rev 13463 : 8148044: Remove Enum[0] constants from EnumSet and EnumMap
Reviewed-by: TBD

   1 /*
   2  * Copyright (c) 2003, 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 

  28 import jdk.internal.misc.SharedSecrets;
  29 
  30 /**
  31  * A specialized {@link Map} implementation for use with enum type keys.  All
  32  * of the keys in an enum map must come from a single enum type that is
  33  * specified, explicitly or implicitly, when the map is created.  Enum maps
  34  * are represented internally as arrays.  This representation is extremely
  35  * compact and efficient.
  36  *
  37  * <p>Enum maps are maintained in the <i>natural order</i> of their keys
  38  * (the order in which the enum constants are declared).  This is reflected
  39  * in the iterators returned by the collections views ({@link #keySet()},
  40  * {@link #entrySet()}, and {@link #values()}).
  41  *
  42  * <p>Iterators returned by the collection views are <i>weakly consistent</i>:
  43  * they will never throw {@link ConcurrentModificationException} and they may
  44  * or may not show the effects of any modifications to the map that occur while
  45  * the iteration is in progress.
  46  *
  47  * <p>Null keys are not permitted.  Attempts to insert a null key will
  48  * throw {@link NullPointerException}.  Attempts to test for the
  49  * presence of a null key or to remove one will, however, function properly.
  50  * Null values are permitted.
  51 
  52  * <P>Like most collection implementations {@code EnumMap} is not
  53  * synchronized. If multiple threads access an enum map concurrently, and at
  54  * least one of the threads modifies the map, it should be synchronized
  55  * externally.  This is typically accomplished by synchronizing on some
  56  * object that naturally encapsulates the enum map.  If no such object exists,
  57  * the map should be "wrapped" using the {@link Collections#synchronizedMap}
  58  * method.  This is best done at creation time, to prevent accidental
  59  * unsynchronized access:
  60  *
  61  * <pre>
  62  *     Map&lt;EnumKey, V&gt; m
  63  *         = Collections.synchronizedMap(new EnumMap&lt;EnumKey, V&gt;(...));
  64  * </pre>
  65  *
  66  * <p>Implementation note: All basic operations execute in constant time.
  67  * They are likely (though not guaranteed) to be faster than their
  68  * {@link HashMap} counterparts.
  69  *
  70  * <p>This class is a member of the
  71  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
  72  * Java Collections Framework</a>.
  73  *
  74  * @author Josh Bloch
  75  * @see EnumSet
  76  * @since 1.5
  77  */
  78 public class EnumMap<K extends Enum<K>, V> extends AbstractMap<K, V>
  79     implements java.io.Serializable, Cloneable
  80 {
  81     /**
  82      * The {@code Class} object for the enum type of all the keys of this map.
  83      *
  84      * @serial
  85      */
  86     private final Class<K> keyType;
  87 
  88     /**
  89      * All of the values comprising K.  (Cached for performance.)
  90      */
  91     private transient K[] keyUniverse;
  92 
  93     /**
  94      * Array representation of this map.  The ith element is the value
  95      * to which universe[i] is currently mapped, or null if it isn't
  96      * mapped to anything, or NULL if it's mapped to null.
  97      */
  98     private transient Object[] vals;
  99 
 100     /**
 101      * The number of mappings in this map.
 102      */
 103     private transient int size = 0;
 104 
 105     /**
 106      * Distinguished non-null value for representing null values.
 107      */
 108     private static final Object NULL = new Object() {
 109         public int hashCode() {
 110             return 0;
 111         }
 112 
 113         public String toString() {
 114             return "java.util.EnumMap.NULL";
 115         }
 116     };
 117 
 118     private Object maskNull(Object value) {
 119         return (value == null ? NULL : value);
 120     }
 121 
 122     @SuppressWarnings("unchecked")
 123     private V unmaskNull(Object value) {
 124         return (V)(value == NULL ? null : value);
 125     }


 126 
 127     /**
 128      * Creates an empty enum map with the specified key type.
 129      *
 130      * @param keyType the class object of the key type for this enum map
 131      * @throws NullPointerException if {@code keyType} is null
 132      */
 133     public EnumMap(Class<K> keyType) {
 134         this.keyType = keyType;
 135         keyUniverse = getKeyUniverse(keyType);
 136         vals = new Object[keyUniverse.length];
 137     }
 138 
 139     /**
 140      * Creates an enum map with the same key type as the specified enum
 141      * map, initially containing the same mappings (if any).
