Hashtable.java 49.2 KB
Newer Older
D
duke 已提交
1
/*
2
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
D
duke 已提交
3 4 5 6
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
7
 * published by the Free Software Foundation.  Oracle designates this
D
duke 已提交
8
 * particular file as subject to the "Classpath" exception as provided
9
 * by Oracle in the LICENSE file that accompanied this code.
D
duke 已提交
10 11 12 13 14 15 16 17 18 19 20
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
21 22 23
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
D
duke 已提交
24 25 26
 */

package java.util;
27

D
duke 已提交
28
import java.io.*;
29
import java.util.concurrent.ThreadLocalRandom;
30 31 32
import java.util.function.BiConsumer;
import java.util.function.Function;
import java.util.function.BiFunction;
D
duke 已提交
33 34

/**
35
 * This class implements a hash table, which maps keys to values. Any
D
duke 已提交
36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107
 * non-<code>null</code> object can be used as a key or as a value. <p>
 *
 * To successfully store and retrieve objects from a hashtable, the
 * objects used as keys must implement the <code>hashCode</code>
 * method and the <code>equals</code> method. <p>
 *
 * An instance of <code>Hashtable</code> has two parameters that affect its
 * performance: <i>initial capacity</i> and <i>load factor</i>.  The
 * <i>capacity</i> is the number of <i>buckets</i> in the hash table, and the
 * <i>initial capacity</i> is simply the capacity at the time the hash table
 * is created.  Note that the hash table is <i>open</i>: in the case of a "hash
 * collision", a single bucket stores multiple entries, which must be searched
 * sequentially.  The <i>load factor</i> is a measure of how full the hash
 * table is allowed to get before its capacity is automatically increased.
 * The initial capacity and load factor parameters are merely hints to
 * the implementation.  The exact details as to when and whether the rehash
 * method is invoked are implementation-dependent.<p>
 *
 * Generally, the default load factor (.75) offers a good tradeoff between
 * time and space costs.  Higher values decrease the space overhead but
 * increase the time cost to look up an entry (which is reflected in most
 * <tt>Hashtable</tt> operations, including <tt>get</tt> and <tt>put</tt>).<p>
 *
 * The initial capacity controls a tradeoff between wasted space and the
 * need for <code>rehash</code> operations, which are time-consuming.
 * No <code>rehash</code> operations will <i>ever</i> occur if the initial
 * capacity is greater than the maximum number of entries the
 * <tt>Hashtable</tt> will contain divided by its load factor.  However,
 * setting the initial capacity too high can waste space.<p>
 *
 * If many entries are to be made into a <code>Hashtable</code>,
 * creating it with a sufficiently large capacity may allow the
 * entries to be inserted more efficiently than letting it perform
 * automatic rehashing as needed to grow the table. <p>
 *
 * This example creates a hashtable of numbers. It uses the names of
 * the numbers as keys:
 * <pre>   {@code
 *   Hashtable<String, Integer> numbers
 *     = new Hashtable<String, Integer>();
 *   numbers.put("one", 1);
 *   numbers.put("two", 2);
 *   numbers.put("three", 3);}</pre>
 *
 * <p>To retrieve a number, use the following code:
 * <pre>   {@code
 *   Integer n = numbers.get("two");
 *   if (n != null) {
 *     System.out.println("two = " + n);
 *   }}</pre>
 *
 * <p>The iterators returned by the <tt>iterator</tt> method of the collections
 * returned by all of this class's "collection view methods" are
 * <em>fail-fast</em>: if the Hashtable is structurally modified at any time
 * after the iterator is created, in any way except through the iterator's own
 * <tt>remove</tt> method, the iterator will throw a {@link
 * ConcurrentModificationException}.  Thus, in the face of concurrent
 * modification, the iterator fails quickly and cleanly, rather than risking
 * arbitrary, non-deterministic behavior at an undetermined time in the future.
 * The Enumerations returned by Hashtable's keys and elements methods are
 * <em>not</em> fail-fast.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness: <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>As of the Java 2 platform v1.2, this class was retrofitted to
 * implement the {@link Map} interface, making it a member of the
108 109 110 111 112 113 114 115 116
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 *
 * Java Collections Framework</a>.  Unlike the new collection
 * implementations, {@code Hashtable} is synchronized.  If a
 * thread-safe implementation is not needed, it is recommended to use
 * {@link HashMap} in place of {@code Hashtable}.  If a thread-safe
 * highly-concurrent implementation is desired, then it is recommended
 * to use {@link java.util.concurrent.ConcurrentHashMap} in place of
 * {@code Hashtable}.
D
duke 已提交
117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136
 *
 * @author  Arthur van Hoff
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @see     Object#equals(java.lang.Object)
 * @see     Object#hashCode()
 * @see     Hashtable#rehash()
 * @see     Collection
 * @see     Map
 * @see     HashMap
 * @see     TreeMap
 * @since JDK1.0
 */
public class Hashtable<K,V>
    extends Dictionary<K,V>
    implements Map<K,V>, Cloneable, java.io.Serializable {

    /**
     * The hash table data.
     */
137
    private transient Entry<?,?>[] table;
D
duke 已提交
138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189

    /**
     * The total number of entries in the hash table.
     */
    private transient int count;

    /**
     * The table is rehashed when its size exceeds this threshold.  (The
     * value of this field is (int)(capacity * loadFactor).)
     *
     * @serial
     */
    private int threshold;

