- * - * This implementation of Hashtable uses a hash-bucket approach. That is: - * linear probing and rehashing is avoided; instead, each hashed value maps - * to a simple linked-list which, in the best case, only has one node. - * Assuming a large enough table, low enough load factor, and / or well - * implemented hashCode() methods, Hashtable should provide O(1) - * insertion, deletion, and searching of keys. Hashtable is O(n) in - * the worst case for all of these (if all keys hash to the same bucket). - *
- * - * This is a JDK-1.2 compliant implementation of Hashtable. As such, it - * belongs, partially, to the Collections framework (in that it implements - * Map). For backwards compatibility, it inherits from the obsolete and - * utterly useless Dictionary class. - *
- * - * Being a hybrid of old and new, Hashtable has methods which provide redundant - * capability, but with subtle and even crucial differences. - * For example, one can iterate over various aspects of a Hashtable with - * either an Iterator (which is the JDK-1.2 way of doing things) or with an - * Enumeration. The latter can end up in an undefined state if the Hashtable - * changes while the Enumeration is open. - *
- * - * Unlike HashMap, Hashtable does not accept `null' as a key value. Also, - * all accesses are synchronized: in a single thread environment, this is - * expensive, but in a multi-thread environment, this saves you the effort - * of extra synchronization. However, the old-style enumerators are not - * synchronized, because they can lead to unspecified behavior even if - * they were synchronized. You have been warned. - *
- *
- * The iterators are fail-fast, meaning that any structural
- * modification, except for
- *
- * Every element in Map m will be put into this new Hashtable.
- *
- * @param m a Map whose key / value pairs will be put into
- * the new Hashtable. NOTE: key / value pairs
- * are not cloned in this constructor.
- * @throws NullPointerException if m is null, or if m contains a mapping
- * to or from `null'.
- * @since 1.2
- */
- public Hashtable(Map m)
- {
- this(Math.max(m.size() * 2, DEFAULT_CAPACITY), DEFAULT_LOAD_FACTOR);
- putAllInternal(m);
- }
-
- /**
- * Construct a new Hashtable with a specific inital capacity and
- * default load factor of 0.75.
- *
- * @param initialCapacity the initial capacity of this Hashtable (>= 0)
- * @throws IllegalArgumentException if (initialCapacity < 0)
- */
- public Hashtable(int initialCapacity)
- {
- this(initialCapacity, DEFAULT_LOAD_FACTOR);
- }
-
- /**
- * Construct a new Hashtable with a specific initial capacity and
- * load factor.
- *
- * @param initialCapacity the initial capacity (>= 0)
- * @param loadFactor the load factor (> 0, not NaN)
- * @throws IllegalArgumentException if (initialCapacity < 0) ||
- * ! (loadFactor > 0.0)
- */
- public Hashtable(int initialCapacity, float loadFactor)
- {
- if (initialCapacity < 0)
- throw new IllegalArgumentException("Illegal Capacity: "
- + initialCapacity);
- if (! (loadFactor > 0)) // check for NaN too
- throw new IllegalArgumentException("Illegal Load: " + loadFactor);
-
- if (initialCapacity == 0)
- initialCapacity = 1;
- buckets = new HashEntry[initialCapacity];
- this.loadFactor = loadFactor;
- threshold = (int) (initialCapacity * loadFactor);
- }
-
- /**
- * Returns the number of key-value mappings currently in this hashtable.
- * @return the size
- */
- public synchronized int size()
- {
- return size;
- }
-
- /**
- * Returns true if there are no key-value mappings currently in this table.
- * @return
- *
- * @param value the value to search for in this Hashtable
- * @return true if at least one key maps to the value
- * @throws NullPointerException if
- *
- * NOTE: if the
- *
- * Note that the iterators for all three views, from keySet(), entrySet(),
- * and values(), traverse the hashtable in the same sequence.
- *
- * @return a set view of the entries
- * @see #keySet()
- * @see #values()
- * @see Map.Entry
- * @since 1.2
- */
- public Set entrySet()
- {
- if (entries == null)
- {
- // Create an AbstractSet with custom implementations of those methods
- // that can be overridden easily and efficiently.