 142      *
 143      * @param m the enum map from which to initialize this enum map
 144      * @throws NullPointerException if {@code m} is null
 145      */
 146     public EnumMap(EnumMap<K, ? extends V> m) {
 147         keyType = m.keyType;
 148         keyUniverse = m.keyUniverse;
 149         vals = m.vals.clone();
 150         size = m.size;
 151     }
 152 
 153     /**
 154      * Creates an enum map initialized from the specified map.  If the
 155      * specified map is an {@code EnumMap} instance, this constructor behaves
 156      * identically to {@link #EnumMap(EnumMap)}.  Otherwise, the specified map
 157      * must contain at least one mapping (in order to determine the new
 158      * enum map's key type).
 159      *
 160      * @param m the map from which to initialize this enum map
 161      * @throws IllegalArgumentException if {@code m} is not an
 162      *     {@code EnumMap} instance and contains no mappings
 163      * @throws NullPointerException if {@code m} is null
 164      */
 165     public EnumMap(Map<K, ? extends V> m) {
 166         if (m instanceof EnumMap) {
 167             EnumMap<K, ? extends V> em = (EnumMap<K, ? extends V>) m;
 168             keyType = em.keyType;
 169             keyUniverse = em.keyUniverse;
 170             vals = em.vals.clone();
 171             size = em.size;
 172         } else {
 173             if (m.isEmpty())
 174                 throw new IllegalArgumentException("Specified map is empty");
 175             keyType = m.keySet().iterator().next().getDeclaringClass();
 176             keyUniverse = getKeyUniverse(keyType);
 177             vals = new Object[keyUniverse.length];
 178             putAll(m);
 179         }
 180     }
 181 
 182     // Query Operations
 183 
 184     /**
 185      * Returns the number of key-value mappings in this map.
 186      *
 187      * @return the number of key-value mappings in this map
 188      */
 189     public int size() {
 190         return size;
 191     }
 192 
 193     /**
 194      * Returns {@code true} if this map maps one or more keys to the
 195      * specified value.
 196      *
 197      * @param value the value whose presence in this map is to be tested
 198      * @return {@code true} if this map maps one or more keys to this value
 199      */
 200     public boolean containsValue(Object value) {
 201         value = maskNull(value);
 202 
 203         for (Object val : vals)
 204             if (value.equals(val))
 205                 return true;
 206 
 207         return false;
 208     }
 209 
 210     /**
 211      * Returns {@code true} if this map contains a mapping for the specified
 212      * key.
 213      *
 214      * @param key the key whose presence in this map is to be tested
 215      * @return {@code true} if this map contains a mapping for the specified
 216      *            key
 217      */
 218     public boolean containsKey(Object key) {
 219         return isValidKey(key) && vals[((Enum<?>)key).ordinal()] != null;
 220     }
 221 
 222     private boolean containsMapping(Object key, Object value) {
 223         return isValidKey(key) &&
 224             maskNull(value).equals(vals[((Enum<?>)key).ordinal()]);
 225     }
 226 
 227     /**
 228      * Returns the value to which the specified key is mapped,
 229      * or {@code null} if this map contains no mapping for the key.
 230      *
 231      * <p>More formally, if this map contains a mapping from a key
 232      * {@code k} to a value {@code v} such that {@code (key == k)},
 233      * then this method returns {@code v}; otherwise it returns
 234      * {@code null}.  (There can be at most one such mapping.)
 235      *
 236      * <p>A return value of {@code null} does not <i>necessarily</i>
 237      * indicate that the map contains no mapping for the key; it's also
 238      * possible that the map explicitly maps the key to {@code null}.
 239      * The {@link #containsKey containsKey} operation may be used to
 240      * distinguish these two cases.
 241      */
 242     public V get(Object key) {
 243         return (isValidKey(key) ?
 244                 unmaskNull(vals[((Enum<?>)key).ordinal()]) : null);
 245     }
 246 
 247     // Modification Operations
 248 
 249     /**
 250      * Associates the specified value with the specified key in this map.
 251      * If the map previously contained a mapping for this key, the old
 252      * value is replaced.
 253      *
 254      * @param key the key with which the specified value is to be associated
 255      * @param value the value to be associated with the specified key
 256      *
 257      * @return the previous value associated with specified key, or
 258      *     {@code null} if there was no mapping for key.  (A {@code null}
 259      *     return can also indicate that the map previously associated
 260      *     {@code null} with the specified key.)
