src/share/classes/java/util/HashMap.java

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rev 5431 : 7126277: Alternative hashing implementation


 158      * @serial
 159      */
 160     int threshold;
 161 
 162     /**
 163      * The load factor for the hash table.
 164      *
 165      * @serial
 166      */
 167     final float loadFactor;
 168 
 169     /**
 170      * The number of times this HashMap has been structurally modified
 171      * Structural modifications are those that change the number of mappings in
 172      * the HashMap or otherwise modify its internal structure (e.g.,
 173      * rehash).  This field is used to make iterators on Collection-views of
 174      * the HashMap fail-fast.  (See ConcurrentModificationException).
 175      */
 176     transient int modCount;
 177 





























 178     /**
 179      * Constructs an empty <tt>HashMap</tt> with the specified initial
 180      * capacity and load factor.
 181      *
 182      * @param  initialCapacity the initial capacity
 183      * @param  loadFactor      the load factor
 184      * @throws IllegalArgumentException if the initial capacity is negative
 185      *         or the load factor is nonpositive
 186      */
 187     public HashMap(int initialCapacity, float loadFactor) {
 188         if (initialCapacity < 0)
 189             throw new IllegalArgumentException("Illegal initial capacity: " +
 190                                                initialCapacity);
 191         if (initialCapacity > MAXIMUM_CAPACITY)
 192             initialCapacity = MAXIMUM_CAPACITY;
 193         if (loadFactor <= 0 || Float.isNaN(loadFactor))
 194             throw new IllegalArgumentException("Illegal load factor: " +
 195                                                loadFactor);
 196 
 197         // Find a power of 2 >= initialCapacity
 198         int capacity = 1;
 199         while (capacity < initialCapacity)
 200             capacity <<= 1;
 201 
 202         this.loadFactor = loadFactor;
 203         threshold = (int)(capacity * loadFactor);
 204         table = new Entry[capacity];
 205         init();
 206     }
 207 
 208     /**
 209      * Constructs an empty <tt>HashMap</tt> with the specified initial
 210      * capacity and the default load factor (0.75).
 211      *
 212      * @param  initialCapacity the initial capacity.
 213      * @throws IllegalArgumentException if the initial capacity is negative.
 214      */
 215     public HashMap(int initialCapacity) {
 216         this(initialCapacity, DEFAULT_LOAD_FACTOR);
 217     }
 218 
 219     /**
 220      * Constructs an empty <tt>HashMap</tt> with the default initial capacity
 221      * (16) and the default load factor (0.75).
 222      */
 223     public HashMap() {
 224         this.loadFactor = DEFAULT_LOAD_FACTOR;
 225         threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
 226         table = new Entry[DEFAULT_INITIAL_CAPACITY];
 227         init();
 228     }
 229 
 230     /**
 231      * Constructs a new <tt>HashMap</tt> with the same mappings as the
 232      * specified <tt>Map</tt>.  The <tt>HashMap</tt> is created with
 233      * default load factor (0.75) and an initial capacity sufficient to
 234      * hold the mappings in the specified <tt>Map</tt>.
 235      *
 236      * @param   m the map whose mappings are to be placed in this map
 237      * @throws  NullPointerException if the specified map is null
 238      */
 239     public HashMap(Map<? extends K, ? extends V> m) {
 240         this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
 241                       DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
 242         putAllForCreate(m);
 243     }
 244 
 245     // internal utilities
 246 
 247     /**
 248      * Initialization hook for subclasses. This method is called
 249      * in all constructors and pseudo-constructors (clone, readObject)
 250      * after HashMap has been initialized but before any entries have
 251      * been inserted.  (In the absence of this method, readObject would
 252      * require explicit knowledge of subclasses.)
 253      */
 254     void init() {
 255     }
 256 
 257     /**
 258      * Applies a supplemental hash function to a given hashCode, which
 259      * defends against poor quality hash functions.  This is critical
 260      * because HashMap uses power-of-two length hash tables, that
 261      * otherwise encounter collisions for hashCodes that do not differ
 262      * in lower bits. Note: Null keys always map to hash 0, thus index 0.
 263      */
 264     static int hash(int h) {







 265         // This function ensures that hashCodes that differ only by
 266         // constant multiples at each bit position have a bounded
 267         // number of collisions (approximately 8 at default load factor).
 268         h ^= (h >>> 20) ^ (h >>> 12);
 269         return h ^ (h >>> 7) ^ (h >>> 4);
 270     }
 271 
 272     /**
 273      * Returns index for hash code h.
 274      */
 275     static int indexFor(int h, int length) {
 276         return h & (length-1);
 277     }
 278 
 279     /**
 280      * Returns the number of key-value mappings in this map.
 281      *
 282      * @return the number of key-value mappings in this map
 283      */
 284     public int size() {