    /**
     * The load factor for the hashtable.
     *
     * @serial
     */
    private float loadFactor;

    /**
     * The number of times this Hashtable has been structurally modified
     * Structural modifications are those that change the number of entries in
     * the Hashtable or otherwise modify its internal structure (e.g.,
     * rehash).  This field is used to make iterators on Collection-views of
     * the Hashtable fail-fast.  (See ConcurrentModificationException).
     */
    private transient int modCount = 0;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 1421746759512286392L;

    /**
     * Constructs a new, empty hashtable with the specified initial
     * capacity and the specified load factor.
     *
     * @param      initialCapacity   the initial capacity of the hashtable.
     * @param      loadFactor        the load factor of the hashtable.
     * @exception  IllegalArgumentException  if the initial capacity is less
     *             than zero, or if the load factor is nonpositive.
     */
    public Hashtable(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal Load: "+loadFactor);

        if (initialCapacity==0)
            initialCapacity = 1;
        this.loadFactor = loadFactor;
190
        table = new Entry<?,?>[initialCapacity];
191
        threshold = (int)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
D
duke 已提交
192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295
    }

    /**
     * Constructs a new, empty hashtable with the specified initial capacity
     * and default load factor (0.75).
     *
     * @param     initialCapacity   the initial capacity of the hashtable.
     * @exception IllegalArgumentException if the initial capacity is less
     *              than zero.
     */
    public Hashtable(int initialCapacity) {
        this(initialCapacity, 0.75f);
    }

    /**
     * Constructs a new, empty hashtable with a default initial capacity (11)
     * and load factor (0.75).
     */
    public Hashtable() {
        this(11, 0.75f);
    }

    /**
     * Constructs a new hashtable with the same mappings as the given
     * Map.  The hashtable is created with an initial capacity sufficient to
     * hold the mappings in the given Map and a default load factor (0.75).
     *
     * @param t the map whose mappings are to be placed in this map.
     * @throws NullPointerException if the specified map is null.
     * @since   1.2
     */
    public Hashtable(Map<? extends K, ? extends V> t) {
        this(Math.max(2*t.size(), 11), 0.75f);
        putAll(t);
    }

    /**
     * Returns the number of keys in this hashtable.
     *
     * @return  the number of keys in this hashtable.
     */
    public synchronized int size() {
        return count;
    }

    /**
     * Tests if this hashtable maps no keys to values.
     *
     * @return  <code>true</code> if this hashtable maps no keys to values;
     *          <code>false</code> otherwise.
     */
    public synchronized boolean isEmpty() {
        return count == 0;
    }

    /**
     * Returns an enumeration of the keys in this hashtable.
     *
     * @return  an enumeration of the keys in this hashtable.
     * @see     Enumeration
     * @see     #elements()
     * @see     #keySet()
     * @see     Map
     */
    public synchronized Enumeration<K> keys() {
        return this.<K>getEnumeration(KEYS);
    }

    /**
     * Returns an enumeration of the values in this hashtable.
     * Use the Enumeration methods on the returned object to fetch the elements
     * sequentially.
     *
     * @return  an enumeration of the values in this hashtable.
     * @see     java.util.Enumeration
     * @see     #keys()
     * @see     #values()
     * @see     Map
     */
    public synchronized Enumeration<V> elements() {
        return this.<V>getEnumeration(VALUES);
    }

    /**
     * Tests if some key maps into the specified value in this hashtable.
     * This operation is more expensive than the {@link #containsKey
     * containsKey} method.
     *
     * <p>Note that this method is identical in functionality to
     * {@link #containsValue containsValue}, (which is part of the
     * {@link Map} interface in the collections framework).
     *
     * @param      value   a value to search for
     * @return     <code>true</code> if and only if some key maps to the
     *             <code>value</code> argument in this hashtable as
     *             determined by the <tt>equals</tt> method;
     *             <code>false</code> otherwise.
     * @exception  NullPointerException  if the value is <code>null</code>
     */
    public synchronized boolean contains(Object value) {
        if (value == null) {
            throw new NullPointerException();
        }

296
        Entry<?,?> tab[] = table;
D
duke 已提交
297
        for (int i = tab.length ; i-- > 0 ;) {
298
            for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) {
D
duke 已提交
299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333
                if (e.value.equals(value)) {
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * Returns true if this hashtable maps one or more keys to this value.
     *
     * <p>Note that this method is identical in functionality to {@link
     * #contains contains} (which predates the {@link Map} interface).
     *
     * @param value value whose presence in this hashtable is to be tested
     * @return <tt>true</tt> if this map maps one or more keys to the
     *         specified value
     * @throws NullPointerException  if the value is <code>null</code>
     * @since 1.2
     */
    public boolean containsValue(Object value) {
        return contains(value);
    }

