java::util::Hashtable Class Reference

This class implements a hashtable, which maps keys to values. More...

#include <java_util_Hashtable.h>

Inheritance diagram for java::util::Hashtable:

[legend]Collaboration diagram for java::util::Hashtable:

[legend]List of all members.

Public Types
enum	{   xmogDefaultFlags = xmog_base::GLOBAL, xmogMajorVersion = 3, xmogMinorVersion = 2, xmogPatchVersion = 9,   xmogBuildNumber = 2047 }
typedef ::xmog_java_array_template< ::java::util::Hashtable >	array1D
typedef ::xmog_java_array_template< ::xmog_java_array_template< ::java::util::Hashtable > >	array2D
Public Member Functions
virtual void	clear (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Clears this hashtable so that it contains no keys.
virtual ::java::lang::Object	clone (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Creates a shallow copy of this hashtable.
virtual bool	contains (const ::java::lang::Object &value,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Tests if some key maps into the specified value in this hashtable.
virtual bool	containsKey (const ::java::lang::Object &key,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Tests if the specified object is a key in this hashtable.
virtual bool	containsValue (const ::java::lang::Object &value,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns true if this Hashtable maps one or more keys to this value.
virtual ::java::util::Enumeration	elements (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns an enumeration of the values in this hashtable.
virtual ::java::util::Set	entrySet (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns a Set view of the entries contained in this Hashtable.
virtual bool	equals (const ::java::lang::Object &o,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Compares the specified Object with this Map for equality, as per the definition in the Map interface.
virtual ::java::lang::Object	get (const ::java::lang::Object &key,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns the value to which the specified key is mapped in this hashtable.
virtual jint	hashCode (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns the hash code value for this Map as per the definition in the Map interface.
	Hashtable (jint initialCapacity, jfloat loadFactor,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Constructs a new, empty hashtable with the specified initial capacity and the specified load factor.
	Hashtable (::xmog_dummy _use_java_ctor,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Constructs a new, empty hashtable with a default initial capacity (11) and load factor, which is 0.75.
	Hashtable (jint initialCapacity,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Constructs a new, empty hashtable with the specified initial capacity and default load factor, which is 0.75.
	Hashtable (const ::java::util::Map &t,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Constructs a new hashtable with the same mappings as the given Map.
virtual bool	isEmpty (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Tests if this hashtable maps no keys to values.
virtual ::java::util::Enumeration	keys (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns an enumeration of the keys in this hashtable.
virtual ::java::util::Set	keySet (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns a Set view of the keys contained in this Hashtable.
virtual ::java::lang::Object	put (const ::java::lang::Object &key, const ::java::lang::Object &value,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Maps the specified key to the specified value in this hashtable.
virtual void	putAll (const ::java::util::Map &t,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	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.
virtual ::java::lang::Object	remove (const ::java::lang::Object &key,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Removes the key (and its corresponding value) from this hashtable.
virtual jint	size (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns the number of keys in this hashtable.
virtual ::java::lang::String	toString (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	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 "<tt>,&nbsp;</tt>" (comma and space).
virtual ::java::util::Collection	values (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns a Collection view of the values contained in this Hashtable.

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Detailed Description

This class implements a hashtable, 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. When the number of entries in the hashtable exceeds the product of the load factor and the current capacity, the capacity is increased by calling the rehash method.

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:

<blockquote>

                 Hashtable numbers = new Hashtable();
                 numbers.put("one", new Integer(1));
                 numbers.put("two", new Integer(2));
                 numbers.put("three", new Integer(3));

</blockquote>

To retrieve a number, use the following code:

<blockquote>

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

</blockquote>

As of the Java 2 platform v1.2, this class has been retrofitted to implement Map, so that it becomes a part of Java's collection framework. Unlike the new collection implementations, Hashtable is synchronized.

The Iterators returned by the iterator and listIterator methods of the Collections returned by all of Hashtable'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 or add methods, the Iterator will throw a 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 values 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.

This class is a member of the Java Collections Framework.

Author:

Arthur van Hoff

Josh Bloch

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Constructor & Destructor Documentation

java::util::Hashtable::Hashtable (  const ::java::util::Map &  t, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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, which is 0.75. Parameters: t  the map whose mappings are to be placed in this map. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

java::util::Hashtable::Hashtable (  jint  initialCapacity, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Constructs a new, empty hashtable with the specified initial capacity and default load factor, which is 0.75. Parameters: initialCapacity  the initial capacity of the hashtable. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

java::util::Hashtable::Hashtable (  ::xmog_dummy  _use_java_ctor, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Constructs a new, empty hashtable with a default initial capacity (11) and load factor, which is 0.75. Parameters: _use_java_ctor  indicates that you want to delegate to a Java constructor whose natural proxy conflicts with a C++ requirement. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

java::util::Hashtable::Hashtable (  jint  initialCapacity, jfloat  loadFactor, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Constructs a new, empty hashtable with the specified initial capacity and the specified load factor. Parameters: initialCapacity  the initial capacity of the hashtable. loadFactor  the load factor of the hashtable. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