 296 
 297     /**
 298      * Returns the value to which the specified key is mapped,
 299      * or {@code null} if this map contains no mapping for the key.
 300      *
 301      * <p>More formally, if this map contains a mapping from a key
 302      * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
 303      * key.equals(k))}, then this method returns {@code v}; otherwise
 304      * it returns {@code null}.  (There can be at most one such mapping.)
 305      *
 306      * <p>A return value of {@code null} does not <i>necessarily</i>
 307      * indicate that the map contains no mapping for the key; it's also
 308      * possible that the map explicitly maps the key to {@code null}.
 309      * The {@link #containsKey containsKey} operation may be used to
 310      * distinguish these two cases.
 311      *
 312      * @see #put(Object, Object)
 313      */
 314     @SuppressWarnings("unchecked")
 315     public V get(Object key) {
 316         if (key == null)
 317             return (V)getForNullKey();
 318         int hash = hash(key.hashCode());
 319         for (Entry<?,?> e = table[indexFor(hash, table.length)];
 320              e != null;
 321              e = e.next) {
 322             Object k;
 323             if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
 324                 return (V)e.value;
 325         }
 326         return null;
 327     }
 328 
 329     /**
 330      * Offloaded version of get() to look up null keys.  Null keys map
 331      * to index 0.  This null case is split out into separate methods
 332      * for the sake of performance in the two most commonly used
 333      * operations (get and put), but incorporated with conditionals in
 334      * others.
 335      */
 336     private Object getForNullKey() {
 337         for (Entry<?,?> e = table[0]; e != null; e = e.next) {
 338             if (e.key == null)
 339                 return e.value;
 340         }
 341         return null;
 342     }
 343 
 344     /**
 345      * Returns <tt>true</tt> if this map contains a mapping for the
 346      * specified key.
 347      *
 348      * @param   key   The key whose presence in this map is to be tested
 349      * @return <tt>true</tt> if this map contains a mapping for the specified
 350      * key.
 351      */
 352     public boolean containsKey(Object key) {
 353         return getEntry(key) != null;
 354     }
 355 
 356     /**
 357      * Returns the entry associated with the specified key in the
 358      * HashMap.  Returns null if the HashMap contains no mapping
 359      * for the key.
 360      */
 361     @SuppressWarnings("unchecked")
 362     final Entry<K,V> getEntry(Object key) {
 363         int hash = (key == null) ? 0 : hash(key.hashCode());
 364         for (Entry<?,?> e = table[indexFor(hash, table.length)];
 365              e != null;
 366              e = e.next) {
 367             Object k;
 368             if (e.hash == hash &&
 369                 ((k = e.key) == key || (key != null && key.equals(k))))
 370                 return (Entry<K,V>)e;
 371         }
 372         return null;
 373     }
 374 
 375 
 376     /**
 377      * Associates the specified value with the specified key in this map.
 378      * If the map previously contained a mapping for the key, the old
 379      * value is replaced.
 380      *
 381      * @param key key with which the specified value is to be associated
 382      * @param value value to be associated with the specified key
 383      * @return the previous value associated with <tt>key</tt>, or
 384      *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
 385      *         (A <tt>null</tt> return can also indicate that the map
 386      *         previously associated <tt>null</tt> with <tt>key</tt>.)
 387      */
 388     public V put(K key, V value) {
 389         if (key == null)
 390             return putForNullKey(value);
 391         int hash = hash(key.hashCode());
 392         int i = indexFor(hash, table.length);
 393         @SuppressWarnings("unchecked")
 394         Entry<K,V> e = (Entry<K,V>)table[i];
 395         for(; e != null; e = e.next) {
 396             Object k;
 397             if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
 398                 V oldValue = e.value;
 399                 e.value = value;
 400                 e.recordAccess(this);
 401                 return oldValue;
 402             }
 403         }
 404 
 405         modCount++;
 406         addEntry(hash, key, value, i);
 407         return null;
 408     }
 409 
 410     /**
 411      * Offloaded version of put for null keys


 416         for(; e != null; e = e.next) {
 417             if (e.key == null) {
 418                 V oldValue = e.value;
 419                 e.value = value;
 420                 e.recordAccess(this);
 421                 return oldValue;
 422             }
 423         }
 424         modCount++;
 425         addEntry(0, null, value, 0);
 426         return null;
 427     }
 428 
 429     /**
 430      * This method is used instead of put by constructors and
 431      * pseudoconstructors (clone, readObject).  It does not resize the table,
 432      * check for comodification, etc.  It calls createEntry rather than
 433      * addEntry.
 434      */
 435     private void putForCreate(K key, V value) {
 436         int hash = (key == null) ? 0 : hash(key.hashCode());
 437         int i = indexFor(hash, table.length);
 438 
 439         /**
 440          * Look for preexisting entry for key.  This will never happen for
 441          * clone or deserialize.  It will only happen for construction if the
 442          * input Map is a sorted map whose ordering is inconsistent w/ equals.
 443          */
 444         for (@SuppressWarnings("unchecked")
 445              Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) {
 446             Object k;
 447             if (e.hash == hash &&
 448                 ((k = e.key) == key || (key != null && key.equals(k)))) {
 449                 e.value = value;
 450                 return;
 451             }
 452         }
 453 
 454         createEntry(hash, key, value, i);
 455     }
 456 


