public
abstract
class
Dictionary
extends Object
| java.lang.Object | |
| ↳ | java.util.Dictionary<K, V> |
 Known Direct Subclasses
Hashtable<K, V>
|
|
Known Indirect Subclasses
|
The Dictionary class is the abstract parent of any
class, such as Hashtable, which maps keys to values.
Every key and every value is an object. In any one Dictionary
object, every key is associated with at most one value. Given a
Dictionary and a key, the associated element can be looked up.
Any non-null object can be used as a key and as a value.
As a rule, the equals method should be used by
implementations of this class to decide if two keys are the same.
NOTE: This class is obsolete. New implementations should implement the Map interface, rather than extending this class.
Public constructors | |
|---|---|
Dictionary()
Sole constructor. |
|
Public methods | |
|---|---|
abstract
Enumeration<V>
|
elements()
Returns an enumeration of the values in this dictionary. |
abstract
V
|
get(Object key)
Returns the value to which the key is mapped in this dictionary. |
abstract
boolean
|
isEmpty()
Tests if this dictionary maps no keys to value. |
abstract
Enumeration<K>
|
keys()
Returns an enumeration of the keys in this dictionary. |
abstract
V
|
put(K key, V value)
Maps the specified |
abstract
V
|
remove(Object key)
Removes the |
abstract
int
|
size()
Returns the number of entries (distinct keys) in this dictionary. |
Inherited methods | |
|---|---|
From
class
java.lang.Object
| |
Dictionary ()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Enumeration<V> elements ()
Returns an enumeration of the values in this dictionary. The general contract for the elements method is that an Enumeration is returned that will generate all the elements contained in entries in this dictionary.
| Returns | |
|---|---|
Enumeration<V> |
an enumeration of the values in this dictionary. |
See also:
V get (Object key)
Returns the value to which the key is mapped in this dictionary. The general contract for the isEmpty method is that if this dictionary contains an entry for the specified key, the associated value is returned; otherwise, null is returned.
| Parameters | |
|---|---|
key |
Object:
a key in this dictionary.
null if the key is not mapped to any value in
this dictionary. |
| Returns | |
|---|---|
V |
the value to which the key is mapped in this dictionary; |
| Throws | |
|---|---|
NullPointerException |
if the key is null. |
See also:
boolean isEmpty ()
Tests if this dictionary maps no keys to value. The general contract for the isEmpty method is that the result is true if and only if this dictionary contains no entries.
| Returns | |
|---|---|
boolean |
true if this dictionary maps no keys to values;
false otherwise.
|
Enumeration<K> keys ()
Returns an enumeration of the keys in this dictionary. The general contract for the keys method is that an Enumeration object is returned that will generate all the keys for which this dictionary contains entries.
| Returns | |
|---|---|
Enumeration<K> |
an enumeration of the keys in this dictionary. |
See also:
Developers
V put (K key,
V value)
Maps the specified key to the specified
value in this dictionary. Neither the key nor the
value can be null.
If this dictionary already contains an entry for the specified key, the value already in this dictionary for that key is returned, after modifying the entry to contain the new element.
If this dictionary does not already have an entry for the specified key, an entry is created for the specified key and value, and null is returned.
The value can be retrieved by calling the
get method with a key that is equal to
the original key.
| Parameters | |
|---|---|
key |
K:
the hashtable key. |
value |
V:
the value. |
| Returns | |
|---|---|
V |
the previous value to which the key was mapped
in this dictionary, or null if the key did not
have a previous mapping. |
| Throws | |
|---|---|
NullPointerException |
if the key or
value is null. |
V remove (Object key)
Removes the key (and its corresponding
value) from this dictionary. This method does nothing
if the key is not in this dictionary.
| Parameters | |
|---|---|
key |
Object:
the key that needs to be removed. |
| Returns | |
|---|---|
V |
the value to which the key had been mapped in this
dictionary, or null if the key did not have a
mapping. |
| Throws | |
|---|---|
NullPointerException |
if key is null. |
int size ()
Returns the number of entries (distinct keys) in this dictionary.
| Returns | |
|---|---|
int |
the number of keys in this dictionary. |