java.util.Hashtable<K, V>
Hashtable associates keys with values. Keys and values cannot be null. The
size of the Hashtable is the number of key/value pairs it contains. The
capacity is the number of key/value pairs the Hashtable can hold. The load
factor is a float value which determines how full the Hashtable gets before
expanding the capacity. If the load factor of the Hashtable is exceeded, the
capacity is doubled.
Known Direct Subclasses
Properties |
Properties is a Hashtable where the keys and values must be Strings. |
Known Indirect Subclasses
Summary
Public Constructors
Public Methods
Protected Methods
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
Methods inherited
from interface
java.util.Map
clear,
containsKey,
containsValue,
entrySet,
equals,
get,
hashCode,
isEmpty,
keySet,
put,
putAll,
remove,
size,
values
Details
Public Constructors
public
Hashtable()
Constructs a new Hashtable using the default capacity and load factor.
public
Hashtable(int capacity)
Constructs a new Hashtable using the specified capacity and the default
load factor.
Parameters
capacity
| the initial capacity
|
public
Hashtable(int capacity, float loadFactor)
Constructs a new Hashtable using the specified capacity and load factor.
Parameters
capacity
| the initial capacity |
loadFactor
| the initial load factor
|
public
Hashtable(Map<? extends K, ? extends V> map)
Constructs a new instance of Hashtable containing the mappings from the
specified Map.
Public Methods
public
synchronized
void
clear()
Removes all key/value pairs from this Hashtable, leaving the size zero
and the capacity unchanged.
public
synchronized
Object
clone()
Returns a new Hashtable with the same key/value pairs, capacity and load
factor.
Returns
- a shallow copy of this Hashtable
public
synchronized
boolean
contains(Object value)
Returns if this Hashtable contains the specified object as the value of
at least one of the key/value pairs.
Parameters
value
| the object to look for as a value in this Hashtable |
Returns
- true if object is a value in this Hashtable, false otherwise
public
synchronized
boolean
containsKey(Object key)
Returns if this Hashtable contains the specified object as a key of one
of the key/value pairs.
Parameters
key
| the object to look for as a key in this Hashtable |
Returns
- true if object is a key in this Hashtable, false otherwise
public
boolean
containsValue(Object value)
Searches this Hashtable for the specified value.
Parameters
value
| the object to search for |
Returns
- true if
value
is a value of this Hashtable, false
otherwise
public
synchronized
Enumeration<V>
elements()
Returns an Enumeration on the values of this Hashtable. The results of
the Enumeration may be affected if the contents of this Hashtable are
modified.
Returns
- an Enumeration of the values of this Hashtable
public
Set<Entry<K, V>>
entrySet()
Returns a Set of the mappings contained in this Hashtable. Each element
in the set is a Map.Entry. The set is backed by this Hashtable so changes
to one are reflected by the other. The set does not support adding.
public
synchronized
boolean
equals(Object object)
Compares the specified object to this Hashtable and answer if they are
equal. The object must be an instance of Map and contain the same
key/value pairs.
Parameters
object
| the object to compare with this object |
Returns
- true if the specified object is equal to this Map, false
otherwise
public
synchronized
V
get(Object key)
Returns the value associated with the specified key in this Hashtable.
Parameters
key
| the key of the value returned |
Returns
- the value associated with the specified key, null if the
specified key does not exist
public
synchronized
int
hashCode()
Returns an integer hash code for the receiver. Objects which are equal
answer the same value for this method.
public
synchronized
boolean
isEmpty()
Returns if this Hashtable has no key/value pairs, a size of zero.
Returns
- true if this Hashtable has no key/value pairs, false otherwise
public
Set<K>
keySet()
Returns a Set of the keys contained in this Hashtable. The set is backed
by this Hashtable so changes to one are reflected by the other. The set
does not support adding.
public
synchronized
Enumeration<K>
keys()
Returns an Enumeration on the keys of this Hashtable. The results of the
Enumeration may be affected if the contents of this Hashtable are
modified.
Returns
- an Enumeration of the keys of this Hashtable
public
synchronized
V
put(K key, V value)
Associate the specified value with the specified key in this Hashtable.
If the key already exists, the old value is replaced. The key and value
cannot be null.
Parameters
key
| the key to add |
value
| the value to add |
Returns
- the old value associated with the specified key, null if the key
did not exist
public
synchronized
void
putAll(Map<? extends K, ? extends V> map)
Copies every mapping in the specified Map to this Hashtable.
Parameters
map
| the Map to copy mappings from
|
public
synchronized
V
remove(Object key)
Remove the key/value pair with the specified key from this Hashtable.
Returns
- the value associated with the specified key, null if the
specified key did not exist
public
synchronized
int
size()
Returns the number of key/value pairs in this Hashtable.
Returns
- the number of key/value pairs in this Hashtable
public
synchronized
String
toString()
Returns the string representation of this Hashtable.
Returns
- the string representation of this Hashtable
Returns a Collection of the values contained in this Hashtable. The
collection is backed by this Hashtable so changes to one are reflected by
the other. The collection does not support adding.
Returns
- a Collection of the values
Protected Methods
protected
void
rehash()
Increases the capacity of this Hashtable. This method is sent when the
size of this Hashtable exceeds the load factor.