- Set r = new AbstractSet()
- {
- public int size()
- {
- return size;
- }
-
- public Iterator iterator()
- {
- return new HashIterator(ENTRIES);
- }
-
- public void clear()
- {
- Hashtable.this.clear();
- }
-
- public boolean contains(Object o)
- {
- return getEntry(o) != null;
- }
-
- public boolean remove(Object o)
- {
- HashEntry e = getEntry(o);
- if (e != null)
- {
- Hashtable.this.remove(e.key);
- return true;
- }
- return false;
- }
- };
- // We must specify the correct object to synchronize upon, hence the
- // use of a non-public API
- entries = new Collections.SynchronizedSet(this, r);
- }
- return entries;
- }
-
- /**
- * Returns true if this Hashtable equals the supplied Object
- *
- * This is not specified, but the new size is twice the current size plus
- * one; this number is not always prime, unfortunately. This implementation
- * is not synchronized, as it is only invoked from synchronized methods.
- */
- protected void rehash()
- {
- HashEntry[] oldBuckets = buckets;
-
- int newcapacity = (buckets.length * 2) + 1;
- threshold = (int) (newcapacity * loadFactor);
- buckets = new HashEntry[newcapacity];
-
- for (int i = oldBuckets.length - 1; i >= 0; i--)
- {
- HashEntry e = oldBuckets[i];
- while (e != null)
- {
- int idx = hash(e.key);
- HashEntry dest = buckets[idx];
-
- if (dest != null)
- {
- while (dest.next != null)
- dest = dest.next;
- dest.next = e;
- }
- else
- {
- buckets[idx] = e;
- }
-
- HashEntry next = e.next;
- e.next = null;
- e = next;
- }
- }
- }
-
- /**
- * Serializes this object to the given stream.
- *
- * @param s the stream to write to
- * @throws IOException if the underlying stream fails
- * @serialData the capacity (int) that is the length of the
- * bucket array, the size (int) of the hash map
- * are emitted first. They are followed by size entries,
- * each consisting of a key (Object) and a value (Object).
- */
- private synchronized void writeObject(ObjectOutputStream s)
- throws IOException
- {
- // Write the threshold and loadFactor fields.
- s.defaultWriteObject();
-
- s.writeInt(buckets.length);
- s.writeInt(size);
- // Since we are already synchronized, and entrySet().iterator()
- // would repeatedly re-lock/release the monitor, we directly use the
- // unsynchronized HashIterator instead.
- Iterator it = new HashIterator(ENTRIES);
- while (it.hasNext())
- {
- HashEntry entry = (HashEntry) it.next();
- s.writeObject(entry.key);
- s.writeObject(entry.value);
- }
- }
-
- /**
- * Deserializes this object from the given stream.
- *
- * @param s the stream to read from
- * @throws ClassNotFoundException if the underlying stream fails
- * @throws IOException if the underlying stream fails
- * @serialData the capacity (int) that is the length of the
- * bucket array, the size (int) of the hash map
- * are emitted first. They are followed by size entries,
- * each consisting of a key (Object) and a value (Object).
- */
- private void readObject(ObjectInputStream s)
- throws IOException, ClassNotFoundException
- {
- // Read the threshold and loadFactor fields.
- s.defaultReadObject();
-
- // Read and use capacity.
- buckets = new HashEntry[s.readInt()];
- int len = s.readInt();
-
- // Read and use key/value pairs.
- // TODO: should we be defensive programmers, and check for illegal nulls?
- while (--len >= 0)
- put(s.readObject(), s.readObject());
- }
-
- /**
- * A class which implements the Iterator interface and is used for
- * iterating over Hashtables.
- * This implementation is parameterized to give a sequential view of
- * keys, values, or entries; it also allows the removal of elements,
- * as per the Javasoft spec. Note that it is not synchronized; this is
- * a performance enhancer since it is never exposed externally and is
- * only used within synchronized blocks above.
