java.lang.Object
java.util.Dictionary<K,V>
- Direct Known Subclasses:
Hashtable
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NOTE: This class is obsolete.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.
- Since:
- 1.0
- See Also:
-
Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionabstract Enumeration<V>
elements()
Returns an enumeration of the values in this dictionary.abstract V
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
Maps the specifiedkey
to the specifiedvalue
in this dictionary.abstract V
Removes thekey
(and its correspondingvalue
) from this dictionary.abstract int
size()
Returns the number of entries (distinct keys) in this dictionary.
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Constructor Details
-
Dictionary
public Dictionary()Sole constructor. (For invocation by subclass constructors, typically implicit.)
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-
Method Details
-
size
public abstract int size()Returns the number of entries (distinct keys) in this dictionary.- Returns:
- the number of keys in this dictionary.
-
isEmpty
public abstract boolean isEmpty()Tests if this dictionary maps no keys to value. The general contract for theisEmpty
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.
-
keys
Returns an enumeration of the keys in this dictionary. The general contract for the keys method is that anEnumeration
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:
-
elements
Returns an enumeration of the values in this dictionary. The general contract for theelements
method is that anEnumeration
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:
-
get
Returns the value to which the key is mapped in this dictionary. The general contract for theisEmpty
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 thekey
isnull
.- See Also:
-
put
Maps the specifiedkey
to the specifiedvalue
in this dictionary. Neither the key nor the value can benull
.If this dictionary already contains an entry for the specified
key
, the value already in this dictionary for thatkey
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 specifiedkey
andvalue
, andnull
is returned.The
value
can be retrieved by calling theget
method with akey
that is equal to the originalkey
.- 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 thekey
orvalue
isnull
.- See Also:
-
remove
Removes thekey
(and its correspondingvalue
) from this dictionary. This method does nothing if thekey
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
- ifkey
isnull
.
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