 261      * @throws NullPointerException if the specified key is null
 262      */
 263     public V put(K key, V value) {
 264         typeCheck(key);
 265 
 266         int index = key.ordinal();
 267         Object oldValue = vals[index];
 268         vals[index] = maskNull(value);
 269         if (oldValue == null)
 270             size++;
 271         return unmaskNull(oldValue);
 272     }
 273 
 274     /**
 275      * Removes the mapping for this key from this map if present.
 276      *
 277      * @param key the key whose mapping is to be removed from the map
 278      * @return the previous value associated with specified key, or
 279      *     {@code null} if there was no entry for key.  (A {@code null}
 280      *     return can also indicate that the map previously associated
 281      *     {@code null} with the specified key.)
 282      */
 283     public V remove(Object key) {
 284         if (!isValidKey(key))
 285             return null;
 286         int index = ((Enum<?>)key).ordinal();
 287         Object oldValue = vals[index];
 288         vals[index] = null;
 289         if (oldValue != null)
 290             size--;
 291         return unmaskNull(oldValue);
 292     }
 293 
 294     private boolean removeMapping(Object key, Object value) {
 295         if (!isValidKey(key))
 296             return false;
 297         int index = ((Enum<?>)key).ordinal();
 298         if (maskNull(value).equals(vals[index])) {
 299             vals[index] = null;
 300             size--;
 301             return true;
 302         }
 303         return false;
 304     }
 305 
 306     /**
 307      * Returns true if key is of the proper type to be a key in this
 308      * enum map.
 309      */
 310     private boolean isValidKey(Object key) {
 311         if (key == null)
 312             return false;
 313 
 314         // Cheaper than instanceof Enum followed by getDeclaringClass
 315         Class<?> keyClass = key.getClass();
 316         return keyClass == keyType || keyClass.getSuperclass() == keyType;
 317     }
 318 
 319     // Bulk Operations
 320 
 321     /**
 322      * Copies all of the mappings from the specified map to this map.
 323      * These mappings will replace any mappings that this map had for
 324      * any of the keys currently in the specified map.
 325      *
 326      * @param m the mappings to be stored in this map
 327      * @throws NullPointerException the specified map is null, or if
 328      *     one or more keys in the specified map are null
 329      */
 330     public void putAll(Map<? extends K, ? extends V> m) {
 331         if (m instanceof EnumMap) {
 332             EnumMap<?, ?> em = (EnumMap<?, ?>)m;
 333             if (em.keyType != keyType) {
 334                 if (em.isEmpty())
 335                     return;
 336                 throw new ClassCastException(em.keyType + " != " + keyType);
 337             }
 338 
 339             for (int i = 0; i < keyUniverse.length; i++) {
 340                 Object emValue = em.vals[i];
 341                 if (emValue != null) {
 342                     if (vals[i] == null)
 343                         size++;
 344                     vals[i] = emValue;
 345                 }
 346             }
 347         } else {
 348             super.putAll(m);
 349         }
 350     }
 351 
 352     /**
 353      * Removes all mappings from this map.
 354      */
 355     public void clear() {
 356         Arrays.fill(vals, null);
 357         size = 0;
 358     }
 359 
 360     // Views
 361 
 362     /**
 363      * This field is initialized to contain an instance of the entry set
 364      * view the first time this view is requested.  The view is stateless,
 365      * so there's no reason to create more than one.
 366      */
 367     private transient Set<Map.Entry<K,V>> entrySet;
 368 
 369     /**
 370      * Returns a {@link Set} view of the keys contained in this map.
 371      * The returned set obeys the general contract outlined in
 372      * {@link Map#keySet()}.  The set's iterator will return the keys
 373      * in their natural order (the order in which the enum constants
 374      * are declared).
 375      *
 376      * @return a set view of the keys contained in this enum map
 377      */
 378     public Set<K> keySet() {
 379         Set<K> ks = keySet;
 380         if (ks == null) {
 381             ks = new KeySet();
 382             keySet = ks;
 383         }
 384         return ks;
 385     }
 386 
 387     private class KeySet extends AbstractSet<K> {
 388         public Iterator<K> iterator() {
 389             return new KeyIterator();
 390         }
 391         public int size() {
 392             return size;
 393         }
 394         public boolean contains(Object o) {
 395             return containsKey(o);
 396         }
 397         public boolean remove(Object o) {
 398             int oldSize = size;
 399             EnumMap.this.remove(o);
 400             return size != oldSize;
 401         }
 402         public void clear() {
 403             EnumMap.this.clear();
 404         }
 405     }
 406 
 407     /**
 408      * Returns a {@link Collection} view of the values contained in this map.