- *
- * @author Jon Zeppieri
- */
- private final class HashIterator implements Iterator
- {
- /**
- * The type of this Iterator: {@link #KEYS}, {@link #VALUES},
- * or {@link #ENTRIES}.
- */
- final int type;
- /**
- * The number of modifications to the backing Hashtable that we know about.
- */
- int knownMod = modCount;
- /** The number of elements remaining to be returned by next(). */
- int count = size;
- /** Current index in the physical hash table. */
- int idx = buckets.length;
- /** The last Entry returned by a next() call. */
- HashEntry last;
- /**
- * The next entry that should be returned by next(). It is set to something
- * if we're iterating through a bucket that contains multiple linked
- * entries. It is null if next() needs to find a new bucket.
- */
- HashEntry next;
-
- /**
- * Construct a new HashIterator with the supplied type.
- * @param type {@link #KEYS}, {@link #VALUES}, or {@link #ENTRIES}
- */
- HashIterator(int type)
- {
- this.type = type;
- }
-
- /**
- * Returns true if the Iterator has more elements.
- * @return true if there are more elements
- * @throws ConcurrentModificationException if the hashtable was modified
- */
- public boolean hasNext()
- {
- if (knownMod != modCount)
- throw new ConcurrentModificationException();
- return count > 0;
- }
-
- /**
- * Returns the next element in the Iterator's sequential view.
- * @return the next element
- * @throws ConcurrentModificationException if the hashtable was modified
- * @throws NoSuchElementException if there is none
- */
- public Object next()
- {
- if (knownMod != modCount)
- throw new ConcurrentModificationException();
- if (count == 0)
- throw new NoSuchElementException();
- count--;
- HashEntry e = next;
-
- while (e == null)
- e = buckets[--idx];
-
- next = e.next;
- last = e;
- if (type == VALUES)
- return e.value;
- if (type == KEYS)
- return e.key;
- return e;
- }
-
- /**
- * Removes from the backing Hashtable the last element which was fetched
- * with the remove() called on the iterator
- * itself, cause the iterator to throw a
- * ConcurrentModificationException rather than exhibit
- * non-deterministic behavior.
- *
- * @author Jon Zeppieri
- * @author Warren Levy
- * @author Bryce McKinlay
- * @author Eric Blake rehash().
- * @serial
- */
- private int threshold;
-
- /**
- * Load factor of this Hashtable: used in computing the threshold.
- * @serial
- */
- private final float loadFactor;
-
- /**
- * Array containing the actual key-value mappings.
- */
- // Package visible for use by nested classes.
- transient HashEntry[] buckets;
-
- /**
- * Counts the number of modifications this Hashtable has undergone, used
- * by Iterators to know when to throw ConcurrentModificationExceptions.
- */
- // Package visible for use by nested classes.
- transient int modCount;
-
- /**
- * The size of this Hashtable: denotes the number of key-value pairs.
- */
- // Package visible for use by nested classes.
- transient int size;
-
- /**
- * The cache for {@link #keySet()}.
- */
- private transient Set keys;
-
- /**
- * The cache for {@link #values()}.
- */
- private transient Collection values;
-
- /**
- * The cache for {@link #entrySet()}.
- */
- private transient Set entries;
-
- /**
- * Class to represent an entry in the hash table. Holds a single key-value
- * pair. A Hashtable Entry is identical to a HashMap Entry, except that
- * `null' is not allowed for keys and values.
- */
- private static final class HashEntry extends BasicMapEntry
- {
- /** The next entry in the linked list. */
- HashEntry next;
-
- /**
- * Simple constructor.
- * @param key the key, already guaranteed non-null
- * @param value the value, already guaranteed non-null
- */
- HashEntry(Object key, Object value)
- {
- super(key, value);
- }
-
- /**
- * Resets the value.
- * @param newValue the new value
- * @return the prior value
- * @throws NullPointerException if newVal is null
- */
- public Object setValue(Object newVal)
- {
- if (newVal == null)
- throw new NullPointerException();
- return super.setValue(newVal);
- }
- }
-
- /**
- * Construct a new Hashtable with the default capacity (11) and the default
- * load factor (0.75).