    /**
     * Tests if the specified object is a key in this hashtable.
     *
     * @param   key   possible key
     * @return  <code>true</code> if and only if the specified object
     *          is a key in this hashtable, as determined by the
     *          <tt>equals</tt> method; <code>false</code> otherwise.
     * @throws  NullPointerException  if the key is <code>null</code>
     * @see     #contains(Object)
     */
    public synchronized boolean containsKey(Object key) {
334
        Entry<?,?> tab[] = table;
335
        int hash = key.hashCode();
D
duke 已提交
336
        int index = (hash & 0x7FFFFFFF) % tab.length;
337
        for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
D
duke 已提交
338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359
            if ((e.hash == hash) && e.key.equals(key)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Returns the value to which the specified key is mapped,
     * or {@code null} if this map contains no mapping for the key.
     *
     * <p>More formally, if this map contains a mapping from a key
     * {@code k} to a value {@code v} such that {@code (key.equals(k))},
     * then this method returns {@code v}; otherwise it returns
     * {@code null}.  (There can be at most one such mapping.)
     *
     * @param key the key whose associated value is to be returned
     * @return the value to which the specified key is mapped, or
     *         {@code null} if this map contains no mapping for the key
     * @throws NullPointerException if the specified key is null
     * @see     #put(Object, Object)
     */
360
    @SuppressWarnings("unchecked")
D
duke 已提交
361
    public synchronized V get(Object key) {
362
        Entry<?,?> tab[] = table;
363
        int hash = key.hashCode();
D
duke 已提交
364
        int index = (hash & 0x7FFFFFFF) % tab.length;
365
        for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
D
duke 已提交
366
            if ((e.hash == hash) && e.key.equals(key)) {
367
                return (V)e.value;
D
duke 已提交
368 369 370 371 372
            }
        }
        return null;
    }

373 374 375 376 377 378 379 380
    /**
     * The maximum size of array to allocate.
     * Some VMs reserve some header words in an array.
     * Attempts to allocate larger arrays may result in
     * OutOfMemoryError: Requested array size exceeds VM limit
     */
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

D
duke 已提交
381 382 383 384 385 386 387
    /**
     * Increases the capacity of and internally reorganizes this
     * hashtable, in order to accommodate and access its entries more
     * efficiently.  This method is called automatically when the
     * number of keys in the hashtable exceeds this hashtable's capacity
     * and load factor.
     */
388
    @SuppressWarnings("unchecked")
D
duke 已提交
389 390
    protected void rehash() {
        int oldCapacity = table.length;
391
        Entry<?,?>[] oldMap = table;
D
duke 已提交
392

393 394 395 396 397 398 399 400
        // overflow-conscious code
        int newCapacity = (oldCapacity << 1) + 1;
        if (newCapacity - MAX_ARRAY_SIZE > 0) {
            if (oldCapacity == MAX_ARRAY_SIZE)
                // Keep running with MAX_ARRAY_SIZE buckets
                return;
            newCapacity = MAX_ARRAY_SIZE;
        }
401
        Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];
D
duke 已提交
402 403

        modCount++;
404
        threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
D
duke 已提交
405 406 407
        table = newMap;

        for (int i = oldCapacity ; i-- > 0 ;) {
408
            for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {
D
duke 已提交
409 410 411 412
                Entry<K,V> e = old;
                old = old.next;

                int index = (e.hash & 0x7FFFFFFF) % newCapacity;
413
                e.next = (Entry<K,V>)newMap[index];
D
duke 已提交
414 415 416 417 418
                newMap[index] = e;
            }
        }
    }

419 420 421 422 423 424 425 426 427
    private void addEntry(int hash, K key, V value, int index) {
        modCount++;

        Entry<?,?> tab[] = table;
        if (count >= threshold) {
            // Rehash the table if the threshold is exceeded
            rehash();

            tab = table;
428
            hash = key.hashCode();
429 430 431 432 433 434 435 436 437 438
            index = (hash & 0x7FFFFFFF) % tab.length;
        }

        // Creates the new entry.
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>) tab[index];
        tab[index] = new Entry<>(hash, key, value, e);
        count++;
    }

D
duke 已提交
439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462
    /**
     * Maps the specified <code>key</code> to the specified
     * <code>value</code> in this hashtable. Neither the key nor the
     * value can be <code>null</code>. <p>
     *
     * The value can be retrieved by calling the <code>get</code> method
     * with a key that is equal to the original key.
     *
     * @param      key     the hashtable key
     * @param      value   the value
     * @return     the previous value of the specified key in this hashtable,
     *             or <code>null</code> if it did not have one
     * @exception  NullPointerException  if the key or value is
     *               <code>null</code>
     * @see     Object#equals(Object)
     * @see     #get(Object)
     */
    public synchronized V put(K key, V value) {
        // Make sure the value is not null
        if (value == null) {
            throw new NullPointerException();
        }

        // Makes sure the key is not already in the hashtable.
463
        Entry<?,?> tab[] = table;
464
        int hash = key.hashCode();
D
duke 已提交
465
        int index = (hash & 0x7FFFFFFF) % tab.length;
466 467 468 469 470 471
        @SuppressWarnings("unchecked")
        Entry<K,V> entry = (Entry<K,V>)tab[index];
        for(; entry != null ; entry = entry.next) {
            if ((entry.hash == hash) && entry.key.equals(key)) {
                V old = entry.value;
                entry.value = value;
D
duke 已提交
472 473 474 475
                return old;
            }
        }

476
        addEntry(hash, key, value, index);
D
duke 已提交
477 478 479 480 481 482 483 484 485 486 487 488 489
        return null;
    }

