public abstract class Dictionary<K,V> extends Object
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NOTE: This class is obsolete.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.
Map
, Object.equals(java.lang.Object)
, Object.hashCode()
, Hashtable
public Dictionary()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
public abstract int size()
Returns the number of entries (distinct keys) in this dictionary.
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.
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.
elements()
, Enumeration
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.
keys()
, Enumeration
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.
key
- a key in this dictionary. null
if the key is not mapped to any value in this dictionary.NullPointerException
- if the key
is null
.put(java.lang.Object, java.lang.Object)
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
.
key
- the hashtable key.value
- the value.key
was mapped in this dictionary, or null
if the key did not have a previous mapping.NullPointerException
- if the key
or value
is null
.Object.equals(java.lang.Object)
, get(java.lang.Object)
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.
key
- the key that needs to be removed.key
had been mapped in this dictionary, or null
if the key did not have a mapping.NullPointerException
- if key
is null
.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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