rev 6845 : 80111200: (coll) Optimize empty HashMap and ArrayList
Reviewed-by: mduigou, alanb, bchristi, martin
Contributed-by: Sergey Linetskiy <sergey.linetskiy@oracle.com>, John Rose <john.r.rose@oracle.com>, Mike Duigou <mike.duigou@oracle.com>

   1 /*
   2  * Copyright (c) 1997, 2012, 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 import java.io.*;
  28 
  29 /**
  30  * Hash table based implementation of the <tt>Map</tt> interface.  This
  31  * implementation provides all of the optional map operations, and permits
  32  * <tt>null</tt> values and the <tt>null</tt> key.  (The <tt>HashMap</tt>
  33  * class is roughly equivalent to <tt>Hashtable</tt>, except that it is
  34  * unsynchronized and permits nulls.)  This class makes no guarantees as to
  35  * the order of the map; in particular, it does not guarantee that the order
  36  * will remain constant over time.
  37  *
  38  * <p>This implementation provides constant-time performance for the basic
  39  * operations (<tt>get</tt> and <tt>put</tt>), assuming the hash function
  40  * disperses the elements properly among the buckets.  Iteration over
  41  * collection views requires time proportional to the "capacity" of the
  42  * <tt>HashMap</tt> instance (the number of buckets) plus its size (the number
  43  * of key-value mappings).  Thus, it's very important not to set the initial
  44  * capacity too high (or the load factor too low) if iteration performance is
  45  * important.
  46  *
  47  * <p>An instance of <tt>HashMap</tt> has two parameters that affect its
  48  * performance: <i>initial capacity</i> and <i>load factor</i>.  The
  49  * <i>capacity</i> is the number of buckets in the hash table, and the initial
  50  * capacity is simply the capacity at the time the hash table is created.  The
  51  * <i>load factor</i> is a measure of how full the hash table is allowed to
  52  * get before its capacity is automatically increased.  When the number of
  53  * entries in the hash table exceeds the product of the load factor and the
  54  * current capacity, the hash table is <i>rehashed</i> (that is, internal data
  55  * structures are rebuilt) so that the hash table has approximately twice the
  56  * number of buckets.
  57  *
  58  * <p>As a general rule, the default load factor (.75) offers a good tradeoff
  59  * between time and space costs.  Higher values decrease the space overhead
  60  * but increase the lookup cost (reflected in most of the operations of the
  61  * <tt>HashMap</tt> class, including <tt>get</tt> and <tt>put</tt>).  The
  62  * expected number of entries in the map and its load factor should be taken
  63  * into account when setting its initial capacity, so as to minimize the
  64  * number of rehash operations.  If the initial capacity is greater
  65  * than the maximum number of entries divided by the load factor, no
  66  * rehash operations will ever occur.
  67  *
  68  * <p>If many mappings are to be stored in a <tt>HashMap</tt> instance,
  69  * creating it with a sufficiently large capacity will allow the mappings to
  70  * be stored more efficiently than letting it perform automatic rehashing as
  71  * needed to grow the table.
  72  *
  73  * <p><strong>Note that this implementation is not synchronized.</strong>
  74  * If multiple threads access a hash map concurrently, and at least one of
  75  * the threads modifies the map structurally, it <i>must</i> be
  76  * synchronized externally.  (A structural modification is any operation
  77  * that adds or deletes one or more mappings; merely changing the value
  78  * associated with a key that an instance already contains is not a
  79  * structural modification.)  This is typically accomplished by
  80  * synchronizing on some object that naturally encapsulates the map.
  81  *
  82  * If no such object exists, the map should be "wrapped" using the
  83  * {@link Collections#synchronizedMap Collections.synchronizedMap}
  84  * method.  This is best done at creation time, to prevent accidental
  85  * unsynchronized access to the map:<pre>
  86  *   Map m = Collections.synchronizedMap(new HashMap(...));</pre>
  87  *
  88  * <p>The iterators returned by all of this class's "collection view methods"
  89  * are <i>fail-fast</i>: if the map is structurally modified at any time after
  90  * the iterator is created, in any way except through the iterator's own
  91  * <tt>remove</tt> method, the iterator will throw a
  92  * {@link ConcurrentModificationException}.  Thus, in the face of concurrent
  93  * modification, the iterator fails quickly and cleanly, rather than risking
  94  * arbitrary, non-deterministic behavior at an undetermined time in the
  95  * future.
  96  *
  97  * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
  98  * as it is, generally speaking, impossible to make any hard guarantees in the
  99  * presence of unsynchronized concurrent modification.  Fail-fast iterators
 100  * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
 101  * Therefore, it would be wrong to write a program that depended on this
 102  * exception for its correctness: <i>the fail-fast behavior of iterators
 103  * should be used only to detect bugs.</i>
 104  *
 105  * <p>This class is a member of the
 106  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 107  * Java Collections Framework</a>.
 108  *
 109  * @param <K> the type of keys maintained by this map
 110  * @param <V> the type of mapped values
 111  *
 112  * @author  Doug Lea
 113  * @author  Josh Bloch
 114  * @author  Arthur van Hoff
 115  * @author  Neal Gafter
 116  * @see     Object#hashCode()
 117  * @see     Collection
 118  * @see     Map
 119  * @see     TreeMap
 120  * @see     Hashtable
 121  * @since   1.2
 122  */
 123 
 124 public class HashMap<K,V>
 125     extends AbstractMap<K,V>
 126     implements Map<K,V>, Cloneable, Serializable
 127 {
 128 
 129     /**
 130      * The default initial capacity - MUST be a power of two.
 131      */
 132     static final int DEFAULT_INITIAL_CAPACITY = 16;
 133 
 134     /**
 135      * The maximum capacity, used if a higher value is implicitly specified
 136      * by either of the constructors with arguments.
 137      * MUST be a power of two <= 1<<30.
 138      */
 139     static final int MAXIMUM_CAPACITY = 1 << 30;
 140 
 141     /**
 142      * The load factor used when none specified in constructor.
 143      */
 144     static final float DEFAULT_LOAD_FACTOR = 0.75f;
 145 
 146     /**