    /**
     * Removes the key (and its corresponding value) from this
     * hashtable. This method does nothing if the key is not in the hashtable.
     *
     * @param   key   the key that needs to be removed
     * @return  the value to which the key had been mapped in this hashtable,
     *          or <code>null</code> if the key did not have a mapping
     * @throws  NullPointerException  if the key is <code>null</code>
     */
    public synchronized V remove(Object key) {
490
        Entry<?,?> tab[] = table;
491
        int hash = key.hashCode();
D
duke 已提交
492
        int index = (hash & 0x7FFFFFFF) % tab.length;
493 494 495
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for(Entry<K,V> prev = null ; e != null ; prev = e, e = e.next) {
D
duke 已提交
496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529
            if ((e.hash == hash) && e.key.equals(key)) {
                modCount++;
                if (prev != null) {
                    prev.next = e.next;
                } else {
                    tab[index] = e.next;
                }
                count--;
                V oldValue = e.value;
                e.value = null;
                return oldValue;
            }
        }
        return null;
    }

    /**
     * Copies all of the mappings from the specified map to this hashtable.
     * These mappings will replace any mappings that this hashtable had for any
     * of the keys currently in the specified map.
     *
     * @param t mappings to be stored in this map
     * @throws NullPointerException if the specified map is null
     * @since 1.2
     */
    public synchronized void putAll(Map<? extends K, ? extends V> t) {
        for (Map.Entry<? extends K, ? extends V> e : t.entrySet())
            put(e.getKey(), e.getValue());
    }

    /**
     * Clears this hashtable so that it contains no keys.
     */
    public synchronized void clear() {
530
        Entry<?,?> tab[] = table;
D
duke 已提交
531 532 533 534 535 536 537 538 539 540 541 542 543 544 545
        modCount++;
        for (int index = tab.length; --index >= 0; )
            tab[index] = null;
        count = 0;
    }

    /**
     * Creates a shallow copy of this hashtable. All the structure of the
     * hashtable itself is copied, but the keys and values are not cloned.
     * This is a relatively expensive operation.
     *
     * @return  a clone of the hashtable
     */
    public synchronized Object clone() {
        try {
546 547
            Hashtable<?,?> t = (Hashtable<?,?>)super.clone();
            t.table = new Entry<?,?>[table.length];
D
duke 已提交
548 549
            for (int i = table.length ; i-- > 0 ; ) {
                t.table[i] = (table[i] != null)
550
                    ? (Entry<?,?>) table[i].clone() : null;
D
duke 已提交
551 552 553 554 555 556 557 558
            }
            t.keySet = null;
            t.entrySet = null;
            t.values = null;
            t.modCount = 0;
            return t;
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
559
            throw new InternalError(e);
D
duke 已提交
560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600
        }
    }

    /**
     * Returns a string representation of this <tt>Hashtable</tt> object
     * in the form of a set of entries, enclosed in braces and separated
     * by the ASCII characters "<tt>,&nbsp;</tt>" (comma and space). Each
     * entry is rendered as the key, an equals sign <tt>=</tt>, and the
     * associated element, where the <tt>toString</tt> method is used to
     * convert the key and element to strings.
     *
     * @return  a string representation of this hashtable
     */
    public synchronized String toString() {
        int max = size() - 1;
        if (max == -1)
            return "{}";

        StringBuilder sb = new StringBuilder();
        Iterator<Map.Entry<K,V>> it = entrySet().iterator();

        sb.append('{');
        for (int i = 0; ; i++) {
            Map.Entry<K,V> e = it.next();
            K key = e.getKey();
            V value = e.getValue();
            sb.append(key   == this ? "(this Map)" : key.toString());
            sb.append('=');
            sb.append(value == this ? "(this Map)" : value.toString());

            if (i == max)
                return sb.append('}').toString();
            sb.append(", ");
        }
    }


    private <T> Enumeration<T> getEnumeration(int type) {
        if (count == 0) {
            return Collections.emptyEnumeration();
        } else {
601
            return new Enumerator<>(type, false);
D
duke 已提交
602 603 604 605 606 607 608
        }
    }

    private <T> Iterator<T> getIterator(int type) {
        if (count == 0) {
            return Collections.emptyIterator();
        } else {
609
            return new Enumerator<>(type, true);
D
duke 已提交
610 611 612 613 614 615 616 617 618 619
        }
    }

    // Views

    /**
     * Each of these fields are initialized to contain an instance of the
     * appropriate view the first time this view is requested.  The views are
     * stateless, so there's no reason to create more than one of each.
     */
620 621 622
    private transient volatile Set<K> keySet;
    private transient volatile Set<Map.Entry<K,V>> entrySet;
    private transient volatile Collection<V> values;
D
duke 已提交
623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696

    /**
     * Returns a {@link Set} view of the keys contained in this map.
     * The set is backed by the map, so changes to the map are
     * reflected in the set, and vice-versa.  If the map is modified
     * while an iteration over the set is in progress (except through
     * the iterator's own <tt>remove</tt> operation), the results of
     * the iteration are undefined.  The set supports element removal,
     * which removes the corresponding mapping from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
     * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
     * operations.  It does not support the <tt>add</tt> or <tt>addAll</tt>
     * operations.
     *
     * @since 1.2
     */
    public Set<K> keySet() {
        if (keySet == null)
            keySet = Collections.synchronizedSet(new KeySet(), this);
        return keySet;
    }

    private class KeySet extends AbstractSet<K> {
        public Iterator<K> iterator() {
            return getIterator(KEYS);
        }
        public int size() {
            return count;
        }
        public boolean contains(Object o) {
            return containsKey(o);
        }
        public boolean remove(Object o) {
            return Hashtable.this.remove(o) != null;
        }
        public void clear() {
            Hashtable.this.clear();
        }
    }

