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 java.util.Map.Entry;
  29 import jdk.internal.misc.SharedSecrets;
  30 
  31 /**
  32  * A specialized {@link Map} implementation for use with enum type keys.  All
  33  * of the keys in an enum map must come from a single enum type that is
  34  * specified, explicitly or implicitly, when the map is created.  Enum maps
  35  * are represented internally as arrays.  This representation is extremely
  36  * compact and efficient.
  37  *
  38  * <p>Enum maps are maintained in the <i>natural order</i> of their keys
  39  * (the order in which the enum constants are declared).  This is reflected
  40  * in the iterators returned by the collections views ({@link #keySet()},
  41  * {@link #entrySet()}, and {@link #values()}).
  42  *
  43  * <p>Iterators returned by the collection views are <i>weakly consistent</i>:
  44  * they will never throw {@link ConcurrentModificationException} and they may
  45  * or may not show the effects of any modifications to the map that occur while
  46  * the iteration is in progress.
  47  *
  48  * <p>Null keys are not permitted.  Attempts to insert a null key will
  49  * throw {@link NullPointerException}.  Attempts to test for the
  50  * presence of a null key or to remove one will, however, function properly.
  51  * Null values are permitted.
  52 
  53  * <P>Like most collection implementations {@code EnumMap} is not
  54  * synchronized. If multiple threads access an enum map concurrently, and at
  55  * least one of the threads modifies the map, it should be synchronized
  56  * externally.  This is typically accomplished by synchronizing on some
  57  * object that naturally encapsulates the enum map.  If no such object exists,
  58  * the map should be "wrapped" using the {@link Collections#synchronizedMap}
  59  * method.  This is best done at creation time, to prevent accidental
  60  * unsynchronized access:
  61  *
  62  * <pre>
  63  *     Map&lt;EnumKey, V&gt; m
  64  *         = Collections.synchronizedMap(new EnumMap&lt;EnumKey, V&gt;(...));
  65  * </pre>
  66  *
  67  * <p>Implementation note: All basic operations execute in constant time.
  68  * They are likely (though not guaranteed) to be faster than their
  69  * {@link HashMap} counterparts.
  70  *
  71  * <p>This class is a member of the
  72  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
  73  * Java Collections Framework</a>.
  74  *
  75  * @author Josh Bloch
  76  * @see EnumSet
  77  * @since 1.5
  78  */
  79 public class EnumMap<K extends Enum<K>, V> extends AbstractMap<K, V>
  80     implements java.io.Serializable, Cloneable
  81 {
  82     /**
  83      * The {@code Class} object for the enum type of all the keys of this map.
  84      *
  85      * @serial
  86      */
  87     private final Class<K> keyType;
  88 
  89     /**
  90      * All of the values comprising K.  (Cached for performance.)
  91      */
  92     private transient K[] keyUniverse;
  93 
  94     /**
  95      * Array representation of this map.  The ith element is the value
  96      * to which universe[i] is currently mapped, or null if it isn't
  97      * mapped to anything, or NULL if it's mapped to null.
  98      */
  99     private transient Object[] vals;
 100 
 101     /**
 102      * The number of mappings in this map.
 103      */
 104     private transient int size = 0;
 105 
 106     /**
 107      * Distinguished non-null value for representing null values.
 108      */
 109     private static final Object NULL = new Object() {
 110         public int hashCode() {
 111             return 0;
 112         }
 113 
 114         public String toString() {
 115             return "java.util.EnumMap.NULL";
 116         }
 117     };
 118 
 119     private Object maskNull(Object value) {
 120         return (value == null ? NULL : value);
 121     }
 122 
 123     @SuppressWarnings("unchecked")
 124     private V unmaskNull(Object value) {
 125         return (V)(value == NULL ? null : value);
 126     }
 127 
 128     private static final Enum<?>[] ZERO_LENGTH_ENUM_ARRAY = new Enum<?>[0];
 129 
 130     /**
 131      * Creates an empty enum map with the specified key type.
 132      *
 133      * @param keyType the class object of the key type for this enum map
 134      * @throws NullPointerException if {@code keyType} is null
 135      */
 136     public EnumMap(Class<K> keyType) {
 137         this.keyType = keyType;
 138         keyUniverse = getKeyUniverse(keyType);
 139         vals = new Object[keyUniverse.length];
 140     }
 141 
 142     /**
 143      * Creates an enum map with the same key type as the specified enum
 144      * map, initially containing the same mappings (if any).