 467      * If current capacity is MAXIMUM_CAPACITY, this method does not
 468      * resize the map, but sets threshold to Integer.MAX_VALUE.
 469      * This has the effect of preventing future calls.
 470      *
 471      * @param newCapacity the new capacity, MUST be a power of two;
 472      *        must be greater than current capacity unless current
 473      *        capacity is MAXIMUM_CAPACITY (in which case value
 474      *        is irrelevant).
 475      */
 476     void resize(int newCapacity) {
 477         Entry<?,?>[] oldTable = table;
 478         int oldCapacity = oldTable.length;
 479         if (oldCapacity == MAXIMUM_CAPACITY) {
 480             threshold = Integer.MAX_VALUE;
 481             return;
 482         }
 483 
 484         Entry<?,?>[] newTable = new Entry<?,?>[newCapacity];
 485         transfer(newTable);
 486         table = newTable;
 487         threshold = (int)(newCapacity * loadFactor);
 488     }
 489 
 490     /**
 491      * Transfers all entries from current table to newTable.
 492      */
 493     @SuppressWarnings("unchecked")
 494     void transfer(Entry<?,?>[] newTable) {
 495         Entry<?,?>[] src = table;
 496         int newCapacity = newTable.length;
 497         for (int j = 0; j < src.length; j++) {
 498             Entry<K,V> e = (Entry<K,V>)src[j];
 499             if (e != null) {
 500                 src[j] = null;
 501                 do {
 502                     Entry<K,V> next = e.next;
 503                     int i = indexFor(e.hash, newCapacity);
 504                     e.next = (Entry<K,V>)newTable[i];
 505                     newTable[i] = e;
 506                     e = next;
 507                 } while (e != null);
 508             }
 509         }

 510     }
 511 
 512     /**
 513      * Copies all of the mappings from the specified map to this map.
 514      * These mappings will replace any mappings that this map had for
 515      * any of the keys currently in the specified map.
 516      *
 517      * @param m mappings to be stored in this map
 518      * @throws NullPointerException if the specified map is null
 519      */
 520     public void putAll(Map<? extends K, ? extends V> m) {
 521         int numKeysToBeAdded = m.size();
 522         if (numKeysToBeAdded == 0)
 523             return;
 524 
 525         /*
 526          * Expand the map if the map if the number of mappings to be added
 527          * is greater than or equal to threshold.  This is conservative; the
 528          * obvious condition is (m.size() + size) >= threshold, but this
 529          * condition could result in a map with twice the appropriate capacity,


 549     /**
 550      * Removes the mapping for the specified key from this map if present.
 551      *
 552      * @param  key key whose mapping is to be removed from the map
 553      * @return the previous value associated with <tt>key</tt>, or
 554      *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
 555      *         (A <tt>null</tt> return can also indicate that the map
 556      *         previously associated <tt>null</tt> with <tt>key</tt>.)
 557      */
 558     public V remove(Object key) {
 559         Entry<K,V> e = removeEntryForKey(key);
 560         return (e == null ? null : e.value);
 561     }
 562 
 563     /**
 564      * Removes and returns the entry associated with the specified key
 565      * in the HashMap.  Returns null if the HashMap contains no mapping
 566      * for this key.
 567      */
 568     final Entry<K,V> removeEntryForKey(Object key) {
 569         int hash = (key == null) ? 0 : hash(key.hashCode());
 570         int i = indexFor(hash, table.length);
 571         @SuppressWarnings("unchecked")
 572             Entry<K,V> prev = (Entry<K,V>)table[i];
 573         Entry<K,V> e = prev;
 574 
 575         while (e != null) {
 576             Entry<K,V> next = e.next;
 577             Object k;
 578             if (e.hash == hash &&
 579                 ((k = e.key) == key || (key != null && key.equals(k)))) {
 580                 modCount++;
 581                 size--;
 582                 if (prev == e)
 583                     table[i] = next;
 584                 else
 585                     prev.next = next;
 586                 e.recordRemoval(this);
 587                 return e;
 588             }
 589             prev = e;
 590             e = next;
 591         }
 592 
 593         return e;
 594     }
 595 
 596     /**
 597      * Special version of remove for EntrySet.

 598      */
 599     final Entry<K,V> removeMapping(Object o) {
 600         if (!(o instanceof Map.Entry))
 601             return null;
 602 
 603         Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
 604         Object key = entry.getKey();
 605         int hash = (key == null) ? 0 : hash(key.hashCode());
 606         int i = indexFor(hash, table.length);
 607         @SuppressWarnings("unchecked")
 608             Entry<K,V> prev = (Entry<K,V>)table[i];
 609         Entry<K,V> e = prev;
 610 
 611         while (e != null) {
 612             Entry<K,V> next = e.next;
 613             if (e.hash == hash && e.equals(entry)) {
 614                 modCount++;
 615                 size--;
 616                 if (prev == e)
 617                     table[i] = next;