    /**
     * Returns a {@link Set} view of the mappings contained in this map.
     * The set is backed by the map, so changes to the map are
     * reflected in the set, and vice-versa.  If the map is modified
     * while an iteration over the set is in progress (except through
     * the iterator's own <tt>remove</tt> operation, or through the
     * <tt>setValue</tt> operation on a map entry returned by the
     * iterator) the results of the iteration are undefined.  The set
     * supports element removal, which removes the corresponding
     * mapping from the map, via the <tt>Iterator.remove</tt>,
     * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
     * <tt>clear</tt> operations.  It does not support the
     * <tt>add</tt> or <tt>addAll</tt> operations.
     *
     * @since 1.2
     */
    public Set<Map.Entry<K,V>> entrySet() {
        if (entrySet==null)
            entrySet = Collections.synchronizedSet(new EntrySet(), this);
        return entrySet;
    }

    private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
        public Iterator<Map.Entry<K,V>> iterator() {
            return getIterator(ENTRIES);
        }

        public boolean add(Map.Entry<K,V> o) {
            return super.add(o);
        }

        public boolean contains(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
697
            Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
D
duke 已提交
698
            Object key = entry.getKey();
699
            Entry<?,?>[] tab = table;
700
            int hash = key.hashCode();
D
duke 已提交
701 702
            int index = (hash & 0x7FFFFFFF) % tab.length;

703
            for (Entry<?,?> e = tab[index]; e != null; e = e.next)
D
duke 已提交
704 705 706 707 708 709 710 711
                if (e.hash==hash && e.equals(entry))
                    return true;
            return false;
        }

        public boolean remove(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
712 713 714
            Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
            Object key = entry.getKey();
            Entry<?,?>[] tab = table;
715
            int hash = key.hashCode();
D
duke 已提交
716 717
            int index = (hash & 0x7FFFFFFF) % tab.length;

718 719 720
            @SuppressWarnings("unchecked")
            Entry<K,V> e = (Entry<K,V>)tab[index];
            for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
D
duke 已提交
721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798
                if (e.hash==hash && e.equals(entry)) {
                    modCount++;
                    if (prev != null)
                        prev.next = e.next;
                    else
                        tab[index] = e.next;

                    count--;
                    e.value = null;
                    return true;
                }
            }
            return false;
        }

        public int size() {
            return count;
        }

        public void clear() {
            Hashtable.this.clear();
        }
    }

    /**
     * Returns a {@link Collection} view of the values contained in this map.
     * The collection is backed by the map, so changes to the map are
     * reflected in the collection, and vice-versa.  If the map is
     * modified while an iteration over the collection is in progress
     * (except through the iterator's own <tt>remove</tt> operation),
     * the results of the iteration are undefined.  The collection
     * supports element removal, which removes the corresponding
     * mapping from the map, via the <tt>Iterator.remove</tt>,
     * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
     * <tt>retainAll</tt> and <tt>clear</tt> operations.  It does not
     * support the <tt>add</tt> or <tt>addAll</tt> operations.
     *
     * @since 1.2
     */
    public Collection<V> values() {
        if (values==null)
            values = Collections.synchronizedCollection(new ValueCollection(),
                                                        this);
        return values;
    }

    private class ValueCollection extends AbstractCollection<V> {
        public Iterator<V> iterator() {
            return getIterator(VALUES);
        }
        public int size() {
            return count;
        }
        public boolean contains(Object o) {
            return containsValue(o);
        }
        public void clear() {
            Hashtable.this.clear();
        }
    }

    // Comparison and hashing

    /**
     * Compares the specified Object with this Map for equality,
     * as per the definition in the Map interface.
     *
     * @param  o object to be compared for equality with this hashtable
     * @return true if the specified Object is equal to this Map
     * @see Map#equals(Object)
     * @since 1.2
     */
    public synchronized boolean equals(Object o) {
        if (o == this)
            return true;

        if (!(o instanceof Map))
            return false;
799
        Map<?,?> t = (Map<?,?>) o;
D
duke 已提交
800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848
        if (t.size() != size())
            return false;

        try {
            Iterator<Map.Entry<K,V>> i = entrySet().iterator();
            while (i.hasNext()) {
                Map.Entry<K,V> e = i.next();
                K key = e.getKey();
                V value = e.getValue();
                if (value == null) {
                    if (!(t.get(key)==null && t.containsKey(key)))
                        return false;
                } else {
                    if (!value.equals(t.get(key)))
                        return false;
                }
            }
        } catch (ClassCastException unused)   {
            return false;
        } catch (NullPointerException unused) {
            return false;
        }

        return true;
    }

    /**
     * Returns the hash code value for this Map as per the definition in the
     * Map interface.
     *
     * @see Map#hashCode()
     * @since 1.2
     */
    public synchronized int hashCode() {
        /*
         * This code detects the recursion caused by computing the hash code
         * of a self-referential hash table and prevents the stack overflow
         * that would otherwise result.  This allows certain 1.1-era
         * applets with self-referential hash tables to work.  This code
         * abuses the loadFactor field to do double-duty as a hashCode
         * in progress flag, so as not to worsen the space performance.
         * A negative load factor indicates that hash code computation is
         * in progress.
         */
        int h = 0;
        if (count == 0 || loadFactor < 0)
            return h;  // Returns zero

        loadFactor = -loadFactor;  // Mark hashCode computation in progress
849
        Entry<?,?>[] tab = table;
850 851 852 853 854 855 856
        for (Entry<?,?> entry : tab) {
            while (entry != null) {
                h += entry.hashCode();
                entry = entry.next;
            }
        }

