Class java.util.Dictionary - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.util.Dictionary

java.lang.Object
   |
   +----java.util.Dictionary

public abstract class Dictionary
extends Object

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

See Also:: equals, hashCode, Hashtable

Dictionary()

elements(): Returns an enumeration of the values in this dictionary.
get(Object): Returns the value to which the key is mapped in this dictionary.
isEmpty(): Tests if this dictionary maps no keys to value.
keys(): Returns an enumeration of the keys in this dictionary.
put(Object, Object): Maps the specified key to the specified value in this dictionary.
remove(Object): Removes the key (and its corresponding value) from this dictionary.
size(): Returns the number of keys in this dictionary.

Dictionary

 public Dictionary()

size

 public abstract int size()

Returns the number of 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.

Returns:: true if this dictionary maps no keys to values; false otherwise.

keys

 public abstract Enumeration keys()

Returns an enumeration of the keys in this dictionary.

Returns:: an enumeration of the keys in this dictionary.
See Also:: elements, Enumeration

elements

 public abstract Enumeration elements()

Returns an enumeration of the values in this dictionary. the Enumeration methods on the returned object to fetch the elements sequentially.

Returns:: an enumeration of the values in this dictionary.
See Also:: keys, Enumeration

get

 public abstract Object get(Object key)

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.
Returns:: the value to which the key is mapped in this dictionary;
See Also:: put

put

 public abstract Object put(Object key,
                            Object value)

Maps the specified key to the specified value in this dictionary. Neither the key nor the value can be null.

The value can be retrieved by calling the get method with a key that is equal to the original key.

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

remove

 public abstract Object 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.

Parameters:: key - the key that needs to be removed.
Returns:: the value to which the key had been mapped in this dictionary, or null if the key did not have a mapping.

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