 147      * The table, resized as necessary. Length MUST Always be a power of two.
 148      */
 149     transient Entry<?,?>[] table;
 150 
 151     /**
 152      * The number of key-value mappings contained in this map.
 153      */
 154     transient int size;
 155 
 156     /**
 157      * The next size value at which to resize (capacity * load factor).


 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         if (k instanceof String) {
 292             return ((String) k).hash32();
 293         }
 294 
 295         int  h = hashSeed ^ k.hashCode();
 296 
 297         // This function ensures that hashCodes that differ only by
 298         // constant multiples at each bit position have a bounded
 299         // number of collisions (approximately 8 at default load factor).
 300         h ^= (h >>> 20) ^ (h >>> 12);
 301         return h ^ (h >>> 7) ^ (h >>> 4);
 302     }
 303 
 304     /**
 305      * Returns index for hash code h.
 306      */
 307     static int indexFor(int h, int length) {

 308         return h & (length-1);
 309     }
 310 
 311     /**
 312      * Returns the number of key-value mappings in this map.
 313      *
 314      * @return the number of key-value mappings in this map
 315      */
 316     public int size() {
 317         return size;
 318     }
 319 
 320     /**
 321      * Returns <tt>true</tt> if this map contains no key-value mappings.
 322      *
 323      * @return <tt>true</tt> if this map contains no key-value mappings
 324      */
 325     public boolean isEmpty() {
 326         return size == 0;
 327     }
 328 
 329     /**
 330      * Returns the value to which the specified key is mapped,
 331      * or {@code null} if this map contains no mapping for the key.
 332      *
 333      * <p>More formally, if this map contains a mapping from a key
 334      * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
 335      * key.equals(k))}, then this method returns {@code v}; otherwise
 336      * it returns {@code null}.  (There can be at most one such mapping.)
 337      *
 338      * <p>A return value of {@code null} does not <i>necessarily</i>
 339      * indicate that the map contains no mapping for the key; it's also
 340      * possible that the map explicitly maps the key to {@code null}.
 341      * The {@link #containsKey containsKey} operation may be used to
 342      * distinguish these two cases.
 343      *
 344      * @see #put(Object, Object)
 345      */
 346     @SuppressWarnings("unchecked")
 347     public V get(Object key) {
 348         Entry<K,V> entry = getEntry(key);
 349 
 350         return null == entry ? null : entry.getValue();
 351     }
 352 
 353     /**
 354      * Returns <tt>true</tt> if this map contains a mapping for the
 355      * specified key.
 356      *
 357      * @param   key   The key whose presence in this map is to be tested
 358      * @return <tt>true</tt> if this map contains a mapping for the specified
 359      * key.
 360      */
 361     public boolean containsKey(Object key) {
 362         return getEntry(key) != null;
 363     }
 364 
 365     /**
 366      * Returns the entry associated with the specified key in the
 367      * HashMap.  Returns null if the HashMap contains no mapping
 368      * for the key.
 369      */
 370     @SuppressWarnings("unchecked")
 371     final Entry<K,V> getEntry(Object key) {