 756          */
 757         void recordAccess(HashMap<K,V> m) {
 758         }
 759 
 760         /**
 761          * This method is invoked whenever the entry is
 762          * removed from the table.
 763          */
 764         void recordRemoval(HashMap<K,V> m) {
 765         }
 766     }
 767 
 768     /**
 769      * Adds a new entry with the specified key, value and hash code to
 770      * the specified bucket.  It is the responsibility of this
 771      * method to resize the table if appropriate.
 772      *
 773      * Subclass overrides this to alter the behavior of put method.
 774      */
 775     void addEntry(int hash, K key, V value, int bucketIndex) {
 776         @SuppressWarnings("unchecked")
 777             Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
 778         table[bucketIndex] = new Entry<>(hash, key, value, e);
 779         if (size++ >= threshold)
 780             resize(2 * table.length);





 781     }
 782 
 783     /**
 784      * Like addEntry except that this version is used when creating entries
 785      * as part of Map construction or "pseudo-construction" (cloning,
 786      * deserialization).  This version needn't worry about resizing the table.
 787      *
 788      * Subclass overrides this to alter the behavior of HashMap(Map),
 789      * clone, and readObject.
 790      */
 791     void createEntry(int hash, K key, V value, int bucketIndex) {
 792         @SuppressWarnings("unchecked")
 793             Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
 794         table[bucketIndex] = new Entry<>(hash, key, value, e);
 795         size++;
 796     }
 797 
 798     private abstract class HashIterator<E> implements Iterator<E> {
 799         Entry<?,?> next;        // next entry to return
 800         int expectedModCount;   // For fast-fail


 824 
 825             if ((next = e.next) == null) {
 826                 Entry<?,?>[] t = table;
 827                 while (index < t.length && (next = t[index++]) == null)
 828                     ;
 829             }
 830             current = e;
 831             return (Entry<K,V>)e;
 832         }
 833 
 834         public void remove() {
 835             if (current == null)
 836                 throw new IllegalStateException();
 837             if (modCount != expectedModCount)
 838                 throw new ConcurrentModificationException();
 839             Object k = current.key;
 840             current = null;
 841             HashMap.this.removeEntryForKey(k);
 842             expectedModCount = modCount;
 843         }
 844 
 845     }
 846 
 847     private final class ValueIterator extends HashIterator<V> {
 848         public V next() {
 849             return nextEntry().value;
 850         }
 851     }
 852 
 853     private final class KeyIterator extends HashIterator<K> {
 854         public K next() {
 855             return nextEntry().getKey();
 856         }
 857     }
 858 
 859     private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
 860         public Map.Entry<K,V> next() {
 861             return nextEntry();
 862         }
 863     }
 864 


1004      *             mappings), followed by the key (Object) and value (Object)
1005      *             for each key-value mapping.  The key-value mappings are
1006      *             emitted in no particular order.
1007      */
1008     private void writeObject(java.io.ObjectOutputStream s)
1009         throws IOException
1010     {
1011         Iterator<Map.Entry<K,V>> i =
1012             (size > 0) ? entrySet0().iterator() : null;
1013 
1014         // Write out the threshold, loadfactor, and any hidden stuff
1015         s.defaultWriteObject();
1016 
1017         // Write out number of buckets
1018         s.writeInt(table.length);
1019 
1020         // Write out size (number of Mappings)
1021         s.writeInt(size);
1022 
1023         // Write out keys and values (alternating)
1024         if (i != null) {
1025             while (i.hasNext()) {
1026                 Map.Entry<K,V> e = i.next();
1027                 s.writeObject(e.getKey());
1028                 s.writeObject(e.getValue());
1029             }
1030         }
1031     }
1032 
1033     private static final long serialVersionUID = 362498820763181265L;
1034 
1035     /**
1036      * Reconstitute the <tt>HashMap</tt> instance from a stream (i.e.,
1037      * deserialize it).
1038      */
1039     private void readObject(java.io.ObjectInputStream s)
1040          throws IOException, ClassNotFoundException
1041     {
1042         // Read in the threshold, loadfactor, and any hidden stuff
1043         s.defaultReadObject();







1044 
1045         // Read in number of buckets and allocate the bucket array;
1046         int numBuckets = s.readInt();
1047         table = new Entry[numBuckets];
1048 




















1049         init();  // Give subclass a chance to do its thing.
1050 
1051         // Read in size (number of Mappings)
1052         int size = s.readInt();
1053 
1054         // Read the keys and values, and put the mappings in the HashMap
1055         for (int i=0; i<size; i++) {
1056             @SuppressWarnings("unchecked")
1057                 K key = (K) s.readObject();
1058             @SuppressWarnings("unchecked")
1059                 V value = (V) s.readObject();
1060             putForCreate(key, value);
1061         }
1062     }
1063 
1064     // These methods are used when serializing HashSets
1065     int   capacity()     { return table.length; }
1066     float loadFactor()   { return loadFactor;   }
1067 }


