/* * Copyright (c) 1994, 2008, Oracle and/or its affiliates. All rights reserved. * 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 * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * 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. * * 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. */ package java.util; import java.io.*; /** * This class implements a hash table, which maps keys to values. Any * non-null object can be used as a key or as a value.

* * To successfully store and retrieve objects from a hashtable, the * objects used as keys must implement the hashCode * method and the equals method.

* * An instance of Hashtable has two parameters that affect its * performance: initial capacity and load factor. The * capacity is the number of buckets in the hash table, and the * initial capacity is simply the capacity at the time the hash table * is created. Note that the hash table is open: in the case of a "hash * collision", a single bucket stores multiple entries, which must be searched * sequentially. The load factor 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.

* * 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 * Hashtable operations, including get and put).

* * The initial capacity controls a tradeoff between wasted space and the * need for rehash operations, which are time-consuming. * No rehash operations will ever occur if the initial * capacity is greater than the maximum number of entries the * Hashtable will contain divided by its load factor. However, * setting the initial capacity too high can waste space.

* * If many entries are to be made into a Hashtable, * 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.

* * This example creates a hashtable of numbers. It uses the names of * the numbers as keys: *

   {@code
 *   Hashtable numbers
 *     = new Hashtable();
 *   numbers.put("one", 1);
 *   numbers.put("two", 2);
 *   numbers.put("three", 3);}
* *

To retrieve a number, use the following code: *

   {@code
 *   Integer n = numbers.get("two");
 *   if (n != null) {
 *     System.out.println("two = " + n);
 *   }}
* *

The iterators returned by the iterator method of the collections * returned by all of this class's "collection view methods" are * fail-fast: if the Hashtable is structurally modified at any time * after the iterator is created, in any way except through the iterator's own * remove 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 * not fail-fast. * *

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 ConcurrentModificationException on a best-effort basis. * Therefore, it would be wrong to write a program that depended on this * exception for its correctness: the fail-fast behavior of iterators * should be used only to detect bugs. * *

As of the Java 2 platform v1.2, this class was retrofitted to * implement the {@link Map} interface, making it a member of the * * * Java Collections Framework. 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}. * * @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 extends Dictionary implements Map, Cloneable, java.io.Serializable { /** * The hash table data. */ private transient Entry[] table; /** * 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; table = new Entry[initialCapacity]; threshold = (int)(initialCapacity * loadFactor); } /** * 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 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 true if this hashtable maps no keys to values; * false 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 keys() { return this.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 elements() { return this.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. * *

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 true if and only if some key maps to the * value argument in this hashtable as * determined by the equals method; * false otherwise. * @exception NullPointerException if the value is null */ public synchronized boolean contains(Object value) { if (value == null) { throw new NullPointerException(); } Entry tab[] = table; for (int i = tab.length ; i-- > 0 ;) { for (Entry e = tab[i] ; e != null ; e = e.next) { if (e.value.equals(value)) { return true; } } } return false; } /** * Returns true if this hashtable maps one or more keys to this value. * *

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 true if this map maps one or more keys to the * specified value * @throws NullPointerException if the value is null * @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 true if and only if the specified object * is a key in this hashtable, as determined by the * equals method; false otherwise. * @throws NullPointerException if the key is null * @see #contains(Object) */ public synchronized boolean containsKey(Object key) { Entry tab[] = table; int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index] ; e != null ; e = e.next) { 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. * *

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) */ public synchronized V get(Object key) { Entry tab[] = table; int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index] ; e != null ; e = e.next) { if ((e.hash == hash) && e.key.equals(key)) { return e.value; } } return null; } /** * 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; /** * 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. */ protected void rehash() { int oldCapacity = table.length; Entry[] oldMap = table; // 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; } Entry[] newMap = new Entry[newCapacity]; modCount++; threshold = (int)(newCapacity * loadFactor); table = newMap; for (int i = oldCapacity ; i-- > 0 ;) { for (Entry old = oldMap[i] ; old != null ; ) { Entry e = old; old = old.next; int index = (e.hash & 0x7FFFFFFF) % newCapacity; e.next = newMap[index]; newMap[index] = e; } } } /** * Maps the specified key to the specified * value in this hashtable. Neither the key nor the * value can be null.