 409      * The returned collection obeys the general contract outlined in
 410      * {@link Map#values()}.  The collection's iterator will return the
 411      * values in the order their corresponding keys appear in map,
 412      * which is their natural order (the order in which the enum constants
 413      * are declared).
 414      *
 415      * @return a collection view of the values contained in this map
 416      */
 417     public Collection<V> values() {
 418         Collection<V> vs = values;
 419         if (vs == null) {
 420             vs = new Values();
 421             values = vs;
 422         }
 423         return vs;
 424     }
 425 
 426     private class Values extends AbstractCollection<V> {
 427         public Iterator<V> iterator() {
 428             return new ValueIterator();
 429         }
 430         public int size() {
 431             return size;
 432         }
 433         public boolean contains(Object o) {
 434             return containsValue(o);
 435         }
 436         public boolean remove(Object o) {
 437             o = maskNull(o);
 438 
 439             for (int i = 0; i < vals.length; i++) {
 440                 if (o.equals(vals[i])) {
 441                     vals[i] = null;
 442                     size--;
 443                     return true;
 444                 }
 445             }
 446             return false;
 447         }
 448         public void clear() {
 449             EnumMap.this.clear();
 450         }
 451     }
 452 
 453     /**
 454      * Returns a {@link Set} view of the mappings contained in this map.
 455      * The returned set obeys the general contract outlined in
 456      * {@link Map#keySet()}.  The set's iterator will return the
 457      * mappings in the order their keys appear in map, which is their
 458      * natural order (the order in which the enum constants are declared).
 459      *
 460      * @return a set view of the mappings contained in this enum map
 461      */
 462     public Set<Map.Entry<K,V>> entrySet() {
 463         Set<Map.Entry<K,V>> es = entrySet;
 464         if (es != null)
 465             return es;
 466         else
 467             return entrySet = new EntrySet();
 468     }
 469 
 470     private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
 471         public Iterator<Map.Entry<K,V>> iterator() {
 472             return new EntryIterator();
 473         }
 474 
 475         public boolean contains(Object o) {
 476             if (!(o instanceof Map.Entry))
 477                 return false;
 478             Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
 479             return containsMapping(entry.getKey(), entry.getValue());
 480         }
 481         public boolean remove(Object o) {
 482             if (!(o instanceof Map.Entry))
 483                 return false;
 484             Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
 485             return removeMapping(entry.getKey(), entry.getValue());
 486         }
 487         public int size() {
 488             return size;
 489         }
 490         public void clear() {
 491             EnumMap.this.clear();
 492         }
 493         public Object[] toArray() {
 494             return fillEntryArray(new Object[size]);
 495         }
 496         @SuppressWarnings("unchecked")
 497         public <T> T[] toArray(T[] a) {
 498             int size = size();
 499             if (a.length < size)
 500                 a = (T[])java.lang.reflect.Array
 501                     .newInstance(a.getClass().getComponentType(), size);
 502             if (a.length > size)
 503                 a[size] = null;
 504             return (T[]) fillEntryArray(a);
 505         }
 506         private Object[] fillEntryArray(Object[] a) {
 507             int j = 0;
 508             for (int i = 0; i < vals.length; i++)
 509                 if (vals[i] != null)
 510                     a[j++] = new AbstractMap.SimpleEntry<>(
 511                         keyUniverse[i], unmaskNull(vals[i]));
 512             return a;
 513         }
 514     }
 515 
 516     private abstract class EnumMapIterator<T> implements Iterator<T> {
 517         // Lower bound on index of next element to return
 518         int index = 0;
 519 
 520         // Index of last returned element, or -1 if none
 521         int lastReturnedIndex = -1;
 522 
 523         public boolean hasNext() {
 524             while (index < vals.length && vals[index] == null)
 525                 index++;
 526             return index != vals.length;
 527         }
 528 
 529         public void remove() {
 530             checkLastReturnedIndex();
 531 
 532             if (vals[lastReturnedIndex] != null) {
 533                 vals[lastReturnedIndex] = null;
 534                 size--;
 535             }
 536             lastReturnedIndex = -1;
 537         }
 538 
 539         private void checkLastReturnedIndex() {
 540             if (lastReturnedIndex < 0)
 541                 throw new IllegalStateException();
 542         }
 543     }
 544 
 545     private class KeyIterator extends EnumMapIterator<K> {
 546         public K next() {
 547             if (!hasNext())
 548                 throw new NoSuchElementException();
 549             lastReturnedIndex = index++;
 550             return keyUniverse[lastReturnedIndex];
 551         }
 552     }
 553 
