set contained the element (or equivalently, if this set |
| 226 | * changed as a result of the call). (This set will not contain the |
| 227 | * element once the call returns.) |
| 228 | * |
| 229 | * @param o object to be removed from this set, if present |
| 230 | * @return <tt>true</tt> if the set contained the specified element |
| 231 | */ |
| 232 | public boolean remove(Object o) { |
| 233 | return map.remove(o)==PRESENT; |
| 234 | } |
| 235 | |
| 236 | /** |
| 237 | * Removes all of the elements from this set. |
| 238 | * The set will be empty after this call returns. |
| 239 | */ |
| 240 | public void clear() { |
| 241 | map.clear(); |
| 242 | } |
| 243 | |
| 244 | /** |
| 245 | * Returns a shallow copy of this <tt>HashSet</tt> instance: the elements |
| 246 | * themselves are not cloned. |
| 247 | * |
| 248 | * @return a shallow copy of this set |
| 249 | */ |
| 250 | public Object clone() { |
| 251 | try { |
| 252 | HashSet<E> newSet = (HashSet<E>) super.clone(); |
| 253 | newSet.map = (HashMap<E, Object>) map.clone(); |
| 254 | return newSet; |
| 255 | } catch (CloneNotSupportedException e) { |
| 256 | throw new InternalError(); |
| 257 | } |
| 258 | } |
| 259 | |
| 260 | /** |
| 261 | * Save the state of this <tt>HashSet</tt> instance to a stream (that is, |
| 262 | * serialize it). |
| 263 | * |
| 264 | * @serialData The capacity of the backing <tt>HashMap</tt> instance |
| 265 | * (int), and its load factor (float) are emitted, followed by |
| 266 | * the size of the set (the number of elements it contains) |
| 267 | * (int), followed by all of its elements (each an Object) in |
| 268 | * no particular order. |
| 269 | */ |
| 270 | private void writeObject(java.io.ObjectOutputStream s) |
| 271 | throws java.io.IOException { |
| 272 | // Write out any hidden serialization magic |
| 273 | s.defaultWriteObject(); |
| 274 | |
| 275 | // Write out HashMap capacity and load factor |
| 276 | s.writeInt(map.capacity()); |
| 277 | s.writeFloat(map.loadFactor()); |
| 278 | |
| 279 | // Write out size |
| 280 | s.writeInt(map.size()); |
| 281 | |
| 282 | // Write out all elements in the proper order. |
| 283 | for (Iterator i=map.keySet().iterator(); i.hasNext(); ) |
| 284 | s.writeObject(i.next()); |
| 285 | } |
| 286 | |
| 287 | /** |
| 288 | * Reconstitute the <tt>HashSet</tt> instance from a stream (that is, |
| 289 | * deserialize it). |
| 290 | */ |
| 291 | private void readObject(java.io.ObjectInputStream s) |
| 292 | throws java.io.IOException, ClassNotFoundException { |
| 293 | // Read in any hidden serialization magic |
| 294 | s.defaultReadObject(); |
| 295 | |
| 296 | // Read in HashMap capacity and load factor and create backing HashMap |
| 297 | int capacity = s.readInt(); |
| 298 | float loadFactor = s.readFloat(); |
| 299 | map = (((HashSet)this) instanceof LinkedHashSet ? |
| 300 | new LinkedHashMap<E,Object>(capacity, loadFactor) : |
| 301 | new HashMap<E,Object>(capacity, loadFactor)); |
| 302 | |
| 303 | // Read in size |
| 304 | int size = s.readInt(); |
| 305 | |
| 306 | // Read in all elements in the proper order. |
| 307 | for (int i=0; i<size; i++) { |
| 308 | E e = (E) s.readObject(); |
| 309 | map.put(e, PRESENT); |
| 310 | } |
| 311 | } |
| 312 | } |