- */
- public Hashtable()
- {
- this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR);
- }
-
- /**
- * Construct a new Hashtable from the given Map, with initial capacity
- * the greater of the size of m or the default of 11.
- * size() == 0
- */
- public synchronized boolean isEmpty()
- {
- return size == 0;
- }
-
- /**
- * Return an enumeration of the keys of this table. There's no point
- * in synchronizing this, as you have already been warned that the
- * enumeration is not specified to be thread-safe.
- *
- * @return the keys
- * @see #elements()
- * @see #keySet()
- */
- public Enumeration keys()
- {
- return new Enumerator(KEYS);
- }
-
- /**
- * Return an enumeration of the values of this table. There's no point
- * in synchronizing this, as you have already been warned that the
- * enumeration is not specified to be thread-safe.
- *
- * @return the values
- * @see #keys()
- * @see #values()
- */
- public Enumeration elements()
- {
- return new Enumerator(VALUES);
- }
-
- /**
- * Returns true if this Hashtable contains a value o,
- * such that o.equals(value). This is the same as
- * containsValue(), and is O(n).
- * value is null
- * @see #containsValue(Object)
- * @see #containsKey(Object)
- */
- public synchronized boolean contains(Object value)
- {
- return containsValue(value);
- }
-
- /**
- * Returns true if this Hashtable contains a value o, such that
- * o.equals(value). This is the new API for the old
- * contains().
- *
- * @param value the value to search for in this Hashtable
- * @return true if at least one key maps to the value
- * @throws NullPointerException if value is null
- * @see #contains(Object)
- * @see #containsKey(Object)
- * @since 1.2
- */
- public boolean containsValue(Object value)
- {
- for (int i = buckets.length - 1; i >= 0; i--)
- {
- HashEntry e = buckets[i];
- while (e != null)
- {
- if (value.equals(e.value))
- return true;
- e = e.next;
- }
- }
-
- // Must throw on null argument even if the table is empty
- if (value == null)
- throw new NullPointerException();
-
- return false;
- }
-
- /**
- * Returns true if the supplied object equals() a key
- * in this Hashtable.
- *
- * @param key the key to search for in this Hashtable
- * @return true if the key is in the table
- * @throws NullPointerException if key is null
- * @see #containsValue(Object)
- */
- public synchronized boolean containsKey(Object key)
- {
- int idx = hash(key);
- HashEntry e = buckets[idx];
- while (e != null)
- {
- if (key.equals(e.key))
- return true;
- e = e.next;
- }
- return false;
- }
-
- /**
- * Return the value in this Hashtable associated with the supplied key,
- * or null if the key maps to nothing.
- *
- * @param key the key for which to fetch an associated value
- * @return what the key maps to, if present
- * @throws NullPointerException if key is null
- * @see #put(Object, Object)
- * @see #containsKey(Object)
- */
- public synchronized Object get(Object key)
- {
- int idx = hash(key);
- HashEntry e = buckets[idx];
- while (e != null)
- {
- if (key.equals(e.key))
- return e.value;
- e = e.next;
- }
- return null;
- }
-
- /**
- * Puts the supplied value into the Map, mapped by the supplied key.
- * Neither parameter may be null. The value may be retrieved by any
- * object which equals() this key.
- *
- * @param key the key used to locate the value
- * @param value the value to be stored in the table
- * @return the prior mapping of the key, or null if there was none
- * @throws NullPointerException if key or value is null
- * @see #get(Object)
- * @see Object#equals(Object)
- */
- public synchronized Object put(Object key, Object value)
- {
- int idx = hash(key);
- HashEntry e = buckets[idx];
-
- // Check if value is null since it is not permitted.
- if (value == null)
- throw new NullPointerException();
-
- while (e != null)
- {
- if (key.equals(e.key))
- {
- // Bypass e.setValue, since we already know value is non-null.