 554     private class ValueIterator extends EnumMapIterator<V> {
 555         public V next() {
 556             if (!hasNext())
 557                 throw new NoSuchElementException();
 558             lastReturnedIndex = index++;
 559             return unmaskNull(vals[lastReturnedIndex]);
 560         }
 561     }
 562 
 563     private class EntryIterator extends EnumMapIterator<Map.Entry<K,V>> {
 564         private Entry lastReturnedEntry;
 565 
 566         public Map.Entry<K,V> next() {
 567             if (!hasNext())
 568                 throw new NoSuchElementException();
 569             lastReturnedEntry = new Entry(index++);
 570             return lastReturnedEntry;
 571         }
 572 
 573         public void remove() {
 574             lastReturnedIndex =
 575                 ((null == lastReturnedEntry) ? -1 : lastReturnedEntry.index);
 576             super.remove();
 577             lastReturnedEntry.index = lastReturnedIndex;
 578             lastReturnedEntry = null;
 579         }
 580 
 581         private class Entry implements Map.Entry<K,V> {
 582             private int index;
 583 
 584             private Entry(int index) {
 585                 this.index = index;
 586             }
 587 
 588             public K getKey() {
 589                 checkIndexForEntryUse();
 590                 return keyUniverse[index];
 591             }
 592 
 593             public V getValue() {
 594                 checkIndexForEntryUse();
 595                 return unmaskNull(vals[index]);
 596             }
 597 
 598             public V setValue(V value) {
 599                 checkIndexForEntryUse();
 600                 V oldValue = unmaskNull(vals[index]);
 601                 vals[index] = maskNull(value);
 602                 return oldValue;
 603             }
 604 
 605             public boolean equals(Object o) {
 606                 if (index < 0)
 607                     return o == this;
 608 
 609                 if (!(o instanceof Map.Entry))
 610                     return false;
 611 
 612                 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
 613                 V ourValue = unmaskNull(vals[index]);
 614                 Object hisValue = e.getValue();
 615                 return (e.getKey() == keyUniverse[index] &&
 616                         (ourValue == hisValue ||
 617                          (ourValue != null && ourValue.equals(hisValue))));
 618             }
 619 
 620             public int hashCode() {
 621                 if (index < 0)
 622                     return super.hashCode();
 623 
 624                 return entryHashCode(index);
 625             }
 626 
 627             public String toString() {
 628                 if (index < 0)
 629                     return super.toString();
 630 
 631                 return keyUniverse[index] + "="
 632                     + unmaskNull(vals[index]);
 633             }
 634 
 635             private void checkIndexForEntryUse() {
 636                 if (index < 0)
 637                     throw new IllegalStateException("Entry was removed");
 638             }
 639         }
 640     }
 641 
 642     // Comparison and hashing
 643 
 644     /**
 645      * Compares the specified object with this map for equality.  Returns
 646      * {@code true} if the given object is also a map and the two maps
 647      * represent the same mappings, as specified in the {@link
 648      * Map#equals(Object)} contract.
 649      *
 650      * @param o the object to be compared for equality with this map
 651      * @return {@code true} if the specified object is equal to this map
 652      */
 653     public boolean equals(Object o) {
 654         if (this == o)
 655             return true;
 656         if (o instanceof EnumMap)
 657             return equals((EnumMap<?,?>)o);
 658         if (!(o instanceof Map))
 659             return false;
 660 
 661         Map<?,?> m = (Map<?,?>)o;
 662         if (size != m.size())
 663             return false;
 664 
 665         for (int i = 0; i < keyUniverse.length; i++) {
 666             if (null != vals[i]) {
 667                 K key = keyUniverse[i];
 668                 V value = unmaskNull(vals[i]);
 669                 if (null == value) {
 670                     if (!((null == m.get(key)) && m.containsKey(key)))
 671                        return false;
 672                 } else {
 673                    if (!value.equals(m.get(key)))
 674                       return false;
 675                 }
 676             }
 677         }
 678 
 679         return true;
 680     }
 681 
 682     private boolean equals(EnumMap<?,?> em) {
 683         if (em.size != size)
 684             return false;
 685 
 686         if (em.keyType != keyType)
 687             return size == 0;
 688 
 689         // Key types match, compare each value
 690         for (int i = 0; i < keyUniverse.length; i++) {
 691             Object ourValue =    vals[i];
 692             Object hisValue = em.vals[i];
 693             if (hisValue != ourValue &&
 694                 (hisValue == null || !hisValue.equals(ourValue)))
 695                 return false;
 696         }
 697         return true;
 698     }
 699 
 700     /**
 701      * Returns the hash code value for this map.  The hash code of a map is
 702      * defined to be the sum of the hash codes of each entry in the map.
