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	/*
	* Copyright (c) 1994, 2017, 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.*;
	import java.util.concurrent.ThreadLocalRandom;
	import java.util.function.BiConsumer;
	import java.util.function.Function;
	import java.util.function.BiFunction;
	import sun.misc.SharedSecrets;

	/**
	* This class implements a hash table, which maps keys to values. Any
	* 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
	* <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}.
	*
	* @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.
	*/
	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)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
	}

	/**
	* 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();
	}

	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.
	*
	* <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) {
	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.
	*
	* <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)
	*/
	@SuppressWarnings("unchecked")
	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 (V)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.
	*/
	@SuppressWarnings("unchecked")
	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)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
	table = newMap;

	for (int i = oldCapacity ; i-- > 0 ;) {
	for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {
	Entry<K,V> e = old;
	old = old.next;

	int index = (e.hash & 0x7FFFFFFF) % newCapacity;
	e.next = (Entry<K,V>)newMap[index];
	newMap[index] = e;
	}
	}
	}

	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;
	hash = key.hashCode();
	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++;
	}

	/**
	* 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.
	Entry<?,?> tab[] = table;
	int hash = key.hashCode();
	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;
	entry.value = value;
	return old;
	}
	}

	addEntry(hash, key, value, index);
	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) {
	Entry<?,?> tab[] = table;
	int hash = key.hashCode();
	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)) {
	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() {
	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(e);
	}
	}

	/**
	* 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>, </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 {
	return new Enumerator<>(type, false);
	}
	}

	private <T> Iterator<T> 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<K> keySet;
	private transient volatile Set<Map.Entry<K,V>> entrySet;
	private transient volatile Collection<V> values;

	/**
	* 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;
	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;
	Object key = entry.getKey();
	Entry<?,?>[] tab = table;
	int hash = key.hashCode();
	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.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;
	Map<?,?> t = (Map<?,?>) o;
	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
	Entry<?,?>[] tab = table;
	for (Entry<?,?> entry : tab) {
	while (entry != null) {
	h += entry.hashCode();
	entry = entry.next;
	}
	}

	loadFactor = -loadFactor; // Mark hashCode computation complete

	return h;
	}

	@Override
	public synchronized V getOrDefault(Object key, V defaultValue) {
	V result = get(key);
	return (null == result) ? defaultValue : result;
	}

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

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

	if (expectedModCount != modCount) {
	throw new ConcurrentModificationException();
	}
	}
	}
	}

	@SuppressWarnings("unchecked")
	@Override
	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();
	}
	}
	}
	}

	@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;
	int hash = key.hashCode();
	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;
	int hash = key.hashCode();
	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) {
	Objects.requireNonNull(oldValue);
	Objects.requireNonNull(newValue);
	Entry<?,?> tab[] = table;
	int hash = key.hashCode();
	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) {
	Objects.requireNonNull(value);
	Entry<?,?> tab[] = table;
	int hash = key.hashCode();
	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;
	int hash = key.hashCode();
	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
	public synchronized V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	Objects.requireNonNull(remappingFunction);

	Entry<?,?> tab[] = table;
	int hash = key.hashCode();
	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
	public synchronized V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	Objects.requireNonNull(remappingFunction);

	Entry<?,?> tab[] = table;
	int hash = key.hashCode();
	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
	public synchronized V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
	Objects.requireNonNull(remappingFunction);

	Entry<?,?> tab[] = table;
	int hash = key.hashCode();
	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;
	}

	/**
	* 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.
	*/
	private void writeObject(java.io.ObjectOutputStream s)
	throws IOException {
	Entry<Object, Object> entryStack = null;

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

	// Write out the length and count of elements
	s.writeInt(table.length);
	s.writeInt(count);

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

	while (entry != null) {
	entryStack =
	new Entry<>(0, entry.key, entry.value, entryStack);
	entry = entry.next;
	}
	}
	}

	// Write out the key/value objects from the stacked entries
	while (entryStack != null) {
	s.writeObject(entryStack.key);
	s.writeObject(entryStack.value);
	entryStack = entryStack.next;
	}
	}

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

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

	// Read the original length of the array and number of elements
	int origlength = s.readInt();
	int elements = s.readInt();

	// 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
	// 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 + elements / 20) / loadFactor) + 3;
	if (length > elements && (length & 1) == 0)
	length--;
	length = Math.min(length, origlength);

	if (length < 0) { // overflow
	length = origlength;
	}

	// Check Map.Entry[].class since it's the nearest public type to
	// what we're actually creating.
	SharedSecrets.getJavaOISAccess().checkArray(s, Map.Entry[].class, length);
	table = new Entry<?,?>[length];
	threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
	count = 0;

	// Read the number of elements and then all the key/value objects
	for (; elements > 0; elements--) {
	@SuppressWarnings("unchecked")
	K key = (K)s.readObject();
	@SuppressWarnings("unchecked")
	V value = (V)s.readObject();
	// sync is eliminated for performance
	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
	* 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.
	*/
	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.
	@SuppressWarnings("unchecked")
	Entry<K,V> e = (Entry<K,V>)tab[index];
	tab[index] = new Entry<>(hash, key, value, e);
	count++;
	}

	/**
	* Hashtable bucket collision list entry
	*/
	private static class Entry<K,V> implements Map.Entry<K,V> {
	final int hash;
	final K key;
	V value;
	Entry<K,V> next;

	protected Entry(int hash, K key, V value, Entry<K,V> next) {
	this.hash = hash;
	this.key = key;
	this.value = value;
	this.next = next;
	}

	@SuppressWarnings("unchecked")
	protected Object clone() {
	return new Entry<>(hash, key, value,
	(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;
	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 ^ Objects.hashCode(value);
	}

	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> {
	Entry<?,?>[] table = Hashtable.this.table;
	int index = table.length;
	Entry<?,?> entry;
	Entry<?,?> lastReturned;
	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;
	}

	@SuppressWarnings("unchecked")
	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;

	@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 == lastReturned) {
	modCount++;
	expectedModCount++;
	if (prev == null)
	tab[index] = e.next;
	else
	prev.next = e.next;
	count--;
	lastReturned = null;
	return;
	}
	}
	throw new ConcurrentModificationException();
	}
	}
	}
	}

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