 372         int hash = (key == null) ? 0 : hash(key);
 373         for (Entry<?,?> e = table[indexFor(hash, table.length)];
 374              e != null;
 375              e = e.next) {
 376             Object k;
 377             if (e.hash == hash &&
 378                 ((k = e.key) == key || (key != null && key.equals(k))))
 379                 return (Entry<K,V>)e;
 380         }
 381         return null;
 382     }
 383 
 384 
 385     /**
 386      * Associates the specified value with the specified key in this map.
 387      * If the map previously contained a mapping for the key, the old
 388      * value is replaced.
 389      *
 390      * @param key key with which the specified value is to be associated
 391      * @param value value to be associated with the specified key
 392      * @return the previous value associated with <tt>key</tt>, or
 393      *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
 394      *         (A <tt>null</tt> return can also indicate that the map
 395      *         previously associated <tt>null</tt> with <tt>key</tt>.)
 396      */
 397     public V put(K key, V value) {



 398         if (key == null)
 399             return putForNullKey(value);
 400         int hash = hash(key);
 401         int i = indexFor(hash, table.length);
 402         @SuppressWarnings("unchecked")
 403         Entry<K,V> e = (Entry<K,V>)table[i];
 404         for(; e != null; e = e.next) {
 405             Object k;
 406             if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
 407                 V oldValue = e.value;
 408                 e.value = value;
 409                 e.recordAccess(this);
 410                 return oldValue;
 411             }
 412         }
 413 
 414         modCount++;
 415         addEntry(hash, key, value, i);
 416         return null;
 417     }
 418 
 419     /**
 420      * Offloaded version of put for null keys
 421      */
 422     private V putForNullKey(V value) {
 423         @SuppressWarnings("unchecked")
 424         Entry<K,V> e = (Entry<K,V>)table[0];
 425         for(; e != null; e = e.next) {
 426             if (e.key == null) {
 427                 V oldValue = e.value;
 428                 e.value = value;
 429                 e.recordAccess(this);
 430                 return oldValue;
 431             }
 432         }
 433         modCount++;
 434         addEntry(0, null, value, 0);
 435         return null;
 436     }
 437 
 438     /**
 439      * This method is used instead of put by constructors and
 440      * pseudoconstructors (clone, readObject).  It does not resize the table,
 441      * check for comodification, etc.  It calls createEntry rather than
 442      * addEntry.
 443      */
 444     private void putForCreate(K key, V value) {
 445         int hash = null == key ? 0 : hash(key);
 446         int i = indexFor(hash, table.length);
 447 
 448         /**
 449          * Look for preexisting entry for key.  This will never happen for
 450          * clone or deserialize.  It will only happen for construction if the
 451          * input Map is a sorted map whose ordering is inconsistent w/ equals.
 452          */
 453         for (@SuppressWarnings("unchecked")
 454              Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) {
 455             Object k;
 456             if (e.hash == hash &&
 457                 ((k = e.key) == key || (key != null && key.equals(k)))) {
 458                 e.value = value;
 459                 return;
 460             }
 461         }
 462 
 463         createEntry(hash, key, value, i);
 464     }
 465 
 466     private void putAllForCreate(Map<? extends K, ? extends V> m) {
 467         for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
 468             putForCreate(e.getKey(), e.getValue());
 469     }
 470 
 471     /**
 472      * Rehashes the contents of this map into a new array with a
 473      * larger capacity.  This method is called automatically when the
 474      * number of keys in this map reaches its threshold.
 475      *
 476      * If current capacity is MAXIMUM_CAPACITY, this method does not
 477      * resize the map, but sets threshold to Integer.MAX_VALUE.
 478      * This has the effect of preventing future calls.
 479      *
 480      * @param newCapacity the new capacity, MUST be a power of two;
 481      *        must be greater than current capacity unless current
 482      *        capacity is MAXIMUM_CAPACITY (in which case value
 483      *        is irrelevant).
 484      */
 485     void resize(int newCapacity) {
 486         Entry<?,?>[] oldTable = table;
 487         int oldCapacity = oldTable.length;
 488         if (oldCapacity == MAXIMUM_CAPACITY) {
 489             threshold = Integer.MAX_VALUE;
 490             return;
 491         }
 492 
 493         Entry<?,?>[] newTable = new Entry<?,?>[newCapacity];
 494         transfer(newTable);
 495         table = newTable;
 496         threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
 497     }
 498 
 499     /**
 500      * Transfers all entries from current table to newTable.
 501      */
 502     @SuppressWarnings("unchecked")
 503     void transfer(Entry<?,?>[] newTable) {
 504         Entry<?,?>[] src = table;
 505         int newCapacity = newTable.length;
 506         for (int j = 0; j < src.length; j++ ) {
 507             Entry<K,V> e = (Entry<K,V>) src[j];
 508             while(null != e) {
 509                 Entry<K,V> next = e.next;
 510                 int i = indexFor(e.hash, newCapacity);
 511                 e.next = (Entry<K,V>) newTable[i];
 512                 newTable[i] = e;
 513                 e = next;
 514             }
 515         }
 516         Arrays.fill(table, null);
 517     }
 518 
 519     /**
 520      * Copies all of the mappings from the specified map to this map.
 521      * These mappings will replace any mappings that this map had for
 522      * any of the keys currently in the specified map.
 523      *
 524      * @param m mappings to be stored in this map
 525      * @throws NullPointerException if the specified map is null
 526      */
 527     public void putAll(Map<? extends K, ? extends V> m) {
 528         int numKeysToBeAdded = m.size();
 529         if (numKeysToBeAdded == 0)
 530             return;
 531 