 145      *
 146      * @param m the enum map from which to initialize this enum map
 147      * @throws NullPointerException if {@code m} is null
 148      */
 149     public EnumMap(EnumMap<K, ? extends V> m) {
 150         keyType = m.keyType;
 151         keyUniverse = m.keyUniverse;
 152         vals = m.vals.clone();
 153         size = m.size;
 154     }
 155 
 156     /**
 157      * Creates an enum map initialized from the specified map.  If the
 158      * specified map is an {@code EnumMap} instance, this constructor behaves
 159      * identically to {@link #EnumMap(EnumMap)}.  Otherwise, the specified map
 160      * must contain at least one mapping (in order to determine the new
 161      * enum map's key type).
 162      *
 163      * @param m the map from which to initialize this enum map
 164      * @throws IllegalArgumentException if {@code m} is not an
 165      *     {@code EnumMap} instance and contains no mappings
 166      * @throws NullPointerException if {@code m} is null
 167      */
 168     public EnumMap(Map<K, ? extends V> m) {
 169         if (m instanceof EnumMap) {
 170             EnumMap<K, ? extends V> em = (EnumMap<K, ? extends V>) m;
 171             keyType = em.keyType;
 172             keyUniverse = em.keyUniverse;
 173             vals = em.vals.clone();
 174             size = em.size;
 175         } else {
 176             if (m.isEmpty())
 177                 throw new IllegalArgumentException("Specified map is empty");
 178             keyType = m.keySet().iterator().next().getDeclaringClass();
 179             keyUniverse = getKeyUniverse(keyType);
 180             vals = new Object[keyUniverse.length];
 181             putAll(m);
 182         }
 183     }
 184 
 185     // Query Operations
 186 
 187     /**
 188      * Returns the number of key-value mappings in this map.
 189      *
 190      * @return the number of key-value mappings in this map
 191      */
 192     public int size() {
 193         return size;
 194     }
 195 
 196     /**
 197      * Returns {@code true} if this map maps one or more keys to the
 198      * specified value.
 199      *
 200      * @param value the value whose presence in this map is to be tested
 201      * @return {@code true} if this map maps one or more keys to this value
 202      */
 203     public boolean containsValue(Object value) {
 204         value = maskNull(value);
 205 
 206         for (Object val : vals)
 207             if (value.equals(val))
 208                 return true;
 209 
 210         return false;
 211     }
 212 
 213     /**
 214      * Returns {@code true} if this map contains a mapping for the specified
 215      * key.
 216      *
 217      * @param key the key whose presence in this map is to be tested
 218      * @return {@code true} if this map contains a mapping for the specified
 219      *            key
 220      */
 221     public boolean containsKey(Object key) {
 222         return isValidKey(key) && vals[((Enum<?>)key).ordinal()] != null;
 223     }
 224 
 225     private boolean containsMapping(Object key, Object value) {
 226         return isValidKey(key) &&
 227             maskNull(value).equals(vals[((Enum<?>)key).ordinal()]);
 228     }
 229 
 230     /**
 231      * Returns the value to which the specified key is mapped,
 232      * or {@code null} if this map contains no mapping for the key.
 233      *
 234      * <p>More formally, if this map contains a mapping from a key
 235      * {@code k} to a value {@code v} such that {@code (key == k)},
 236      * then this method returns {@code v}; otherwise it returns
 237      * {@code null}.  (There can be at most one such mapping.)
 238      *
 239      * <p>A return value of {@code null} does not <i>necessarily</i>
 240      * indicate that the map contains no mapping for the key; it's also
 241      * possible that the map explicitly maps the key to {@code null}.
 242      * The {@link #containsKey containsKey} operation may be used to
 243      * distinguish these two cases.
 244      */
 245     public V get(Object key) {
 246         return (isValidKey(key) ?
 247                 unmaskNull(vals[((Enum<?>)key).ordinal()]) : null);
 248     }
 249 
 250     // Modification Operations
 251 
 252     /**
 253      * Associates the specified value with the specified key in this map.
 254      * If the map previously contained a mapping for this key, the old
 255      * value is replaced.
 256      *
 257      * @param key the key with which the specified value is to be associated
 258      * @param value the value to be associated with the specified key
 259      *
 260      * @return the previous value associated with specified key, or
 261      *     {@code null} if there was no mapping for key.  (A {@code null}
 262      *     return can also indicate that the map previously associated
 263      *     {@code null} with the specified key.)