D
duke 已提交
857 858 859 860 861
        loadFactor = -loadFactor;  // Mark hashCode computation complete

        return h;
    }

862 863 864 865 866 867
    @Override
    public synchronized V getOrDefault(Object key, V defaultValue) {
        V result = get(key);
        return (null == result) ? defaultValue : result;
    }

868
    @SuppressWarnings("unchecked")
869 870 871 872
    @Override
    public synchronized void forEach(BiConsumer<? super K, ? super V> action) {
        Objects.requireNonNull(action);     // explicit check required in case
                                            // table is empty.
873 874 875 876
        final int expectedModCount = modCount;

        Entry<?, ?>[] tab = table;
        for (Entry<?, ?> entry : tab) {
877 878 879
            while (entry != null) {
                action.accept((K)entry.key, (V)entry.value);
                entry = entry.next;
880 881 882 883

                if (expectedModCount != modCount) {
                    throw new ConcurrentModificationException();
                }
884 885 886 887
            }
        }
    }

888
    @SuppressWarnings("unchecked")
889
    @Override
890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906
    public synchronized void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
        Objects.requireNonNull(function);     // explicit check required in case
                                              // table is empty.
        final int expectedModCount = modCount;

        Entry<K, V>[] tab = (Entry<K, V>[])table;
        for (Entry<K, V> entry : tab) {
            while (entry != null) {
                entry.value = Objects.requireNonNull(
                    function.apply(entry.key, entry.value));
                entry = entry.next;

                if (expectedModCount != modCount) {
                    throw new ConcurrentModificationException();
                }
            }
        }
907 908 909 910 911 912 913 914
    }

    @Override
    public synchronized V putIfAbsent(K key, V value) {
        Objects.requireNonNull(value);

        // Makes sure the key is not already in the hashtable.
        Entry<?,?> tab[] = table;
915
        int hash = key.hashCode();
916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> entry = (Entry<K,V>)tab[index];
        for (; entry != null; entry = entry.next) {
            if ((entry.hash == hash) && entry.key.equals(key)) {
                V old = entry.value;
                if (old == null) {
                    entry.value = value;
                }
                return old;
            }
        }

        addEntry(hash, key, value, index);
        return null;
    }

    @Override
    public synchronized boolean remove(Object key, Object value) {
        Objects.requireNonNull(value);

        Entry<?,?> tab[] = table;
938
        int hash = key.hashCode();
939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if ((e.hash == hash) && e.key.equals(key) && e.value.equals(value)) {
                modCount++;
                if (prev != null) {
                    prev.next = e.next;
                } else {
                    tab[index] = e.next;
                }
                count--;
                e.value = null;
                return true;
            }
        }
        return false;
    }

    @Override
    public synchronized boolean replace(K key, V oldValue, V newValue) {
960 961
        Objects.requireNonNull(oldValue);
        Objects.requireNonNull(newValue);
962
        Entry<?,?> tab[] = table;
963
        int hash = key.hashCode();
964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (; e != null; e = e.next) {
            if ((e.hash == hash) && e.key.equals(key)) {
                if (e.value.equals(oldValue)) {
                    e.value = newValue;
                    return true;
                } else {
                    return false;
                }
            }
        }
        return false;
    }

    @Override
    public synchronized V replace(K key, V value) {
982
        Objects.requireNonNull(value);
983
        Entry<?,?> tab[] = table;
984
        int hash = key.hashCode();
985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (; e != null; e = e.next) {
            if ((e.hash == hash) && e.key.equals(key)) {
                V oldValue = e.value;
                e.value = value;
                return oldValue;
            }
        }
        return null;
    }

    @Override
    public synchronized V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
        Objects.requireNonNull(mappingFunction);

        Entry<?,?> tab[] = table;
1003
        int hash = key.hashCode();
1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (; e != null; e = e.next) {
            if (e.hash == hash && e.key.equals(key)) {
                // Hashtable not accept null value
                return e.value;
            }
        }

        V newValue = mappingFunction.apply(key);
        if (newValue != null) {
            addEntry(hash, key, newValue, index);
        }

        return newValue;
    }

    @Override
1023
    public synchronized V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1024 1025 1026
        Objects.requireNonNull(remappingFunction);

        Entry<?,?> tab[] = table;
1027
        int hash = key.hashCode();
1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if (e.hash == hash && e.key.equals(key)) {
                V newValue = remappingFunction.apply(key, e.value);
                if (newValue == null) {
                    modCount++;
                    if (prev != null) {
                        prev.next = e.next;
                    } else {
                        tab[index] = e.next;
                    }
                    count--;
                } else {
                    e.value = newValue;
                }
                return newValue;
            }
        }
        return null;
    }

    @Override
1052
    public synchronized V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1053 1054 1055
        Objects.requireNonNull(remappingFunction);

        Entry<?,?> tab[] = table;
1056
        int hash = key.hashCode();
1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if (e.hash == hash && Objects.equals(e.key, key)) {
                V newValue = remappingFunction.apply(key, e.value);
                if (newValue == null) {
                    modCount++;
                    if (prev != null) {
                        prev.next = e.next;
                    } else {
                        tab[index] = e.next;
                    }
                    count--;
                } else {
                    e.value = newValue;
                }
                return newValue;
            }
        }