 532         /*
 533          * Expand the map if the map if the number of mappings to be added
 534          * is greater than or equal to threshold.  This is conservative; the
 535          * obvious condition is (m.size() + size) >= threshold, but this
 536          * condition could result in a map with twice the appropriate capacity,
 537          * if the keys to be added overlap with the keys already in this map.
 538          * By using the conservative calculation, we subject ourself
 539          * to at most one extra resize.
 540          */
 541         if (numKeysToBeAdded > threshold) {
 542             int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
 543             if (targetCapacity > MAXIMUM_CAPACITY)
 544                 targetCapacity = MAXIMUM_CAPACITY;
 545             int newCapacity = table.length;
 546             while (newCapacity < targetCapacity)
 547                 newCapacity <<= 1;
 548             if (newCapacity > table.length)
 549                 resize(newCapacity);
 550         }
 551 
 552         for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
 553             put(e.getKey(), e.getValue());
 554     }
 555 
 556     /**
 557      * Removes the mapping for the specified key from this map if present.
 558      *
 559      * @param  key key whose mapping is to be removed from the map
 560      * @return the previous value associated with <tt>key</tt>, or
 561      *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
 562      *         (A <tt>null</tt> return can also indicate that the map
 563      *         previously associated <tt>null</tt> with <tt>key</tt>.)
 564      */
 565     public V remove(Object key) {
 566         Entry<K,V> e = removeEntryForKey(key);
 567         return (e == null ? null : e.value);
 568     }
 569 
 570     /**
 571      * Removes and returns the entry associated with the specified key
 572      * in the HashMap.  Returns null if the HashMap contains no mapping
 573      * for this key.
 574      */
 575     final Entry<K,V> removeEntryForKey(Object key) {