 264      * @throws NullPointerException if the specified key is null
 265      */
 266     public V put(K key, V value) {
 267         typeCheck(key);
 268 
 269         int index = key.ordinal();
 270         Object oldValue = vals[index];
 271         vals[index] = maskNull(value);
 272         if (oldValue == null)
 273             size++;
 274         return unmaskNull(oldValue);
 275     }
 276 
 277     /**
 278      * Removes the mapping for this key from this map if present.
 279      *
 280      * @param key the key whose mapping is to be removed from the map
 281      * @return the previous value associated with specified key, or
 282      *     {@code null} if there was no entry for key.  (A {@code null}
 283      *     return can also indicate that the map previously associated
 284      *     {@code null} with the specified key.)
 285      */
 286     public V remove(Object key) {
 287         if (!isValidKey(key))
 288             return null;
 289         int index = ((Enum<?>)key).ordinal();
 290         Object oldValue = vals[index];
 291         vals[index] = null;
 292         if (oldValue != null)
 293             size--;
 294         return unmaskNull(oldValue);
 295     }
 296 
 297     private boolean removeMapping(Object key, Object value) {
 298         if (!isValidKey(key))
 299             return false;
 300         int index = ((Enum<?>)key).ordinal();
 301         if (maskNull(value).equals(vals[index])) {
 302             vals[index] = null;
 303             size--;
 304             return true;
 305         }
 306         return false;
 307     }
 308 
 309     /**
 310      * Returns true if key is of the proper type to be a key in this
 311      * enum map.
 312      */
 313     private boolean isValidKey(Object key) {
 314         if (key == null)
 315             return false;
 316 
 317         // Cheaper than instanceof Enum followed by getDeclaringClass
 318         Class<?> keyClass = key.getClass();
 319         return keyClass == keyType || keyClass.getSuperclass() == keyType;
 320     }
 321 
 322     // Bulk Operations
 323 
 324     /**
 325      * Copies all of the mappings from the specified map to this map.
 326      * These mappings will replace any mappings that this map had for
 327      * any of the keys currently in the specified map.
 328      *
 329      * @param m the mappings to be stored in this map
 330      * @throws NullPointerException the specified map is null, or if
 331      *     one or more keys in the specified map are null
 332      */
 333     public void putAll(Map<? extends K, ? extends V> m) {
 334         if (m instanceof EnumMap) {
 335             EnumMap<?, ?> em = (EnumMap<?, ?>)m;
 336             if (em.keyType != keyType) {
 337                 if (em.isEmpty())
 338                     return;
 339                 throw new ClassCastException(em.keyType + " != " + keyType);
 340             }
 341 
 342             for (int i = 0; i < keyUniverse.length; i++) {
 343                 Object emValue = em.vals[i];
 344                 if (emValue != null) {
 345                     if (vals[i] == null)
 346                         size++;
 347                     vals[i] = emValue;
 348                 }
 349             }
 350         } else {
 351             super.putAll(m);
 352         }
 353     }
 354 
 355     /**
 356      * Removes all mappings from this map.
 357      */
 358     public void clear() {
 359         Arrays.fill(vals, null);
 360         size = 0;
 361     }
 362 
 363     // Views
 364 
 365     /**
 366      * This field is initialized to contain an instance of the entry set
 367      * view the first time this view is requested.  The view is stateless,
 368      * so there's no reason to create more than one.
 369      */
 370     private transient Set<Map.Entry<K,V>> entrySet;
 371 
 372     /**
 373      * Returns a {@link Set} view of the keys contained in this map.
 374      * The returned set obeys the general contract outlined in
 375      * {@link Map#keySet()}.  The set's iterator will return the keys
 376      * in their natural order (the order in which the enum constants
 377      * are declared).
 378      *
 379      * @return a set view of the keys contained in this enum map
 380      */
 381     public Set<K> keySet() {
 382         Set<K> ks = keySet;
 383         if (ks == null) {
 384             ks = new KeySet();
 385             keySet = ks;
 386         }
 387         return ks;
 388     }
 389 
 390     private class KeySet extends AbstractSet<K> {
 391         public Iterator<K> iterator() {
 392             return new KeyIterator();
 393         }
 394         public int size() {
 395             return size;
 396         }
 397         public boolean contains(Object o) {
 398             return containsKey(o);
 399         }
 400         public boolean remove(Object o) {
 401             int oldSize = size;
 402             EnumMap.this.remove(o);
 403             return size != oldSize;
 404         }
 405         public void clear() {
 406             EnumMap.this.clear();
 407         }
 408     }
 409 
 410     /**
 411      * Returns a {@link Collection} view of the values contained in this map.