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Member Function Documentation

virtual void java::util::Hashtable::clear (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Clears this hashtable so that it contains no keys. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: Reimplemented from java::util::Map.

virtual ::java::lang::Object java::util::Hashtable::clone (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a clone of the hashtable.

virtual bool java::util::Hashtable::contains (  const ::java::lang::Object &  value, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Tests if some key maps into the specified value in this hashtable. This operation is more expensive than the containsKey method. Note that this method is identical in functionality to containsValue, (which is part of the Map interface in the collections framework). Parameters: value  a value to search for. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: true if and only if some key maps to the value argument in this hashtable as determined by the equals method; false otherwise.

virtual bool java::util::Hashtable::containsKey (  const ::java::lang::Object &  key, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Tests if the specified object is a key in this hashtable. Parameters: key  possible key. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: true if and only if the specified object is a key in this hashtable, as determined by the equals method; false otherwise. Reimplemented from java::util::Map.

virtual bool java::util::Hashtable::containsValue (  const ::java::lang::Object &  value, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Returns true if this Hashtable maps one or more keys to this value. Note that this method is identical in functionality to contains (which predates the Map interface). Parameters: value  value whose presence in this Hashtable is to be tested. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: true if this map maps one or more keys to the specified value. Reimplemented from java::util::Map.

virtual ::java::util::Enumeration java::util::Hashtable::elements (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns an enumeration of the values in this hashtable. Use the Enumeration methods on the returned object to fetch the elements sequentially. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: an enumeration of the values in this hashtable. Reimplemented from java::util::Dictionary.

virtual ::java::util::Set java::util::Hashtable::entrySet (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns a Set view of the entries contained in this Hashtable. Each element in this collection is a Map.Entry. The Set is backed by the Hashtable, so changes to the Hashtable are reflected in the Set, and vice-versa. The Set supports element removal (which removes the corresponding entry from the Hashtable), but not element addition. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a set view of the mappings contained in this map. Reimplemented from java::util::Map.

virtual bool java::util::Hashtable::equals (  const ::java::lang::Object &  o, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Compares the specified Object with this Map for equality, as per the definition in the Map interface. Parameters: o  object to be compared for equality with this Hashtable p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: true if the specified Object is equal to this Map. Reimplemented from java::util::Map.

virtual ::java::lang::Object java::util::Hashtable::get (  const ::java::lang::Object &  key, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns the value to which the specified key is mapped in this hashtable. Parameters: key  a key in the hashtable. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: the value to which the key is mapped in this hashtable; null if the key is not mapped to any value in this hashtable. Reimplemented from java::util::Dictionary.

virtual jint java::util::Hashtable::hashCode (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Returns the hash code value for this Map as per the definition in the Map interface. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: Reimplemented from java::util::Map.

virtual bool java::util::Hashtable::isEmpty (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Tests if this hashtable maps no keys to values. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: true if this hashtable maps no keys to values; false otherwise. Reimplemented from java::util::Dictionary.

virtual ::java::util::Enumeration java::util::Hashtable::keys (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns an enumeration of the keys in this hashtable. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: an enumeration of the keys in this hashtable. Reimplemented from java::util::Dictionary.

virtual ::java::util::Set java::util::Hashtable::keySet (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns a Set view of the keys contained in this Hashtable. The Set is backed by the Hashtable, so changes to the Hashtable are reflected in the Set, and vice-versa. The Set supports element removal (which removes the corresponding entry from the Hashtable), but not element addition. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a set view of the keys contained in this map. Reimplemented from java::util::Map.

virtual ::java::lang::Object java::util::Hashtable::put (  const ::java::lang::Object &  key, const ::java::lang::Object &  value, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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. Parameters: key  the hashtable key. value  the value. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: the previous value of the specified key in this hashtable, or null if it did not have one. Reimplemented from java::util::Dictionary.

virtual void java::util::Hashtable::putAll (  const ::java::util::Map &  t, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

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. Parameters: t  Mappings to be stored in this map. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: Reimplemented from java::util::Map.

virtual ::java::lang::Object java::util::Hashtable::remove (  const ::java::lang::Object &  key, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Removes the key (and its corresponding value) from this hashtable. This method does nothing if the key is not in the hashtable. Parameters: key  the key that needs to be removed. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: the value to which the key had been mapped in this hashtable, or null if the key did not have a mapping. Reimplemented from java::util::Dictionary.

virtual jint java::util::Hashtable::size (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Returns the number of keys in this hashtable. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: the number of keys in this hashtable. Reimplemented from java::util::Dictionary.

virtual ::java::lang::String java::util::Hashtable::toString (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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 "<tt>,&nbsp;</tt>" (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. Overrides to toString method of Object. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a string representation of this hashtable. Reimplemented from java::lang::Object.

virtual ::java::util::Collection java::util::Hashtable::values (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns a Collection view of the values contained in this Hashtable. The Collection is backed by the Hashtable, so changes to the Hashtable are reflected in the Collection, and vice-versa. The Collection supports element removal (which removes the corresponding entry from the Hashtable), but not element addition. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a collection view of the values contained in this map. Reimplemented from java::util::Map.

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The documentation for this class was generated from the following file:

• java_util_Hashtable.h

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