- Object r = e.value;
- e.value = value;
- return r;
- }
- else
- {
- e = e.next;
- }
- }
-
- // At this point, we know we need to add a new entry.
- modCount++;
- if (++size > threshold)
- {
- rehash();
- // Need a new hash value to suit the bigger table.
- idx = hash(key);
- }
-
- e = new HashEntry(key, value);
-
- e.next = buckets[idx];
- buckets[idx] = e;
-
- return null;
- }
-
- /**
- * Removes from the table and returns the value which is mapped by the
- * supplied key. If the key maps to nothing, then the table remains
- * unchanged, and null is returned.
- *
- * @param key the key used to locate the value to remove
- * @return whatever the key mapped to, if present
- */
- public synchronized Object remove(Object key)
- {
- int idx = hash(key);
- HashEntry e = buckets[idx];
- HashEntry last = null;
-
- while (e != null)
- {
- if (key.equals(e.key))
- {
- modCount++;
- if (last == null)
- buckets[idx] = e.next;
- else
- last.next = e.next;
- size--;
- return e.value;
- }
- last = e;
- e = e.next;
- }
- return null;
- }
-
- /**
- * Copies all elements of the given map into this hashtable. However, no
- * mapping can contain null as key or value. If this table already has
- * a mapping for a key, the new mapping replaces the current one.
- *
- * @param m the map to be hashed into this
- * @throws NullPointerException if m is null, or contains null keys or values
- */
- public synchronized void putAll(Map m)
- {
- Iterator itr = m.entrySet().iterator();
-
- for (int msize = m.size(); msize > 0; msize--)
- {
- Map.Entry e = (Map.Entry) itr.next();
- // Optimize in case the Entry is one of our own.
- if (e instanceof BasicMapEntry)
- {
- BasicMapEntry entry = (BasicMapEntry) e;
- put(entry.key, entry.value);
- }
- else
- {
- put(e.getKey(), e.getValue());
- }
- }
- }
-
- /**
- * Clears the hashtable so it has no keys. This is O(1).
- */
- public synchronized void clear()
- {
- if (size > 0)
- {
- modCount++;
- Arrays.fill(buckets, null);
- size = 0;
- }
- }
-
- /**
- * Returns a shallow clone of this Hashtable. The Map itself is cloned,
- * but its contents are not. This is O(n).
- *
- * @return the clone
- */
- public synchronized Object clone()
- {
- Hashtable copy = null;
- try
- {
- copy = (Hashtable) super.clone();
- }
- catch (CloneNotSupportedException x)
- {
- // This is impossible.
- }
- copy.buckets = new HashEntry[buckets.length];
- copy.putAllInternal(this);
- // Clear the caches.
- copy.keys = null;
- copy.values = null;
- copy.entries = null;
- return copy;
- }
-
- /**
- * Converts this Hashtable to a String, surrounded by braces, and with
- * key/value pairs listed with an equals sign between, separated by a
- * comma and space. For example, "{a=1, b=2}".toString() method of any key or value
- * throws an exception, this will fail for the same reason.
- *
- * @return the string representation
- */
- public synchronized String toString()
- {
- // Since we are already synchronized, and entrySet().iterator()
- // would repeatedly re-lock/release the monitor, we directly use the
- // unsynchronized HashIterator instead.
- Iterator entries = new HashIterator(ENTRIES);
- StringBuffer r = new StringBuffer("{");
- for (int pos = size; pos > 0; pos--)
- {
- r.append(entries.next());
- if (pos > 1)
- r.append(", ");
- }
- r.append("}");
- return r.toString();
- }
-
- /**
- * Returns a "set view" of this Hashtable's keys. The set is backed by
- * the hashtable, so changes in one show up in the other. The set supports
- * element removal, but not element addition. The set is properly
- * synchronized on the original hashtable. Sun has not documented the
- * proper interaction of null with this set, but has inconsistent behavior
- * in the JDK. Therefore, in this implementation, contains, remove,
- * containsAll, retainAll, removeAll, and equals just ignore a null key
- * rather than throwing a {@link NullPointerException}.
