java.util.Hashtable
Hashtable
implements the abstract class Dictionary
(§21.4), with
some additional functionality.
public classAHashtable
extends Dictionary implements Cloneable { publicHashtable
(int initialCapacity, float loadFactor); publicHashtable
(int initialCapacity); publicHashtable
(); public StringtoString
(); public Objectclone
(); public intsize
(); public booleanisEmpty
(); public Objectget
(Object key) throws NullPointerException; public Objectput
(Object key, Object value) throws NullPointerException; public Objectremove
(Object key) throws NullPointerException; public Enumerationkeys
(); public Enumerationelements
(); public booleancontains
(Object value); public booleancontainsKey
(Object key); protected voidrehash
(); public voidclear
(); }
Hashtable
has two parameters that affect its efficiency: its capacity and its load factor. The load factor should be between 0.0
and 1.0
. When the number of entries in the hashtable exceeds the product of the load factor and the current capacity, the capacity is increased, using the rehash
method. Larger load factors use memory more efficiently at the expense of larger expected time per lookup. If many entries are to be made in 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.21.5.1 public
Hashtable
(int initialCapacity, float loadFactor)
This constructor initializes a newly created Hashtable
object so that its capacity
is initialCapacity
and its load factor is loadFactor
. Initially, there are no
entries in the table.
21.5.2 public
Hashtable
(int initialCapacity)
This constructor initializes a newly created Hashtable
object so that its capacity
is initialCapacity
and its load factor is 0.75
. Initially, there are no entries in
the table.
21.5.3 public
Hashtable
()
This constructor initializes a newly created Hashtable
object so that its load factor
is 0.75
. Initially, there are no entries in the table.
21.5.4 public String
toString
()
This Hashtable
is represented in string form as 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.
Overrides the toString
method of Object
(§21.2.3).
21.5.5 public Object
clone
()
A copy of this Hashtable
is constructed and returned. All the structure of the
hashtable itself is copied, but the keys and elements are not cloned.
Overrides the clone
method of Object
(§21.2.6).
21.5.6 public int
size
()
Implements the size
method of Dictionary
(§21.4.1).
21.5.7 public boolean
isEmpty
()
Implements the isEmpty
method of Dictionary
(§21.4.2).
21.5.8 public Object
get
(Object key)
Implements the get
method of Dictionary
(§21.4.3).
21.5.9 public Object
put
(Object key, Object value)
Implements the put
method of Dictionary
(§21.4.4).
21.5.10 public Object
remove
(Object key)
Implements the remove
method of Dictionary
(§21.4.5).
21.5.11 public Enumeration
keys
()
Implements the keys
method of Dictionary
(§21.4.6).
21.5.12 public Enumeration
elements
()
Implements the elements
method of Dictionary
(§21.4.7).
21.5.13 public boolean
contains
(Object value)
The result is true
if and only if this Hashtable
contains at least one entry for
which the element is equal to value
, as determined by the equals
method
(§20.1.3).
21.5.14 public boolean
containsKey
(Object key)
The result is true
if and only if this Hashtable
contains an entry for which the
key is equal to key
, as determined by the equals
method (§20.1.3). In other
words, this method produces the same result as the expression:
get(key) != null
21.5.15 protected void
rehash
()
This Hashtable
is increased in capacity and reorganized internally, in order to
accommodate and access its entries more efficiently.
21.5.16 public void
clear
()
The clear
method removes all entries from this Hashtable
.
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