Dictionary JDK 1.6)

Description

publicabstract abstract class Dictionary

The Dictionary class is the abstract parent of any class, such as Hashtable, which maps keys to values.

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NOTE: This class is obsolete.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.

See also: Map Object.equals(java.lang.Object) Object.hashCode() Hashtable

Methods

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publicabstract Enumeration< V> elements ()

Returns an enumeration of the values in this dictionary.

publicabstract V get (Object key)

Returns the value to which the key is mapped in this dictionary.

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.
Returns: the value to which the key is mapped in this dictionary;
Parameters:
- key - a key in this dictionary. null if the key is not mapped to any value in this dictionary.
Throws:
- NullPointerException - if the key is null.
See Also: Dictionary.put(java.lang.Object, java.lang.Object),

publicabstract boolean isEmpty ()

Tests if this dictionary maps no keys to value.

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.

publicabstract Enumeration< K> keys ()

Returns an enumeration of the keys in this dictionary.

publicabstract V put ( K key, V value)

Maps the specified key to the specified value in this dictionary.

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.
Returns: the previous value to which the key was mapped in this dictionary, or null if the key did not have a previous mapping.
Parameters:
- key - the hashtable key.
- value - the value.
Throws:
- NullPointerException - if the key or value is null.
See Also: Object.equals(java.lang.Object), Dictionary.get(java.lang.Object),

publicabstract V remove (Object key)

Removes the key (and its corresponding value) from this dictionary.

Removes the key (and its corresponding
value) from this dictionary. This method does nothing
if the key is not in this dictionary.
Returns: the value to which the key had been mapped in this dictionary, or null if the key did not have a mapping.
Parameters:
- key - the key that needs to be removed.
Throws:
- NullPointerException - if key is null.

publicabstract int size ()

Returns the number of entries (distinct keys) in this dictionary.