- *
- * @return a set view of the keys
- * @see #values()
- * @see #entrySet()
- * @since 1.2
- */
- public Set keySet()
- {
- if (keys == null)
- {
- // Create a synchronized AbstractSet with custom implementations of
- // those methods that can be overridden easily and efficiently.
- Set r = new AbstractSet()
- {
- public int size()
- {
- return size;
- }
-
- public Iterator iterator()
- {
- return new HashIterator(KEYS);
- }
-
- public void clear()
- {
- Hashtable.this.clear();
- }
-
- public boolean contains(Object o)
- {
- if (o == null)
- return false;
- return containsKey(o);
- }
-
- public boolean remove(Object o)
- {
- return Hashtable.this.remove(o) != null;
- }
- };
- // We must specify the correct object to synchronize upon, hence the
- // use of a non-public API
- keys = new Collections.SynchronizedSet(this, r);
- }
- return keys;
- }
-
- /**
- * Returns a "collection view" (or "bag view") of this Hashtable's values.
- * The collection is backed by the hashtable, so changes in one show up
- * in the other. The collection supports element removal, but not element
- * addition. The collection is properly synchronized on the original
- * hashtable. Sun has not documented the proper interaction of null with
- * this set, but has inconsistent behavior in the JDK. Therefore, in this
- * implementation, contains, remove, containsAll, retainAll, removeAll, and
- * equals just ignore a null value rather than throwing a
- * {@link NullPointerException}.
- *
- * @return a bag view of the values
- * @see #keySet()
- * @see #entrySet()
- * @since 1.2
- */
- public Collection values()
- {
- if (values == null)
- {
- // We don't bother overriding many of the optional methods, as doing so
- // wouldn't provide any significant performance advantage.
- Collection r = new AbstractCollection()
- {
- public int size()
- {
- return size;
- }
-
- public Iterator iterator()
- {
- return new HashIterator(VALUES);
- }
-
- public void clear()
- {
- Hashtable.this.clear();
- }
- };
- // We must specify the correct object to synchronize upon, hence the
- // use of a non-public API
- values = new Collections.SynchronizedCollection(this, r);
- }
- return values;
- }
-
- /**
- * Returns a "set view" of this Hashtable's entries. The set is backed by
- * the hashtable, so changes in one show up in the other. The set supports
- * element removal, but not element addition. The set is properly
- * synchronized on the original hashtable. Sun has not documented the
- * proper interaction of null with this set, but has inconsistent behavior
- * in the JDK. Therefore, in this implementation, contains, remove,
- * containsAll, retainAll, removeAll, and equals just ignore a null entry,
- * or an entry with a null key or value, rather than throwing a
- * {@link NullPointerException}. However, calling entry.setValue(null)
- * will fail.
- * o.
- * As specified by Map, this is:
- *
- * (o instanceof Map) && entrySet().equals(((Map) o).entrySet());
- *
- *
- * @param o the object to compare to
- * @return true if o is an equal map
- * @since 1.2
- */
- public boolean equals(Object o)
- {
- // no need to synchronize, entrySet().equals() does that
- if (o == this)
- return true;
- if (!(o instanceof Map))
- return false;
-
- return entrySet().equals(((Map) o).entrySet());
- }
-
- /**
- * Returns the hashCode for this Hashtable. As specified by Map, this is
- * the sum of the hashCodes of all of its Map.Entry objects
- *
- * @return the sum of the hashcodes of the entries
- * @since 1.2
- */
- public synchronized int hashCode()
- {
- // Since we are already synchronized, and entrySet().iterator()
- // would repeatedly re-lock/release the monitor, we directly use the
- // unsynchronized HashIterator instead.
- Iterator itr = new HashIterator(ENTRIES);
- int hashcode = 0;
- for (int pos = size; pos > 0; pos--)
- hashcode += itr.next().hashCode();
-
- return hashcode;
- }
-
- /**
- * Helper method that returns an index in the buckets array for `key'
- * based on its hashCode().
