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NOTE: This class is obsolete.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 Constructor Summary
Dictionary()
Sole constructor.
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Public Method Summary
abstract Enumeration<V> |
elements()
Returns an enumeration of the values in this dictionary.
|
abstract V | |
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
key to the specified
value in this dictionary. |
abstract V | |
abstract int |
size()
Returns the number of entries (distinct keys) in this dictionary.
|
Inherited Method Summary
Public Constructors
public Dictionary ()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Public Methods
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
- an enumeration of the values in this dictionary.
See Also
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 | a key in this dictionary.
null if the key is not mapped to any value in
this dictionary. |
---|
Returns
- the value to which the key is mapped in this dictionary;
Throws
NullPointerException | if the key is null. |
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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
true
if this dictionary maps no keys to values;false
otherwise.
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
- an enumeration of the keys in this dictionary.
See Also
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 | the hashtable key. |
---|---|
value | the value. |
Returns
- the previous value to which the
key
was mapped in this dictionary, ornull
if the key did not have a previous mapping.
Throws
NullPointerException | if the key or
value is null . |
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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 | the key that needs to be removed. |
---|
Returns
- the value to which the
key
had been mapped in this dictionary, ornull
if the key did not have a mapping.
Throws
NullPointerException | if key is null. |
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public abstract int size ()
Returns the number of entries (distinct keys) in this dictionary.
Returns
- the number of keys in this dictionary.