java.util

Class Dictionary<K,V>

java.lang.Object

java.util.Dictionary<K,V>

Direct Known Subclasses:

Hashtable

public abstract class Dictionary<K,V>
extends Object

A Dictionary maps keys to values; how it does that is implementation-specific. This is an abstract class which has really gone by the wayside. People at Javasoft are probably embarrassed by it. At this point, it might as well be an interface rather than a class, but it remains this poor, laughable skeleton for the sake of backwards compatibility. At any rate, this was what came before the Map interface in the Collections framework.

Since:

1.0

Author:

Jon Zeppieri, Eric Blake (ebb9@email.byu.edu)

See Also:

Map, Hashtable

Constructor Summary

Constructors

Constructor and Description
Dictionary() Sole constructor (often called implicitly).

Method Summary

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 associated with the supplied key, or null if no such value exists.
abstract boolean	isEmpty() Returns true when there are no elements in this Dictionary.
abstract Enumeration<K>	keys() Returns an Enumeration of the keys in this Dictionary
abstract V	put(K key, V value) Inserts a new value into this Dictionary, located by the supplied key.
abstract V	remove(Object key) Removes from the Dictionary the value located by the given key.
abstract int	size() Returns the number of values currently in this Dictionary.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Dictionary

public Dictionary()

Sole constructor (often called implicitly).

Method Detail

elements

public abstract Enumeration<V> elements()

Returns an Enumeration of the values in this Dictionary.

Returns:

an Enumeration of the values

See Also:

keys()

get

public abstract V get(Object key)

Returns the value associated with the supplied key, or null if no such value exists. Since Dictionaries are not allowed null keys or elements, a null result always means the key is not present.

Parameters:

key - the key to use to fetch the value

Returns:

the mapped value

Throws:

NullPointerException - if key is null

See Also:

put(Object, Object)

isEmpty

public abstract boolean isEmpty()

Returns true when there are no elements in this Dictionary.

Returns:

size() == 0

keys

public abstract Enumeration<K> keys()

Returns an Enumeration of the keys in this Dictionary

Returns:

an Enumeration of the keys

See Also:

elements()

put

public abstract V put(K key,
                      V value)

Inserts a new value into this Dictionary, located by the supplied key. Dictionary does not support null keys or values, so a null return can safely be interpreted as adding a new key.

Parameters:

key - the key which locates the value

value - the value to put into the Dictionary

Returns:

the previous value of the key, or null if there was none

Throws:

NullPointerException - if key or value is null

See Also:

get(Object)

remove

public abstract V remove(Object key)

Removes from the Dictionary the value located by the given key. A null return safely means that the key was not mapped in the Dictionary.

Parameters:

key - the key used to locate the value to be removed

Returns:

the value associated with the removed key

Throws:

NullPointerException - if key is null

size

public abstract int size()

Returns the number of values currently in this Dictionary.

Returns:

the number of keys in the Dictionary