 158      * @serial
 159      */
 160     int threshold;
 161 
 162     /**
 163      * The load factor for the hash table.
 164      *
 165      * @serial
 166      */
 167     final float loadFactor;
 168 
 169     /**
 170      * The number of times this HashMap has been structurally modified
 171      * Structural modifications are those that change the number of mappings in
 172      * the HashMap or otherwise modify its internal structure (e.g.,
 173      * rehash).  This field is used to make iterators on Collection-views of
 174      * the HashMap fail-fast.  (See ConcurrentModificationException).
 175      */
 176     transient int modCount;
 177     
 178     private static class Holder {
 179          /**
 180          * 
 181          */
 182         static final sun.misc.Unsafe UNSAFE;
 183         
 184         /**
 185          * Offset of "final" hashSeed field we must set in
 186          * readObject() method.
 187          */
 188         static final long HASHSEED_OFFSET;
 189 
 190         static {            
 191             try {
 192                 UNSAFE = sun.misc.Unsafe.getUnsafe();
 193                 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
 194                     HashMap.class.getDeclaredField("hashSeed"));                        
 195             } catch (NoSuchFieldException | SecurityException e) {
 196                 throw new InternalError("Failed to record hashSeed offset", e);
 197             }
 198         }
 199     }
 200     
 201     /**
 202      * A randomizing value associated with this instance that is applied to  
 203      * hash code of keys to make hash collisions harder to find.
 204      */
 205     transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
 206 
 207     /**
 208      * Constructs an empty <tt>HashMap</tt> with the specified initial
 209      * capacity and load factor.
 210      *
 211      * @param  initialCapacity the initial capacity
 212      * @param  loadFactor      the load factor
 213      * @throws IllegalArgumentException if the initial capacity is negative
 214      *         or the load factor is nonpositive
 215      */
 216     public HashMap(int initialCapacity, float loadFactor) {
 217         if (initialCapacity < 0)
 218             throw new IllegalArgumentException("Illegal initial capacity: " +
 219                                                initialCapacity);
 220         if (initialCapacity > MAXIMUM_CAPACITY)
 221             initialCapacity = MAXIMUM_CAPACITY;
 222         if (loadFactor <= 0 || Float.isNaN(loadFactor))
 223             throw new IllegalArgumentException("Illegal load factor: " +
 224                                                loadFactor);
 225 
 226         // Find a power of 2 >= initialCapacity
 227         int capacity = 1;
 228         while (capacity < initialCapacity)
 229             capacity <<= 1;
 230 
 231         this.loadFactor = loadFactor;
 232         threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
 233         table = new Entry[capacity];
 234         init();
 235     }
 236 
 237     /**
 238      * Constructs an empty <tt>HashMap</tt> with the specified initial
 239      * capacity and the default load factor (0.75).
 240      *
 241      * @param  initialCapacity the initial capacity.
 242      * @throws IllegalArgumentException if the initial capacity is negative.
 243      */
 244     public HashMap(int initialCapacity) {
 245         this(initialCapacity, DEFAULT_LOAD_FACTOR);
 246     }
 247 
 248     /**
 249      * Constructs an empty <tt>HashMap</tt> with the default initial capacity
 250      * (16) and the default load factor (0.75).
 251      */
 252     public HashMap() {
 253         this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);



 254     }
 255 
 256     /**
 257      * Constructs a new <tt>HashMap</tt> with the same mappings as the
 258      * specified <tt>Map</tt>.  The <tt>HashMap</tt> is created with
 259      * default load factor (0.75) and an initial capacity sufficient to
 260      * hold the mappings in the specified <tt>Map</tt>.
 261      *
 262      * @param   m the map whose mappings are to be placed in this map
 263      * @throws  NullPointerException if the specified map is null
 264      */
 265     public HashMap(Map<? extends K, ? extends V> m) {
 266         this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
 267                       DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
 268         putAllForCreate(m);
 269     }
 270 
 271     // internal utilities
 272 
 273     /**
 274      * Initialization hook for subclasses. This method is called
 275      * in all constructors and pseudo-constructors (clone, readObject)
 276      * after HashMap has been initialized but before any entries have
 277      * been inserted.  (In the absence of this method, readObject would
 278      * require explicit knowledge of subclasses.)
 279      */
 280     void init() {
 281     }
 282 
 283     /**
 284      * Retrieve object hash code and applies a supplemental hash function to the 
 285      * result hash, which defends against poor quality hash functions.  This is 
 286      * critical because HashMap uses power-of-two length hash tables, that
 287      * otherwise encounter collisions for hashCodes that do not differ
 288      * in lower bits.
 289      */
 290     final int hash(Object k) {
 291         int h = hashSeed;
 292         if (k instanceof String) {
 293             return ((String)k).hash32();
 294         }
 295 
 296         h ^= k.hashCode();
 297         
 298         // This function ensures that hashCodes that differ only by
 299         // constant multiples at each bit position have a bounded
 300         // number of collisions (approximately 8 at default load factor).
 301         h ^= (h >>> 20) ^ (h >>> 12);
 302         return h ^ (h >>> 7) ^ (h >>> 4);
 303     }
 304 
 305     /**
 306      * Returns index for hash code h.
 307      */
 308     static int indexFor(int h, int length) {
 309         return h & (length-1);
 310     }
 311 
 312     /**
 313      * Returns the number of key-value mappings in this map.
 314      *
 315      * @return the number of key-value mappings in this map
 316      */
 317     public int size() {


