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| 1 | /* | ||
| 2 | * Copyright (c) 1997, 2010, Oracle and/or its affiliates. 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. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * 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<>(); | ||
| 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<>(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<>(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<>(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<>(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 (E e : map.keySet()) | ||
| 284 | s.writeObject(e); | ||
| 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 | } | ||