* * The value can be retrieved by calling the get 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 null if it did not have one * @exception NullPointerException if the key or value is * null * @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. Entry tab[] = table; int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index] ; e != null ; e = e.next) { if ((e.hash == hash) && e.key.equals(key)) { V old = e.value; e.value = value; return old; } } modCount++; if (count >= threshold) { // Rehash the table if the threshold is exceeded rehash(); tab = table; index = (hash & 0x7FFFFFFF) % tab.length; } // Creates the new entry. Entry e = tab[index]; tab[index] = new Entry<>(hash, key, value, e); count++; 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 null if the key did not have a mapping * @throws NullPointerException if the key is null */ public synchronized V remove(Object key) { Entry tab[] = table; int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index], prev = null ; e != null ; prev = e, e = e.next) { 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 t) { for (Map.Entry e : t.entrySet()) put(e.getKey(), e.getValue()); } /** * Clears this hashtable so that it contains no keys. */ public synchronized void clear() { Entry tab[] = table; 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 { Hashtable t = (Hashtable) super.clone(); t.table = new Entry[table.length]; for (int i = table.length ; i-- > 0 ; ) { t.table[i] = (table[i] != null) ? (Entry) table[i].clone() : null; } 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 throw new InternalError(); } } /** * Returns a string representation of this Hashtable object * in the form of a set of entries, enclosed in braces and separated * by the ASCII characters "" (comma and space). Each * entry is rendered as the key, an equals sign =, and the * associated element, where the toString 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> it = entrySet().iterator(); sb.append('{'); for (int i = 0; ; i++) { Map.Entry 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 Enumeration getEnumeration(int type) { if (count == 0) { return Collections.emptyEnumeration(); } else { return new Enumerator<>(type, false); } } private Iterator getIterator(int type) { if (count == 0) { return Collections.emptyIterator(); } else { return new Enumerator<>(type, true); } } // 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. */ private transient volatile Set keySet = null; private transient volatile Set> entrySet = null; private transient volatile Collection values = null; /** * 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 remove operation), the results of * the iteration are undefined. The set supports element removal, * which removes the corresponding mapping from the map, via the * Iterator.remove, Set.remove, * removeAll, retainAll, and clear * operations. It does not support the add or addAll * operations. * * @since 1.2 */ public Set keySet() { if (keySet == null) keySet = Collections.synchronizedSet(new KeySet(), this); return keySet; } private class KeySet extends AbstractSet { public Iterator 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 remove operation, or through the * setValue 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 Iterator.remove, * Set.remove, removeAll, retainAll and * clear operations. It does not support the * add or addAll operations. * * @since 1.2 */ public Set> entrySet() { if (entrySet==null) entrySet = Collections.synchronizedSet(new EntrySet(), this); return entrySet; } private class EntrySet extends AbstractSet> { public Iterator> iterator() { return getIterator(ENTRIES); } public boolean add(Map.Entry o) { return super.add(o); } public boolean contains(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry entry = (Map.Entry)o; Object key = entry.getKey(); Entry[] tab = table; int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index]; e != null; e = e.next) if (e.hash==hash && e.equals(entry)) return true; return false; } public boolean remove(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry entry = (Map.Entry) o; K key = entry.getKey(); Entry[] tab = table; int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index], prev = null; e != null; prev = e, e = e.next) { 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 remove operation), * the results of the iteration are undefined. The collection * supports element removal, which removes the corresponding * mapping from the map, via the Iterator.remove, * Collection.remove, removeAll, * retainAll and clear operations. It does not * support the add or addAll operations. * * @since 1.2 */ public Collection values() { if (values==null) values = Collections.synchronizedCollection(new ValueCollection(), this); return values; } private class ValueCollection extends AbstractCollection { public Iterator 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; Map t = (Map) o; if (t.size() != size()) return false; try { Iterator> i = entrySet().iterator(); while (i.hasNext()) { Map.Entry 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 Entry[] tab = table; for (int i = 0; i < tab.length; i++) for (Entry e = tab[i]; e != null; e = e.next) h += e.key.hashCode() ^ e.value.hashCode(); loadFactor = -loadFactor; // Mark hashCode computation complete return h; } /** * Save the state of the Hashtable to a stream (i.e., serialize it). * * @serialData The capacity of the Hashtable (the length of the * bucket array) is emitted (int), followed by the * size 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. */ private synchronized void writeObject(java.io.ObjectOutputStream s) throws IOException { // Write out the length, threshold, loadfactor s.defaultWriteObject(); // Write out length, count of elements and then the key/value objects s.writeInt(table.length); s.writeInt(count); for (int index = table.length-1; index >= 0; index--) { Entry entry = table[index]; while (entry != null) { s.writeObject(entry.key); s.writeObject(entry.value); entry = entry.next; } } } /** * Reconstitute the Hashtable from a stream (i.e., deserialize it). */ private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException { // Read in the length, threshold, and loadfactor s.defaultReadObject(); // Read the original length of the array and number of elements int origlength = s.readInt(); int elements = s.readInt(); // Compute new size with a bit of room 5% to grow but // no larger than the original size. Make the length // odd if it's large enough, this helps distribute the entries. // Guard against the length ending up zero, that's not valid. int length = (int)(elements * loadFactor) + (elements / 20) + 3; if (length > elements && (length & 1) == 0) length--; if (origlength > 0 && length > origlength) length = origlength; Entry[] table = new Entry[length]; count = 0; // Read the number of elements and then all the key/value objects for (; elements > 0; elements--) { K key = (K)s.readObject(); V value = (V)s.readObject(); // synch could be eliminated for performance reconstitutionPut(table, key, value); } this.table = table; } /** * 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. * *