 329 
 330     /**
 331      * Returns the value to which the specified key is mapped,
 332      * or {@code null} if this map contains no mapping for the key.
 333      *
 334      * <p>More formally, if this map contains a mapping from a key
 335      * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
 336      * key.equals(k))}, then this method returns {@code v}; otherwise
 337      * it returns {@code null}.  (There can be at most one such mapping.)
 338      *
 339      * <p>A return value of {@code null} does not <i>necessarily</i>
 340      * indicate that the map contains no mapping for the key; it's also
 341      * possible that the map explicitly maps the key to {@code null}.
 342      * The {@link #containsKey containsKey} operation may be used to
 343      * distinguish these two cases.
 344      *
 345      * @see #put(Object, Object)
 346      */
 347     @SuppressWarnings("unchecked")
 348     public V get(Object key) {
 349         Entry<K,V> entry = getEntry(key);











 350         
 351         return null == entry ? null : entry.getValue();












 352     }
 353 
 354     /**
 355      * Returns <tt>true</tt> if this map contains a mapping for the
 356      * specified key.
 357      *
 358      * @param   key   The key whose presence in this map is to be tested
 359      * @return <tt>true</tt> if this map contains a mapping for the specified
 360      * key.
 361      */
 362     public boolean containsKey(Object key) {
 363         return getEntry(key) != null;
 364     }
 365 
 366     /**
 367      * Returns the entry associated with the specified key in the
 368      * HashMap.  Returns null if the HashMap contains no mapping
 369      * for the key.
 370      */
 371     @SuppressWarnings("unchecked")
 372     final Entry<K,V> getEntry(Object key) {
 373         int hash = (key == null) ? 0 : hash(key);
 374         for (Entry<?,?> e = table[indexFor(hash, table.length)];
 375              e != null;
 376              e = e.next) {
 377             Object k;
 378             if (e.hash == hash &&
 379                 ((k = e.key) == key || (key != null && key.equals(k))))
 380                 return (Entry<K,V>)e;
 381         }
 382         return null;
 383     }
 384 
 385 
 386     /**
 387      * Associates the specified value with the specified key in this map.
 388      * If the map previously contained a mapping for the key, the old
 389      * value is replaced.
 390      *
 391      * @param key key with which the specified value is to be associated
 392      * @param value value to be associated with the specified key
 393      * @return the previous value associated with <tt>key</tt>, or
 394      *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
 395      *         (A <tt>null</tt> return can also indicate that the map
 396      *         previously associated <tt>null</tt> with <tt>key</tt>.)
 397      */
 398     public V put(K key, V value) {
 399         if (key == null)
 400             return putForNullKey(value);
 401         int hash = hash(key);
 402         int i = indexFor(hash, table.length);
 403         @SuppressWarnings("unchecked")
 404         Entry<K,V> e = (Entry<K,V>)table[i];
 405         for(; e != null; e = e.next) {
 406             Object k;
 407             if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
 408                 V oldValue = e.value;
 409                 e.value = value;
 410                 e.recordAccess(this);
 411                 return oldValue;
 412             }
 413         }
 414 
 415         modCount++;
 416         addEntry(hash, key, value, i);
 417         return null;
 418     }
 419 
 420     /**
 421      * Offloaded version of put for null keys


 426         for(; e != null; e = e.next) {
 427             if (e.key == null) {
 428                 V oldValue = e.value;
 429                 e.value = value;
 430                 e.recordAccess(this);
 431                 return oldValue;
 432             }
 433         }
 434         modCount++;
 435         addEntry(0, null, value, 0);
 436         return null;
 437     }
 438 
 439     /**
 440      * This method is used instead of put by constructors and
 441      * pseudoconstructors (clone, readObject).  It does not resize the table,
 442      * check for comodification, etc.  It calls createEntry rather than
 443      * addEntry.
 444      */
 445     private void putForCreate(K key, V value) {
 446         int hash = null == key ? 0 : hash(key);
 447         int i = indexFor(hash, table.length);
 448 
 449         /**
 450          * Look for preexisting entry for key.  This will never happen for
 451          * clone or deserialize.  It will only happen for construction if the
 452          * input Map is a sorted map whose ordering is inconsistent w/ equals.
 453          */
 454         for (@SuppressWarnings("unchecked")
 455              Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) {
 456             Object k;
 457             if (e.hash == hash &&
 458                 ((k = e.key) == key || (key != null && key.equals(k)))) {
 459                 e.value = value;
 460                 return;
 461             }
 462         }
 463 
 464         createEntry(hash, key, value, i);
 465     }
 466 