 576         int hash = (key == null) ? 0 : hash(key);
 577         int i = indexFor(hash, table.length);
 578         @SuppressWarnings("unchecked")
 579             Entry<K,V> prev = (Entry<K,V>)table[i];
 580         Entry<K,V> e = prev;
 581 
 582         while (e != null) {
 583             Entry<K,V> next = e.next;
 584             Object k;
 585             if (e.hash == hash &&
 586                 ((k = e.key) == key || (key != null && key.equals(k)))) {
 587                 modCount++;
 588                 size--;
 589                 if (prev == e)
 590                     table[i] = next;
 591                 else
 592                     prev.next = next;
 593                 e.recordRemoval(this);
 594                 return e;
 595             }
 596             prev = e;
 597             e = next;
 598         }
 599 
 600         return e;
 601     }
 602 
 603     /**
 604      * Special version of remove for EntrySet using {@code Map.Entry.equals()}
 605      * for matching.
 606      */
 607     final Entry<K,V> removeMapping(Object o) {
 608         if (!(o instanceof Map.Entry))
 609             return null;
 610 
 611         Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
 612         Object key = entry.getKey();
 613         int hash = (key == null) ? 0 : hash(key);
 614         int i = indexFor(hash, table.length);
 615         @SuppressWarnings("unchecked")
 616             Entry<K,V> prev = (Entry<K,V>)table[i];
 617         Entry<K,V> e = prev;
 618 
 619         while (e != null) {
 620             Entry<K,V> next = e.next;
 621             if (e.hash == hash && e.equals(entry)) {
 622                 modCount++;
 623                 size--;
 624                 if (prev == e)
 625                     table[i] = next;
 626                 else
 627                     prev.next = next;
 628                 e.recordRemoval(this);
 629                 return e;
 630             }
 631             prev = e;
 632             e = next;
 633         }
 634 
 635         return e;
 636     }
 637 
 638     /**
 639      * Removes all of the mappings from this map.
 640      * The map will be empty after this call returns.
 641      */
 642     public void clear() {
 643         modCount++;
 644         Entry<?,?>[] tab = table;
 645         for (int i = 0; i < tab.length; i++)
 646             tab[i] = null;
 647         size = 0;
 648     }
 649 
 650     /**
 651      * Returns <tt>true</tt> if this map maps one or more keys to the
 652      * specified value.
 653      *
 654      * @param value value whose presence in this map is to be tested
 655      * @return <tt>true</tt> if this map maps one or more keys to the
 656      *         specified value
 657      */
 658     public boolean containsValue(Object value) {




 659         if (value == null)
 660             return containsNullValue();
 661 
 662         Entry<?,?>[] tab = table;
 663         for (int i = 0; i < tab.length ; i++)
 664             for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
 665                 if (value.equals(e.value))
 666                     return true;
 667         return false;
 668     }
 669 
 670     /**
 671      * Special-case code for containsValue with null argument
 672      */
 673     private boolean containsNullValue() {
 674         Entry<?,?>[] tab = table;
 675         for (int i = 0; i < tab.length ; i++)
 676             for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
 677                 if (e.value == null)
 678                     return true;
 679         return false;
 680     }
 681 
 682     /**
 683      * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
 684      * values themselves are not cloned.
 685      *
 686      * @return a shallow copy of this map
 687      */
 688     @SuppressWarnings("unchecked")
 689     public Object clone() {
 690         HashMap<K,V> result = null;
 691         try {
 692             result = (HashMap<K,V>)super.clone();
 693         } catch (CloneNotSupportedException e) {
 694             // assert false;
 695         }
 696         result.table = new Entry<?,?>[table.length];