        V newValue = remappingFunction.apply(key, null);
        if (newValue != null) {
            addEntry(hash, key, newValue, index);
        }

        return newValue;
    }

    @Override
1087
    public synchronized V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1088 1089 1090
        Objects.requireNonNull(remappingFunction);

        Entry<?,?> tab[] = table;
1091
        int hash = key.hashCode();
1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if (e.hash == hash && e.key.equals(key)) {
                V newValue = remappingFunction.apply(e.value, value);
                if (newValue == null) {
                    modCount++;
                    if (prev != null) {
                        prev.next = e.next;
                    } else {
                        tab[index] = e.next;
                    }
                    count--;
                } else {
                    e.value = newValue;
                }
                return newValue;
            }
        }

        if (value != null) {
            addEntry(hash, key, value, index);
        }

        return value;
    }

D
duke 已提交
1120 1121 1122 1123 1124 1125 1126 1127 1128 1129
    /**
     * Save the state of the Hashtable to a stream (i.e., serialize it).
     *
     * @serialData The <i>capacity</i> of the Hashtable (the length of the
     *             bucket array) is emitted (int), followed by the
     *             <i>size</i> of the Hashtable (the number of key-value
     *             mappings), followed by the key (Object) and value (Object)
     *             for each key-value mapping represented by the Hashtable
     *             The key-value mappings are emitted in no particular order.
     */
1130 1131 1132 1133 1134
    private void writeObject(java.io.ObjectOutputStream s)
            throws IOException {
        Entry<Object, Object> entryStack = null;

        synchronized (this) {
1135
            // Write out the threshold and loadFactor
1136 1137
            s.defaultWriteObject();

1138
            // Write out the length and count of elements
1139 1140 1141 1142 1143
            s.writeInt(table.length);
            s.writeInt(count);

            // Stack copies of the entries in the table
            for (int index = 0; index < table.length; index++) {
1144
                Entry<?,?> entry = table[index];
1145 1146 1147 1148 1149 1150

                while (entry != null) {
                    entryStack =
                        new Entry<>(0, entry.key, entry.value, entryStack);
                    entry = entry.next;
                }
D
duke 已提交
1151 1152
            }
        }
1153 1154 1155 1156 1157 1158 1159

        // Write out the key/value objects from the stacked entries
        while (entryStack != null) {
            s.writeObject(entryStack.key);
            s.writeObject(entryStack.value);
            entryStack = entryStack.next;
        }
D
duke 已提交
1160 1161 1162 1163 1164 1165 1166 1167
    }

    /**
     * Reconstitute the Hashtable from a stream (i.e., deserialize it).
     */
    private void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException
    {
1168
        // Read in the threshold and loadFactor
D
duke 已提交
1169 1170
        s.defaultReadObject();

1171 1172 1173 1174
        // Validate loadFactor (ignore threshold - it will be re-computed)
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new StreamCorruptedException("Illegal Load: " + loadFactor);

D
duke 已提交
1175 1176 1177 1178
        // Read the original length of the array and number of elements
        int origlength = s.readInt();
        int elements = s.readInt();

1179 1180 1181 1182 1183 1184 1185 1186 1187 1188
        // Validate # of elements
        if (elements < 0)
            throw new StreamCorruptedException("Illegal # of Elements: " + elements);

        // Clamp original length to be more than elements / loadFactor
        // (this is the invariant enforced with auto-growth)
        origlength = Math.max(origlength, (int)(elements / loadFactor) + 1);

        // Compute new length with a bit of room 5% + 3 to grow but
        // no larger than the clamped original length.  Make the length
D
duke 已提交
1189 1190
        // odd if it's large enough, this helps distribute the entries.
        // Guard against the length ending up zero, that's not valid.
1191
        int length = (int)((elements + elements / 20) / loadFactor) + 3;
D
duke 已提交
1192 1193
        if (length > elements && (length & 1) == 0)
            length--;
1194
        length = Math.min(length, origlength);
1195 1196
        table = new Entry<?,?>[length];
        threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
D
duke 已提交
1197 1198 1199 1200
        count = 0;

        // Read the number of elements and then all the key/value objects
        for (; elements > 0; elements--) {
1201 1202 1203 1204
            @SuppressWarnings("unchecked")
                K key = (K)s.readObject();
            @SuppressWarnings("unchecked")
                V value = (V)s.readObject();
1205
            // sync is eliminated for performance
D
duke 已提交
1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216
            reconstitutionPut(table, key, value);
        }
    }

    /**
     * The put method used by readObject. This is provided because put
     * is overridable and should not be called in readObject since the
     * subclass will not yet be initialized.
     *
     * <p>This differs from the regular put method in several ways. No
     * checking for rehashing is necessary since the number of elements
1217 1218 1219
     * initially in the table is known. The modCount is not incremented and
     * there's no synchronization because we are creating a new instance.
     * Also, no return value is needed.
D
duke 已提交
1220
     */
1221
    private void reconstitutionPut(Entry<?,?>[] tab, K key, V value)
D
duke 已提交
1222 1223 1224 1225 1226 1227 1228
        throws StreamCorruptedException
    {
        if (value == null) {
            throw new java.io.StreamCorruptedException();
        }
        // Makes sure the key is not already in the hashtable.
        // This should not happen in deserialized version.
1229
        int hash = key.hashCode();
D
duke 已提交
1230
        int index = (hash & 0x7FFFFFFF) % tab.length;
1231
        for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
D
duke 已提交
1232 1233 1234 1235 1236
            if ((e.hash == hash) && e.key.equals(key)) {
                throw new java.io.StreamCorruptedException();
            }
        }
        // Creates the new entry.
1237 1238
        @SuppressWarnings("unchecked")
            Entry<K,V> e = (Entry<K,V>)tab[index];
1239
        tab[index] = new Entry<>(hash, key, value, e);
D
duke 已提交
1240 1241 1242 1243
        count++;
    }