 477      * If current capacity is MAXIMUM_CAPACITY, this method does not
 478      * resize the map, but sets threshold to Integer.MAX_VALUE.
 479      * This has the effect of preventing future calls.
 480      *
 481      * @param newCapacity the new capacity, MUST be a power of two;
 482      *        must be greater than current capacity unless current
 483      *        capacity is MAXIMUM_CAPACITY (in which case value
 484      *        is irrelevant).
 485      */
 486     void resize(int newCapacity) {
 487         Entry<?,?>[] oldTable = table;
 488         int oldCapacity = oldTable.length;
 489         if (oldCapacity == MAXIMUM_CAPACITY) {
 490             threshold = Integer.MAX_VALUE;
 491             return;
 492         }
 493 
 494         Entry<?,?>[] newTable = new Entry<?,?>[newCapacity];
 495         transfer(newTable);
 496         table = newTable;
 497         threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
 498     }
 499 
 500     /**
 501      * Transfers all entries from current table to newTable.
 502      */
 503     @SuppressWarnings("unchecked")
 504     void transfer(Entry<?,?>[] newTable) {
 505         Entry<?,?>[] src = table;
 506         int newCapacity = newTable.length;
 507         for (int j = 0; j < src.length; j++ ) {
 508             Entry<K,V> e = (Entry<K,V>) src[j];
 509             while(null != e) {


 510                 Entry<K,V> next = e.next;
 511                 int i = indexFor(e.hash, newCapacity);
 512                 e.next = (Entry<K,V>) newTable[i];
 513                 newTable[i] = e;
 514                 e = next;

 515             }
 516         }
 517         Arrays.fill(table, null);
 518     }
 519 
 520     /**
 521      * Copies all of the mappings from the specified map to this map.
 522      * These mappings will replace any mappings that this map had for
 523      * any of the keys currently in the specified map.
 524      *
 525      * @param m mappings to be stored in this map
 526      * @throws NullPointerException if the specified map is null
 527      */
 528     public void putAll(Map<? extends K, ? extends V> m) {
 529         int numKeysToBeAdded = m.size();
 530         if (numKeysToBeAdded == 0)
 531             return;
 532 
 533         /*
 534          * Expand the map if the map if the number of mappings to be added
 535          * is greater than or equal to threshold.  This is conservative; the
 536          * obvious condition is (m.size() + size) >= threshold, but this
 537          * condition could result in a map with twice the appropriate capacity,


 557     /**
 558      * Removes the mapping for the specified key from this map if present.
 559      *
 560      * @param  key key whose mapping is to be removed from the map
 561      * @return the previous value associated with <tt>key</tt>, or
 562      *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
 563      *         (A <tt>null</tt> return can also indicate that the map
 564      *         previously associated <tt>null</tt> with <tt>key</tt>.)
 565      */
 566     public V remove(Object key) {
 567         Entry<K,V> e = removeEntryForKey(key);
 568         return (e == null ? null : e.value);
 569     }
 570 
 571     /**
 572      * Removes and returns the entry associated with the specified key
 573      * in the HashMap.  Returns null if the HashMap contains no mapping
 574      * for this key.
 575      */
 576     final Entry<K,V> removeEntryForKey(Object key) {
 577         int hash = (key == null) ? 0 : hash(key);
 578         int i = indexFor(hash, table.length);
 579         @SuppressWarnings("unchecked")
 580             Entry<K,V> prev = (Entry<K,V>)table[i];
 581         Entry<K,V> e = prev;
 582 
 583         while (e != null) {
 584             Entry<K,V> next = e.next;
 585             Object k;
 586             if (e.hash == hash &&
 587                 ((k = e.key) == key || (key != null && key.equals(k)))) {
 588                 modCount++;
 589                 size--;
 590                 if (prev == e)
 591                     table[i] = next;
 592                 else
 593                     prev.next = next;
 594                 e.recordRemoval(this);
 595                 return e;
 596             }
 597             prev = e;
 598             e = next;
 599         }
 600 
 601         return e;
 602     }
 603 
 604     /**
 605      * Special version of remove for EntrySet using {@code Map.Entry.equals()}
 606      * for matching.
 607      */
 608     final Entry<K,V> removeMapping(Object o) {
 609         if (!(o instanceof Map.Entry))
 610             return null;
 611 
 612         Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
 613         Object key = entry.getKey();
 614         int hash = (key == null) ? 0 : hash(key.hashCode());
 615         int i = indexFor(hash, table.length);
 616         @SuppressWarnings("unchecked")
 617             Entry<K,V> prev = (Entry<K,V>)table[i];
 618         Entry<K,V> e = prev;
 619 
 620         while (e != null) {
 621             Entry<K,V> next = e.next;
 622             if (e.hash == hash && e.equals(entry)) {
 623                 modCount++;
 624                 size--;
 625                 if (prev == e)
 626                     table[i] = next;


 765          */
 766         void recordAccess(HashMap<K,V> m) {
 767         }
 768 
 769         /**
 770          * This method is invoked whenever the entry is
 771          * removed from the table.
 772          */
 773         void recordRemoval(HashMap<K,V> m) {
 774         }
 775     }
 776 
 777     /**
 778      * Adds a new entry with the specified key, value and hash code to
 779      * the specified bucket.  It is the responsibility of this
 780      * method to resize the table if appropriate.
 781      *
 782      * Subclass overrides this to alter the behavior of put method.
 783      */
 784     void addEntry(int hash, K key, V value, int bucketIndex) {
 785         if ((size >= threshold) && (null != table[bucketIndex])) {