This differs from the regular put method in several ways. No * checking for rehashing is necessary since the number of elements * initially in the table is known. The modCount is not incremented * because we are creating a new instance. Also, no return value * is needed. */ private void reconstitutionPut(Entry[] tab, K key, V value) 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. int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index] ; e != null ; e = e.next) { if ((e.hash == hash) && e.key.equals(key)) { throw new java.io.StreamCorruptedException(); } } // Creates the new entry. Entry e = tab[index]; tab[index] = new Entry<>(hash, key, value, e); count++; } /** * Hashtable collision list. */ private static class Entry implements Map.Entry { int hash; K key; V value; Entry next; protected Entry(int hash, K key, V value, Entry next) { this.hash = hash; this.key = key; this.value = value; this.next = next; } protected Object clone() { return new Entry<>(hash, key, value, (next==null ? null : (Entry) 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; Map.Entry e = (Map.Entry)o; return (key==null ? e.getKey()==null : key.equals(e.getKey())) && (value==null ? e.getValue()==null : value.equals(e.getValue())); } public int hashCode() { return hash ^ (value==null ? 0 : value.hashCode()); } 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 implements Enumeration, Iterator { Entry[] table = Hashtable.this.table; int index = table.length; Entry entry = null; Entry lastReturned = null; 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() { Entry e = entry; int i = index; Entry[] t = table; /* Use locals for faster loop iteration */ while (e == null && i > 0) { e = t[--i]; } entry = e; index = i; return e != null; } public T nextElement() { Entry et = entry; int i = index; Entry[] t = table; /* Use locals for faster loop iteration */ while (et == null && i > 0) { et = t[--i]; } entry = et; index = i; if (et != null) { Entry e = lastReturned = entry; 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) { Entry[] tab = Hashtable.this.table; int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length; for (Entry e = tab[index], prev = null; e != null; prev = e, e = e.next) { if (e == lastReturned) { modCount++; expectedModCount++; if (prev == null) tab[index] = e.next; else prev.next = e.next; count--; lastReturned = null; return; } } throw new ConcurrentModificationException(); } } } }