    /**
1244
     * Hashtable bucket collision list entry
D
duke 已提交
1245 1246
     */
    private static class Entry<K,V> implements Map.Entry<K,V> {
1247
        final int hash;
1248
        final K key;
D
duke 已提交
1249 1250 1251 1252 1253
        V value;
        Entry<K,V> next;

        protected Entry(int hash, K key, V value, Entry<K,V> next) {
            this.hash = hash;
1254
            this.key =  key;
D
duke 已提交
1255 1256 1257 1258
            this.value = value;
            this.next = next;
        }

1259
        @SuppressWarnings("unchecked")
D
duke 已提交
1260
        protected Object clone() {
1261
            return new Entry<>(hash, key, value,
D
duke 已提交
1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286
                                  (next==null ? null : (Entry<K,V>) next.clone()));
        }

        // Map.Entry Ops

        public K getKey() {
            return key;
        }

        public V getValue() {
            return value;
        }

        public V setValue(V value) {
            if (value == null)
                throw new NullPointerException();

            V oldValue = this.value;
            this.value = value;
            return oldValue;
        }

        public boolean equals(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
1287
            Map.Entry<?,?> e = (Map.Entry<?,?>)o;
D
duke 已提交
1288 1289 1290 1291 1292 1293

            return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&
               (value==null ? e.getValue()==null : value.equals(e.getValue()));
        }

        public int hashCode() {
1294
            return hash ^ Objects.hashCode(value);
D
duke 已提交
1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314
        }

        public String toString() {
            return key.toString()+"="+value.toString();
        }
    }

    // Types of Enumerations/Iterations
    private static final int KEYS = 0;
    private static final int VALUES = 1;
    private static final int ENTRIES = 2;

    /**
     * A hashtable enumerator class.  This class implements both the
     * Enumeration and Iterator interfaces, but individual instances
     * can be created with the Iterator methods disabled.  This is necessary
     * to avoid unintentionally increasing the capabilities granted a user
     * by passing an Enumeration.
     */
    private class Enumerator<T> implements Enumeration<T>, Iterator<T> {
1315
        Entry<?,?>[] table = Hashtable.this.table;
D
duke 已提交
1316
        int index = table.length;
1317 1318
        Entry<?,?> entry;
        Entry<?,?> lastReturned;
D
duke 已提交
1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339
        int type;

        /**
         * Indicates whether this Enumerator is serving as an Iterator
         * or an Enumeration.  (true -> Iterator).
         */
        boolean iterator;

        /**
         * The modCount value that the iterator believes that the backing
         * Hashtable should have.  If this expectation is violated, the iterator
         * has detected concurrent modification.
         */
        protected int expectedModCount = modCount;

        Enumerator(int type, boolean iterator) {
            this.type = type;
            this.iterator = iterator;
        }

        public boolean hasMoreElements() {
1340
            Entry<?,?> e = entry;
D
duke 已提交
1341
            int i = index;
1342
            Entry<?,?>[] t = table;
D
duke 已提交
1343 1344 1345 1346 1347 1348 1349 1350 1351
            /* Use locals for faster loop iteration */
            while (e == null && i > 0) {
                e = t[--i];
            }
            entry = e;
            index = i;
            return e != null;
        }

1352
        @SuppressWarnings("unchecked")
D
duke 已提交
1353
        public T nextElement() {
1354
            Entry<?,?> et = entry;
D
duke 已提交
1355
            int i = index;
1356
            Entry<?,?>[] t = table;
D
duke 已提交
1357 1358 1359 1360 1361 1362 1363
            /* Use locals for faster loop iteration */
            while (et == null && i > 0) {
                et = t[--i];
            }
            entry = et;
            index = i;
            if (et != null) {
1364
                Entry<?,?> e = lastReturned = entry;
D
duke 已提交
1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390
                entry = e.next;
                return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
            }
            throw new NoSuchElementException("Hashtable Enumerator");
        }

        // Iterator methods
        public boolean hasNext() {
            return hasMoreElements();
        }

        public T next() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            return nextElement();
        }

        public void remove() {
            if (!iterator)
                throw new UnsupportedOperationException();
            if (lastReturned == null)
                throw new IllegalStateException("Hashtable Enumerator");
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();

            synchronized(Hashtable.this) {
1391
                Entry<?,?>[] tab = Hashtable.this.table;
D
duke 已提交
1392 1393
                int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;

1394 1395 1396
                @SuppressWarnings("unchecked")
                Entry<K,V> e = (Entry<K,V>)tab[index];
                for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
D
duke 已提交
1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413
                    if (e == lastReturned) {
                        modCount++;
                        expectedModCount++;
                        if (prev == null)
                            tab[index] = e.next;
                        else
                            prev.next = e.next;
                        count--;
                        lastReturned = null;
                        return;
                    }
                }
                throw new ConcurrentModificationException();
            }
        }
    }
}