 697         result.entrySet = null;
 698         result.modCount = 0;
 699         result.size = 0;
 700         result.init();
 701         result.putAllForCreate(this);
 702 
 703         return result;
 704     }
 705 
 706     static class Entry<K,V> implements Map.Entry<K,V> {
 707         final K key;
 708         V value;
 709         Entry<K,V> next;
 710         final int hash;
 711 
 712         /**
 713          * Creates new entry.
 714          */
 715         Entry(int h, K k, V v, Entry<K,V> n) {
 716             value = v;
 717             next = n;
 718             key = k;
 719             hash = h;
 720         }
 721 
 722         public final K getKey() {
 723             return key;
 724         }
 725 
 726         public final V getValue() {
 727             return value;
 728         }
 729 
 730         public final V setValue(V newValue) {
 731             V oldValue = value;
 732             value = newValue;
 733             return oldValue;
 734         }
 735 
 736         public final boolean equals(Object o) {
 737             if (!(o instanceof Map.Entry))
 738                 return false;
 739             Map.Entry<?,?> e = (Map.Entry<?,?>)o;
 740             Object k1 = getKey();
 741             Object k2 = e.getKey();
 742             if (k1 == k2 || (k1 != null && k1.equals(k2))) {
 743                 Object v1 = getValue();
 744                 Object v2 = e.getValue();
 745                 if (v1 == v2 || (v1 != null && v1.equals(v2)))
 746                     return true;
 747             }
 748             return false;
 749         }
 750 
 751         public final int hashCode() {
 752             return (key==null   ? 0 : key.hashCode()) ^
 753                    (value==null ? 0 : value.hashCode());
 754         }
 755 
 756         public final String toString() {
 757             return getKey() + "=" + getValue();
 758         }
 759 
 760         /**
 761          * This method is invoked whenever the value in an entry is
 762          * overwritten by an invocation of put(k,v) for a key k that's already
 763          * in the HashMap.
 764          */
 765         void recordAccess(HashMap<K,V> m) {
 766         }
 767 
 768         /**
 769          * This method is invoked whenever the entry is
 770          * removed from the table.
 771          */
 772         void recordRemoval(HashMap<K,V> m) {
 773         }
 774     }
 775 
 776     /**
 777      * Adds a new entry with the specified key, value and hash code to
 778      * the specified bucket.  It is the responsibility of this
 779      * method to resize the table if appropriate.
 780      *
 781      * Subclass overrides this to alter the behavior of put method.
 782      */
 783     void addEntry(int hash, K key, V value, int bucketIndex) {
 784         if ((size >= threshold) && (null != table[bucketIndex])) {
 785             resize(2 * table.length);
 786             hash = (null != key) ? hash(key) : 0;
 787             bucketIndex = indexFor(hash, table.length);
 788         }
 789 
 790         createEntry(hash, key, value, bucketIndex);
 791     }
 792 
 793     /**
 794      * Like addEntry except that this version is used when creating entries
 795      * as part of Map construction or "pseudo-construction" (cloning,
 796      * deserialization).  This version needn't worry about resizing the table.
 797      *
 798      * Subclass overrides this to alter the behavior of HashMap(Map),
 799      * clone, and readObject.
 800      */
 801     void createEntry(int hash, K key, V value, int bucketIndex) {
 802         @SuppressWarnings("unchecked")
 803             Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
 804         table[bucketIndex] = new Entry<>(hash, key, value, e);
 805         size++;
 806     }
 807 
 808     private abstract class HashIterator<E> implements Iterator<E> {
 809         Entry<?,?> next;        // next entry to return
 810         int expectedModCount;   // For fast-fail
 811         int index;              // current slot
 812         Entry<?,?> current;     // current entry
 813 
 814         HashIterator() {
 815             expectedModCount = modCount;
 816             if (size > 0) { // advance to first entry
 817                 Entry<?,?>[] t = table;
 818                 while (index < t.length && (next = t[index++]) == null)
 819                     ;
 820             }
 821         }
 822 
 823         public final boolean hasNext() {
 824             return next != null;
 825         }
 826 
 827         @SuppressWarnings("unchecked")
 828         final Entry<K,V> nextEntry() {
 829             if (modCount != expectedModCount)
 830                 throw new ConcurrentModificationException();
 831             Entry<?,?> e = next;
 832             if (e == null)
 833                 throw new NoSuchElementException();
 834 
 835             if ((next = e.next) == null) {
 836                 Entry<?,?>[] t = table;
 837                 while (index < t.length && (next = t[index++]) == null)
 838                     ;
 839             }
 840             current = e;
 841             return (Entry<K,V>)e;
 842         }
 843 
 844         public void remove() {
 845             if (current == null)
 846                 throw new IllegalStateException();
 847             if (modCount != expectedModCount)
 848                 throw new ConcurrentModificationException();
 849             Object k = current.key;
 850             current = null;
 851             HashMap.this.removeEntryForKey(k);
 852             expectedModCount = modCount;
 853         }
 854     }
 855 
 856     private final class ValueIterator extends HashIterator<V> {
 857         public V next() {
 858             return nextEntry().value;
 859         }
 860     }
 861 
 862     private final class KeyIterator extends HashIterator<K> {
 863         public K next() {
 864             return nextEntry().getKey();
 865         }
 866     }
 867 
 868     private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
 869         public Map.Entry<K,V> next() {
 870             return nextEntry();
 871         }
 872     }
 873 
 874     // Subclass overrides these to alter behavior of views' iterator() method
 875     Iterator<K> newKeyIterator()   {