 703      */
 704     public int hashCode() {
 705         int h = 0;
 706 
 707         for (int i = 0; i < keyUniverse.length; i++) {
 708             if (null != vals[i]) {
 709                 h += entryHashCode(i);
 710             }
 711         }
 712 
 713         return h;
 714     }
 715 
 716     private int entryHashCode(int index) {
 717         return (keyUniverse[index].hashCode() ^ vals[index].hashCode());
 718     }
 719 
 720     /**
 721      * Returns a shallow copy of this enum map.  (The values themselves
 722      * are not cloned.
 723      *
 724      * @return a shallow copy of this enum map
 725      */
 726     @SuppressWarnings("unchecked")
 727     public EnumMap<K, V> clone() {
 728         EnumMap<K, V> result = null;
 729         try {
 730             result = (EnumMap<K, V>) super.clone();
 731         } catch(CloneNotSupportedException e) {
 732             throw new AssertionError();
 733         }
 734         result.vals = result.vals.clone();
 735         result.entrySet = null;
 736         return result;
 737     }
 738 
 739     /**
 740      * Throws an exception if e is not of the correct type for this enum set.
 741      */
 742     private void typeCheck(K key) {
 743         Class<?> keyClass = key.getClass();
 744         if (keyClass != keyType && keyClass.getSuperclass() != keyType)
 745             throw new ClassCastException(keyClass + " != " + keyType);
 746     }
 747 
 748     /**
 749      * Returns all of the values comprising K.
 750      * The result is uncloned, cached, and shared by all callers.
 751      */
 752     private static <K extends Enum<K>> K[] getKeyUniverse(Class<K> keyType) {
 753         return SharedSecrets.getJavaLangAccess()
 754                                         .getEnumConstantsShared(keyType);
 755     }
 756 
 757     private static final long serialVersionUID = 458661240069192865L;
 758 
 759     /**
 760      * Save the state of the {@code EnumMap} instance to a stream (i.e.,
 761      * serialize it).
 762      *
 763      * @serialData The <i>size</i> of the enum map (the number of key-value
 764      *             mappings) is emitted (int), followed by the key (Object)
 765      *             and value (Object) for each key-value mapping represented
 766      *             by the enum map.
 767      */
 768     private void writeObject(java.io.ObjectOutputStream s)
 769         throws java.io.IOException
 770     {
 771         // Write out the key type and any hidden stuff
 772         s.defaultWriteObject();
 773 
 774         // Write out size (number of Mappings)
 775         s.writeInt(size);
 776 
 777         // Write out keys and values (alternating)
 778         int entriesToBeWritten = size;
 779         for (int i = 0; entriesToBeWritten > 0; i++) {
 780             if (null != vals[i]) {
 781                 s.writeObject(keyUniverse[i]);
 782                 s.writeObject(unmaskNull(vals[i]));
 783                 entriesToBeWritten--;
 784             }
 785         }
 786     }
 787 
 788     /**
 789      * Reconstitute the {@code EnumMap} instance from a stream (i.e.,
 790      * deserialize it).
 791      */
 792     @SuppressWarnings("unchecked")
 793     private void readObject(java.io.ObjectInputStream s)
 794         throws java.io.IOException, ClassNotFoundException
 795     {
 796         // Read in the key type and any hidden stuff
 797         s.defaultReadObject();
 798 
 799         keyUniverse = getKeyUniverse(keyType);
 800         vals = new Object[keyUniverse.length];
 801 
 802         // Read in size (number of Mappings)
 803         int size = s.readInt();
 804 
 805         // Read the keys and values, and put the mappings in the HashMap
 806         for (int i = 0; i < size; i++) {
 807             K key = (K) s.readObject();
 808             V value = (V) s.readObject();
 809             put(key, value);
 810         }
 811     }
 812 }
--- EOF ---