 786             resize(2 * table.length);
 787             hash = hash(key);
 788             bucketIndex = indexFor(hash, table.length);
 789         }
 790         
 791         createEntry(hash, key, value, bucketIndex);
 792     }
 793 
 794     /**
 795      * Like addEntry except that this version is used when creating entries
 796      * as part of Map construction or "pseudo-construction" (cloning,
 797      * deserialization).  This version needn't worry about resizing the table.
 798      *
 799      * Subclass overrides this to alter the behavior of HashMap(Map),
 800      * clone, and readObject.
 801      */
 802     void createEntry(int hash, K key, V value, int bucketIndex) {
 803         @SuppressWarnings("unchecked")
 804             Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
 805         table[bucketIndex] = new Entry<>(hash, key, value, e);
 806         size++;
 807     }
 808 
 809     private abstract class HashIterator<E> implements Iterator<E> {
 810         Entry<?,?> next;        // next entry to return
 811         int expectedModCount;   // For fast-fail


 835 
 836             if ((next = e.next) == null) {
 837                 Entry<?,?>[] t = table;
 838                 while (index < t.length && (next = t[index++]) == null)
 839                     ;
 840             }
 841             current = e;
 842             return (Entry<K,V>)e;
 843         }
 844 
 845         public void remove() {
 846             if (current == null)
 847                 throw new IllegalStateException();
 848             if (modCount != expectedModCount)
 849                 throw new ConcurrentModificationException();
 850             Object k = current.key;
 851             current = null;
 852             HashMap.this.removeEntryForKey(k);
 853             expectedModCount = modCount;
 854         }

 855     }
 856 
 857     private final class ValueIterator extends HashIterator<V> {
 858         public V next() {
 859             return nextEntry().value;
 860         }
 861     }
 862 
 863     private final class KeyIterator extends HashIterator<K> {
 864         public K next() {
 865             return nextEntry().getKey();
 866         }
 867     }
 868 
 869     private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
 870         public Map.Entry<K,V> next() {
 871             return nextEntry();
 872         }
 873     }
 874 


1014      *             mappings), followed by the key (Object) and value (Object)
1015      *             for each key-value mapping.  The key-value mappings are
1016      *             emitted in no particular order.
1017      */
1018     private void writeObject(java.io.ObjectOutputStream s)
1019         throws IOException
1020     {
1021         Iterator<Map.Entry<K,V>> i =
1022             (size > 0) ? entrySet0().iterator() : null;
1023 
1024         // Write out the threshold, loadfactor, and any hidden stuff
1025         s.defaultWriteObject();
1026 
1027         // Write out number of buckets
1028         s.writeInt(table.length);
1029 
1030         // Write out size (number of Mappings)
1031         s.writeInt(size);
1032 
1033         // Write out keys and values (alternating)
1034         if (size > 0) {
1035             for(Map.Entry<K,V> e : entrySet0()) {

1036                 s.writeObject(e.getKey());
1037                 s.writeObject(e.getValue());
1038             }
1039         }
1040     }
1041 
1042     private static final long serialVersionUID = 362498820763181265L;
1043 
1044     /**
1045      * Reconstitute the {@code HashMap} instance from a stream (i.e.,
1046      * deserialize it).
1047      */
1048     private void readObject(java.io.ObjectInputStream s)
1049          throws IOException, ClassNotFoundException
1050     {
1051         // Read in the threshold (ignored), loadfactor, and any hidden stuff
1052         s.defaultReadObject();
1053         if (loadFactor <= 0 || Float.isNaN(loadFactor))
1054             throw new InvalidObjectException("Illegal load factor: " +
1055                                                loadFactor);
1056                 
1057         // set hashMask
1058         Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET, 
1059                 sun.misc.Hashing.randomHashSeed(this));
1060         
1061         // Read in number of buckets and allocate the bucket array;
1062         s.readInt(); // ignored

1063 
1064         // Read number of mappings
1065         int mappings = s.readInt();
1066         if (mappings < 0)
1067             throw new InvalidObjectException("Illegal mappings count: " +
1068                                                mappings);
1069         
1070         int initialCapacity = (int) Math.min(
1071                 // capacity chosen by number of mappings 
1072                 // and desired load (if >= 0.25)
1073                 mappings * Math.min(1 / loadFactor, 4.0f),
1074                 // we have limits...
1075                 HashMap.MAXIMUM_CAPACITY);
1076         int capacity = 1;
1077         // find smallest power of two which holds all mappings
1078         while (capacity < initialCapacity) {
1079             capacity <<= 1;
1080         }
1081         
1082         table = new Entry[capacity];
1083         threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);        
1084         init();  // Give subclass a chance to do its thing.
1085 


1086 
1087         // Read the keys and values, and put the mappings in the HashMap
1088         for (int i=0; i<mappings; i++) {
1089             @SuppressWarnings("unchecked")
1090                 K key = (K) s.readObject();
1091             @SuppressWarnings("unchecked")
1092                 V value = (V) s.readObject();
1093             putForCreate(key, value);
1094         }
1095     }
1096 
1097     // These methods are used when serializing HashSets
1098     int   capacity()     { return table.length; }
1099     float loadFactor()   { return loadFactor;   }
1100 }