 412      * The returned collection obeys the general contract outlined in
 413      * {@link Map#values()}.  The collection's iterator will return the
 414      * values in the order their corresponding keys appear in map,
 415      * which is their natural order (the order in which the enum constants
 416      * are declared).
 417      *
 418      * @return a collection view of the values contained in this map
 419      */
 420     public Collection<V> values() {
 421         Collection<V> vs = values;
 422         if (vs == null) {
 423             vs = new Values();
 424             values = vs;
 425         }
 426         return vs;
 427     }
 428 
 429     private class Values extends AbstractCollection<V> {
 430         public Iterator<V> iterator() {
 431             return new ValueIterator();
 432         }
 433         public int size() {
 434             return size;
 435         }
 436         public boolean contains(Object o) {
 437             return containsValue(o);
 438         }
 439         public boolean remove(Object o) {
 440             o = maskNull(o);
 441 
 442             for (int i = 0; i < vals.length; i++) {
 443                 if (o.equals(vals[i])) {
 444                     vals[i] = null;
 445                     size--;
 446                     return true;
 447                 }
 448             }
 449             return false;
 450         }
 451         public void clear() {
 452             EnumMap.this.clear();
 453         }
 454     }
 455 
 456     /**
 457      * Returns a {@link Set} view of the mappings contained in this map.
 458      * The returned set obeys the general contract outlined in
 459      * {@link Map#keySet()}.  The set's iterator will return the
 460      * mappings in the order their keys appear in map, which is their
 461      * natural order (the order in which the enum constants are declared).
 462      *
 463      * @return a set view of the mappings contained in this enum map
 464      */
 465     public Set<Map.Entry<K,V>> entrySet() {
 466         Set<Map.Entry<K,V>> es = entrySet;
 467         if (es != null)
 468             return es;
 469         else
 470             return entrySet = new EntrySet();
 471     }
 472 
 473     private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
 474         public Iterator<Map.Entry<K,V>> iterator() {
 475             return new EntryIterator();
 476         }
 477 
 478         public boolean contains(Object o) {
 479             if (!(o instanceof Map.Entry))
 480                 return false;
 481             Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
 482             return containsMapping(entry.getKey(), entry.getValue());
 483         }
 484         public boolean remove(Object o) {
 485             if (!(o instanceof Map.Entry))
 486                 return false;
 487             Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
 488             return removeMapping(entry.getKey(), entry.getValue());
 489         }
 490         public int size() {
 491             return size;
 492         }
 493         public void clear() {
 494             EnumMap.this.clear();
 495         }
 496         public Object[] toArray() {
 497             return fillEntryArray(new Object[size]);
 498         }
 499         @SuppressWarnings("unchecked")
 500         public <T> T[] toArray(T[] a) {
 501             int size = size();
 502             if (a.length < size)
 503                 a = (T[])java.lang.reflect.Array
 504                     .newInstance(a.getClass().getComponentType(), size);
 505             if (a.length > size)
 506                 a[size] = null;
 507             return (T[]) fillEntryArray(a);
 508         }
 509         private Object[] fillEntryArray(Object[] a) {
 510             int j = 0;
 511             for (int i = 0; i < vals.length; i++)
 512                 if (vals[i] != null)
 513                     a[j++] = new AbstractMap.SimpleEntry<>(
 514                         keyUniverse[i], unmaskNull(vals[i]));
 515             return a;
 516         }
 517     }
 518 
 519     private abstract class EnumMapIterator<T> implements Iterator<T> {
 520         // Lower bound on index of next element to return
 521         int index = 0;
 522 
 523         // Index of last returned element, or -1 if none
 524         int lastReturnedIndex = -1;
 525 
 526         public boolean hasNext() {
 527             while (index < vals.length && vals[index] == null)
 528                 index++;
 529             return index != vals.length;
 530         }
 531 
 532         public void remove() {
 533             checkLastReturnedIndex();
 534 
 535             if (vals[lastReturnedIndex] != null) {
 536                 vals[lastReturnedIndex] = null;
 537                 size--;
 538             }
 539             lastReturnedIndex = -1;
 540         }
 541 
 542         private void checkLastReturnedIndex() {
 543             if (lastReturnedIndex < 0)
 544                 throw new IllegalStateException();
 545         }
 546     }
 547 
 548     private class KeyIterator extends EnumMapIterator<K> {
 549         public K next() {
 550             if (!hasNext())
 551                 throw new NoSuchElementException();
 552             lastReturnedIndex = index++;
 553             return keyUniverse[lastReturnedIndex];
 554         }
 555     }
 556 