 876         return new KeyIterator();
 877     }
 878     Iterator<V> newValueIterator()   {
 879         return new ValueIterator();
 880     }
 881     Iterator<Map.Entry<K,V>> newEntryIterator()   {
 882         return new EntryIterator();
 883     }
 884 
 885 
 886     // Views
 887 
 888     private transient Set<Map.Entry<K,V>> entrySet = null;
 889 
 890     /**
 891      * Returns a {@link Set} view of the keys contained in this map.
 892      * The set is backed by the map, so changes to the map are
 893      * reflected in the set, and vice-versa.  If the map is modified
 894      * while an iteration over the set is in progress (except through
 895      * the iterator's own <tt>remove</tt> operation), the results of
 896      * the iteration are undefined.  The set supports element removal,
 897      * which removes the corresponding mapping from the map, via the
 898      * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
 899      * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
 900      * operations.  It does not support the <tt>add</tt> or <tt>addAll</tt>
 901      * operations.
 902      */
 903     public Set<K> keySet() {
 904         Set<K> ks = keySet;
 905         return (ks != null ? ks : (keySet = new KeySet()));
 906     }
 907 
 908     private final class KeySet extends AbstractSet<K> {
 909         public Iterator<K> iterator() {
 910             return newKeyIterator();
 911         }
 912         public int size() {
 913             return size;
 914         }
 915         public boolean contains(Object o) {
 916             return containsKey(o);
 917         }
 918         public boolean remove(Object o) {
 919             return HashMap.this.removeEntryForKey(o) != null;
 920         }
 921         public void clear() {
 922             HashMap.this.clear();
 923         }
 924     }
 925 
 926     /**
 927      * Returns a {@link Collection} view of the values contained in this map.
 928      * The collection is backed by the map, so changes to the map are
 929      * reflected in the collection, and vice-versa.  If the map is
 930      * modified while an iteration over the collection is in progress
 931      * (except through the iterator's own <tt>remove</tt> operation),
 932      * the results of the iteration are undefined.  The collection
 933      * supports element removal, which removes the corresponding
 934      * mapping from the map, via the <tt>Iterator.remove</tt>,
 935      * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
 936      * <tt>retainAll</tt> and <tt>clear</tt> operations.  It does not
 937      * support the <tt>add</tt> or <tt>addAll</tt> operations.
 938      */
 939     public Collection<V> values() {
 940         Collection<V> vs = values;
 941         return (vs != null ? vs : (values = new Values()));
 942     }
 943 
 944     private final class Values extends AbstractCollection<V> {
 945         public Iterator<V> iterator() {
 946             return newValueIterator();
 947         }
 948         public int size() {
 949             return size;
 950         }
 951         public boolean contains(Object o) {
 952             return containsValue(o);
 953         }
 954         public void clear() {
 955             HashMap.this.clear();
 956         }
 957     }
 958 
 959     /**
 960      * Returns a {@link Set} view of the mappings contained in this map.
 961      * The set is backed by the map, so changes to the map are
 962      * reflected in the set, and vice-versa.  If the map is modified
 963      * while an iteration over the set is in progress (except through
 964      * the iterator's own <tt>remove</tt> operation, or through the
 965      * <tt>setValue</tt> operation on a map entry returned by the
 966      * iterator) the results of the iteration are undefined.  The set
 967      * supports element removal, which removes the corresponding
 968      * mapping from the map, via the <tt>Iterator.remove</tt>,
 969      * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
 970      * <tt>clear</tt> operations.  It does not support the
 971      * <tt>add</tt> or <tt>addAll</tt> operations.
 972      *
 973      * @return a set view of the mappings contained in this map
 974      */
 975     public Set<Map.Entry<K,V>> entrySet() {
 976         return entrySet0();
 977     }
 978 
 979     private Set<Map.Entry<K,V>> entrySet0() {
 980         Set<Map.Entry<K,V>> es = entrySet;
 981         return es != null ? es : (entrySet = new EntrySet());
 982     }
 983 
 984     private final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
 985         public Iterator<Map.Entry<K,V>> iterator() {
 986             return newEntryIterator();
 987         }
 988         public boolean contains(Object o) {
 989             if (!(o instanceof Map.Entry))
 990                 return false;
 991             Map.Entry<?,?> e = (Map.Entry<?,?>) o;
 992             Entry<K,V> candidate = getEntry(e.getKey());
 993             return candidate != null && candidate.equals(e);
 994         }
 995         public boolean remove(Object o) {
 996             return removeMapping(o) != null;
 997         }
 998         public int size() {
 999             return size;
1000         }
1001         public void clear() {
1002             HashMap.this.clear();
1003         }
1004     }
1005 
1006     /**
1007      * Save the state of the <tt>HashMap</tt> instance to a stream (i.e.,
1008      * serialize it).
1009      *
1010      * @serialData The <i>capacity</i> of the HashMap (the length of the
1011      *             bucket array) is emitted (int), followed by the
1012      *             <i>size</i> (an int, the number of key-value
1013      *             mappings), followed by the key (Object) and value (Object)
1014      *             for each key-value mapping.  The key-value mappings are
1015      *             emitted in no particular order.
1016      */
1017     private void writeObject(java.io.ObjectOutputStream s)
1018         throws IOException
1019     {
1020         Iterator<Map.Entry<K,V>> i =
1021             (size > 0) ? entrySet0().iterator() : null;
1022 
1023         // Write out the threshold, loadfactor, and any hidden stuff
1024         s.defaultWriteObject();
1025 
1026         // Write out number of buckets



