- java.lang.Object
-
- java.util.Dictionary<K,V>
-
- Direct Known Subclasses:
- Hashtable
public abstract class Dictionary<K,V> extends Object
TheDictionary
class is the abstract parent of any class, such asHashtable
, 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method should be used by implementations of this class to decide if two keys are the same.NOTE: This class is obsolete.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:
- JDK1.0
- See Also:
Map
,Object.equals(java.lang.Object)
,Object.hashCode()
,Hashtable
-
-
Constructor Summary
Constructors Constructor and Description Dictionary()
Sole constructor.
-
Method Summary
Methods Modifier and Type Method and Description 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 specifiedkey
to the specifiedvalue
in this dictionary.abstract V
remove(Object key)
Removes thekey
(and its correspondingvalue
) from this dictionary.abstract int
size()
Returns the number of entries (distinct keys) in this dictionary.
-
-
-
Constructor Detail
-
Dictionary
public Dictionary()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
-
-
Method Detail
-
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 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.
-
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:
- an enumeration of the keys in this dictionary.
- See Also:
elements()
,Enumeration
-
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:
- an enumeration of the values in this dictionary.
- See Also:
keys()
,Enumeration
-
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
- 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.- See Also:
put(java.lang.Object, java.lang.Object)
-
put
public abstract V put(K key, V value)
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 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 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:
Object.equals(java.lang.Object)
,get(java.lang.Object)
-
remove
public abstract V remove(Object key)
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
- if key is null.
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