 557     private class ValueIterator extends EnumMapIterator<V> {
 558         public V next() {
 559             if (!hasNext())
 560                 throw new NoSuchElementException();
 561             lastReturnedIndex = index++;
 562             return unmaskNull(vals[lastReturnedIndex]);
 563         }
 564     }
 565 
 566     private class EntryIterator extends EnumMapIterator<Map.Entry<K,V>> {
 567         private Entry lastReturnedEntry;
 568 
 569         public Map.Entry<K,V> next() {
 570             if (!hasNext())
 571                 throw new NoSuchElementException();
 572             lastReturnedEntry = new Entry(index++);
 573             return lastReturnedEntry;
 574         }
 575 
 576         public void remove() {
 577             lastReturnedIndex =
 578                 ((null == lastReturnedEntry) ? -1 : lastReturnedEntry.index);
 579             super.remove();
 580             lastReturnedEntry.index = lastReturnedIndex;
 581             lastReturnedEntry = null;
 582         }
 583 
 584         private class Entry implements Map.Entry<K,V> {
 585             private int index;
 586 
 587             private Entry(int index) {
 588                 this.index = index;
 589             }
 590 
 591             public K getKey() {
 592                 checkIndexForEntryUse();
 593                 return keyUniverse[index];
 594             }
 595 
 596             public V getValue() {
 597                 checkIndexForEntryUse();
 598                 return unmaskNull(vals[index]);
 599             }
 600 
 601             public V setValue(V value) {
 602                 checkIndexForEntryUse();
 603                 V oldValue = unmaskNull(vals[index]);
 604                 vals[index] = maskNull(value);
 605                 return oldValue;
 606             }
 607 
 608             public boolean equals(Object o) {
 609                 if (index < 0)
 610                     return o == this;
 611 
 612                 if (!(o instanceof Map.Entry))
 613                     return false;
 614 
 615                 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
 616                 V ourValue = unmaskNull(vals[index]);
 617                 Object hisValue = e.getValue();
 618                 return (e.getKey() == keyUniverse[index] &&
 619                         (ourValue == hisValue ||
 620                          (ourValue != null && ourValue.equals(hisValue))));
 621             }
 622 
 623             public int hashCode() {
 624                 if (index < 0)
 625                     return super.hashCode();
 626 
 627                 return entryHashCode(index);
 628             }
 629 
 630             public String toString() {
 631                 if (index < 0)
 632                     return super.toString();
 633 
 634                 return keyUniverse[index] + "="
 635                     + unmaskNull(vals[index]);
 636             }
 637 
 638             private void checkIndexForEntryUse() {
 639                 if (index < 0)
 640                     throw new IllegalStateException("Entry was removed");
 641             }
 642         }
 643     }
 644 
 645     // Comparison and hashing
 646 
 647     /**
 648      * Compares the specified object with this map for equality.  Returns
 649      * {@code true} if the given object is also a map and the two maps
 650      * represent the same mappings, as specified in the {@link
 651      * Map#equals(Object)} contract.
 652      *
 653      * @param o the object to be compared for equality with this map
 654      * @return {@code true} if the specified object is equal to this map
 655      */
 656     public boolean equals(Object o) {
 657         if (this == o)
 658             return true;
 659         if (o instanceof EnumMap)
 660             return equals((EnumMap<?,?>)o);
 661         if (!(o instanceof Map))
 662             return false;
 663 
 664         Map<?,?> m = (Map<?,?>)o;
 665         if (size != m.size())
 666             return false;
 667 
 668         for (int i = 0; i < keyUniverse.length; i++) {
 669             if (null != vals[i]) {
 670                 K key = keyUniverse[i];
 671                 V value = unmaskNull(vals[i]);
 672                 if (null == value) {
 673                     if (!((null == m.get(key)) && m.containsKey(key)))
 674                        return false;
 675                 } else {
 676                    if (!value.equals(m.get(key)))
 677                       return false;
 678                 }
 679             }
 680         }
 681 
 682         return true;
 683     }
 684 
 685     private boolean equals(EnumMap<?,?> em) {
 686         if (em.size != size)
 687             return false;
 688 
 689         if (em.keyType != keyType)
 690             return size == 0;
 691 
 692         // Key types match, compare each value
 693         for (int i = 0; i < keyUniverse.length; i++) {
 694             Object ourValue =    vals[i];
 695             Object hisValue = em.vals[i];
 696             if (hisValue != ourValue &&
 697                 (hisValue == null || !hisValue.equals(ourValue)))
 698                 return false;
 699         }
 700         return true;
 701     }
 702 
 703     /**
 704      * Returns the hash code value for this map.  The hash code of a map is
 705      * defined to be the sum of the hash codes of each entry in the map.