1027         s.writeInt(table.length);

1028 
1029         // Write out size (number of Mappings)
1030         s.writeInt(size);
1031 
1032         // Write out keys and values (alternating)
1033         if (size > 0) {
1034             for(Map.Entry<K,V> e : entrySet0()) {
1035                 s.writeObject(e.getKey());
1036                 s.writeObject(e.getValue());
1037             }
1038         }
1039     }
1040 
1041     private static final long serialVersionUID = 362498820763181265L;
1042 
1043     /**
1044      * Reconstitute the {@code HashMap} instance from a stream (i.e.,
1045      * deserialize it).
1046      */
1047     private void readObject(java.io.ObjectInputStream s)
1048          throws IOException, ClassNotFoundException
1049     {
1050         // Read in the threshold (ignored), loadfactor, and any hidden stuff
1051         s.defaultReadObject();
1052         if (loadFactor <= 0 || Float.isNaN(loadFactor))
1053             throw new InvalidObjectException("Illegal load factor: " +
1054                                                loadFactor);

1055 
1056         // set hashMask
1057         Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET,
1058                 sun.misc.Hashing.randomHashSeed(this));








1059 
1060         // Read in number of buckets and allocate the bucket array;
1061         s.readInt(); // ignored
1062 
1063         // Read number of mappings
1064         int mappings = s.readInt();
1065         if (mappings < 0)
1066             throw new InvalidObjectException("Illegal mappings count: " +
1067                                                mappings);
1068 
1069         int initialCapacity = (int) Math.min(
1070                 // capacity chosen by number of mappings
1071                 // and desired load (if >= 0.25)
1072                 mappings * Math.min(1 / loadFactor, 4.0f),
1073                 // we have limits...
1074                 HashMap.MAXIMUM_CAPACITY);
1075         int capacity = 1;
1076         // find smallest power of two which holds all mappings
1077         while (capacity < initialCapacity) {
1078             capacity <<= 1;





1079         }
1080 
1081         table = new Entry<?,?>[capacity];
1082         threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
1083         init();  // Give subclass a chance to do its thing.
1084 
1085 
1086         // Read the keys and values, and put the mappings in the HashMap
1087         for (int i=0; i<mappings; i++) {
1088             @SuppressWarnings("unchecked")
1089                 K key = (K) s.readObject();
1090             @SuppressWarnings("unchecked")
1091                 V value = (V) s.readObject();
1092             putForCreate(key, value);
1093         }
1094     }
1095 
1096     // These methods are used when serializing HashSets
1097     int   capacity()     { return table.length; }
1098     float loadFactor()   { return loadFactor;   }
1099 }
--- EOF ---