- *
- * @param key the key
- * @return the bucket number
- * @throws NullPointerException if key is null
- */
- private int hash(Object key)
- {
- return Math.abs(key.hashCode() % buckets.length);
- }
-
- /**
- * Helper method for entrySet(), which matches both key and value
- * simultaneously. Ignores null, as mentioned in entrySet().
- *
- * @param o the entry to match
- * @return the matching entry, if found, or null
- * @see #entrySet()
- */
- private HashEntry getEntry(Object o)
- {
- if (! (o instanceof Map.Entry))
- return null;
- Object key = ((Map.Entry) o).getKey();
- if (key == null)
- return null;
-
- int idx = hash(key);
- HashEntry e = buckets[idx];
- while (e != null)
- {
- if (o.equals(e))
- return e;
- e = e.next;
- }
- return null;
- }
-
- /**
- * A simplified, more efficient internal implementation of putAll(). The
- * Map constructor and clone() should not call putAll or put, in order to
- * be compatible with the JDK implementation with respect to subclasses.
- *
- * @param m the map to initialize this from
- */
- void putAllInternal(Map m)
- {
- Iterator itr = m.entrySet().iterator();
- int msize = m.size();
- this.size = msize;
-
- for (; msize > 0; msize--)
- {
- Map.Entry e = (Map.Entry) itr.next();
- Object key = e.getKey();
- int idx = hash(key);
- HashEntry he = new HashEntry(key, e.getValue());
- he.next = buckets[idx];
- buckets[idx] = he;
- }
- }
-
- /**
- * Increases the size of the Hashtable and rehashes all keys to new array
- * indices; this is called when the addition of a new value would cause
- * size() > threshold. Note that the existing Entry objects are reused in
- * the new hash table.
- * next() method.
- * @throws ConcurrentModificationException if the hashtable was modified
- * @throws IllegalStateException if called when there is no last element
- */
- public void remove()
- {
- if (knownMod != modCount)
- throw new ConcurrentModificationException();
- if (last == null)
- throw new IllegalStateException();
-
- Hashtable.this.remove(last.key);
- last = null;
- knownMod++;
- }
- } // class HashIterator
-
-
- /**
- * Enumeration view of this Hashtable, providing sequential access to its
- * elements; this implementation is parameterized to provide access either
- * to the keys or to the values in the Hashtable.
- *
- * NOTE: Enumeration is not safe if new elements are put in the table
- * as this could cause a rehash and we'd completely lose our place. Even
- * without a rehash, it is undetermined if a new element added would
- * appear in the enumeration. The spec says nothing about this, but
- * the "Java Class Libraries" book infers that modifications to the
- * hashtable during enumeration causes indeterminate results. Don't do it!
- *
- * @author Jon Zeppieri
- */
- private final class Enumerator implements Enumeration
- {
- /**
- * The type of this Iterator: {@link #KEYS} or {@link #VALUES}.
- */
- final int type;
- /** The number of elements remaining to be returned by next(). */
- int count = size;
- /** Current index in the physical hash table. */
- int idx = buckets.length;
- /**
- * Entry which will be returned by the next nextElement() call. It is
- * set if we are iterating through a bucket with multiple entries, or null
- * if we must look in the next bucket.
- */
- HashEntry next;
-
- /**
- * Construct the enumeration.
- * @param type either {@link #KEYS} or {@link #VALUES}.
- */
- Enumerator(int type)
- {
- this.type = type;
- }
-
- /**
- * Checks whether more elements remain in the enumeration.
- * @return true if nextElement() will not fail.
- */
- public boolean hasMoreElements()
- {
- return count > 0;
- }
-
- /**
- * Returns the next element.
- * @return the next element
- * @throws NoSuchElementException if there is none.
- */
- public Object nextElement()
- {
- if (count == 0)
- throw new NoSuchElementException("Hashtable Enumerator");
- count--;
- HashEntry e = next;
-
- while (e == null)
- e = buckets[--idx];
-
- next = e.next;
- return type == VALUES ? e.value : e.key;
- }
- } // class Enumerator
-}