 706      */
 707     public int hashCode() {
 708         int h = 0;
 709 
 710         for (int i = 0; i < keyUniverse.length; i++) {
 711             if (null != vals[i]) {
 712                 h += entryHashCode(i);
 713             }
 714         }
 715 
 716         return h;
 717     }
 718 
 719     private int entryHashCode(int index) {
 720         return (keyUniverse[index].hashCode() ^ vals[index].hashCode());
 721     }
 722 
 723     /**
 724      * Returns a shallow copy of this enum map.  (The values themselves
 725      * are not cloned.
 726      *
 727      * @return a shallow copy of this enum map
 728      */
 729     @SuppressWarnings("unchecked")
 730     public EnumMap<K, V> clone() {
 731         EnumMap<K, V> result = null;
 732         try {
 733             result = (EnumMap<K, V>) super.clone();
 734         } catch(CloneNotSupportedException e) {
 735             throw new AssertionError();
 736         }
 737         result.vals = result.vals.clone();
 738         result.entrySet = null;
 739         return result;
 740     }
 741 
 742     /**
 743      * Throws an exception if e is not of the correct type for this enum set.
 744      */
 745     private void typeCheck(K key) {
 746         Class<?> keyClass = key.getClass();
 747         if (keyClass != keyType && keyClass.getSuperclass() != keyType)
 748             throw new ClassCastException(keyClass + " != " + keyType);
 749     }
 750 
 751     /**
 752      * Returns all of the values comprising K.
 753      * The result is uncloned, cached, and shared by all callers.
 754      */
 755     private static <K extends Enum<K>> K[] getKeyUniverse(Class<K> keyType) {
 756         return SharedSecrets.getJavaLangAccess()
 757                                         .getEnumConstantsShared(keyType);
 758     }
 759 
 760     private static final long serialVersionUID = 458661240069192865L;
 761 
 762     /**
 763      * Save the state of the {@code EnumMap} instance to a stream (i.e.,
 764      * serialize it).
 765      *
 766      * @serialData The <i>size</i> of the enum map (the number of key-value
 767      *             mappings) is emitted (int), followed by the key (Object)
 768      *             and value (Object) for each key-value mapping represented
 769      *             by the enum map.
 770      */
 771     private void writeObject(java.io.ObjectOutputStream s)
 772         throws java.io.IOException
 773     {
 774         // Write out the key type and any hidden stuff
 775         s.defaultWriteObject();
 776 
 777         // Write out size (number of Mappings)
 778         s.writeInt(size);
 779 
 780         // Write out keys and values (alternating)
 781         int entriesToBeWritten = size;
 782         for (int i = 0; entriesToBeWritten > 0; i++) {
 783             if (null != vals[i]) {
 784                 s.writeObject(keyUniverse[i]);
 785                 s.writeObject(unmaskNull(vals[i]));
 786                 entriesToBeWritten--;
 787             }
 788         }
 789     }
 790 
 791     /**
 792      * Reconstitute the {@code EnumMap} instance from a stream (i.e.,
 793      * deserialize it).
 794      */
 795     @SuppressWarnings("unchecked")
 796     private void readObject(java.io.ObjectInputStream s)
 797         throws java.io.IOException, ClassNotFoundException
 798     {
 799         // Read in the key type and any hidden stuff
 800         s.defaultReadObject();
 801 
 802         keyUniverse = getKeyUniverse(keyType);
 803         vals = new Object[keyUniverse.length];
 804 
 805         // Read in size (number of Mappings)
 806         int size = s.readInt();
 807 
 808         // Read the keys and values, and put the mappings in the HashMap
 809         for (int i = 0; i < size; i++) {
 810             K key = (K) s.readObject();
 811             V value = (V) s.readObject();
 812             put(key, value);
 813         }
 814     }
 815 }
--- EOF ---