Dictionary
public
abstract
class
Dictionary
extends Object
java.lang.Object | |
↳ | java.util.Dictionary<K, V> |
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NOTE: This class is obsolete.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.
Summary
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 | |
---|---|
Public constructors
Dictionary
public Dictionary ()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Public methods
elements
public abstract 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:
get
public abstract 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:
isEmpty
public abstract 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. |
keys
public abstract 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:
put
public abstract 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 . |
remove
public abstract 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 . |
size
public abstract int size ()
Returns the number of entries (distinct keys) in this dictionary.
Returns | |
---|---|
int |
the number of keys in this dictionary. |