Dictionary (Java Platform SE 8 ) (original) (raw)

• java.lang.Object

• • java.util.Dictionary<K,V>

• Direct Known Subclasses:
  Hashtable

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NOTE: This class is obsolete.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.
Since:
JDK1.0
See Also:
Map, Object.equals(java.lang.Object), Object.hashCode(), Hashtable

• • Constructor Summary

  Constructors

  Constructor	Description
  Dictionary()	Sole constructor.

  • Method Summary

  All Methods Instance Methods Abstract Methods

  Modifier and Type	Method	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 specified key to the specifiedvalue in this dictionary.
  abstract V	remove(Object key)	Removes the key (and its correspondingvalue) from this dictionary.
  abstract int	size()	Returns the number of entries (distinct keys) in this dictionary.

     * ### Methods inherited from class java.lang.[Object](../../java/lang/Object.html "class in java.lang")  
     `[clone](../../java/lang/Object.html#clone--), [equals](../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../java/lang/Object.html#finalize--), [getClass](../../java/lang/Object.html#getClass--), [hashCode](../../java/lang/Object.html#hashCode--), [notify](../../java/lang/Object.html#notify--), [notifyAll](../../java/lang/Object.html#notifyAll--), [toString](../../java/lang/Object.html#toString--), [wait](../../java/lang/Object.html#wait--), [wait](../../java/lang/Object.html#wait-long-), [wait](../../java/lang/Object.html#wait-long-int-)`

• • 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](../../java/util/Enumeration.html "interface in java.util")<[K](../../java/util/Dictionary.html "type parameter in Dictionary")> 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()](../../java/util/Dictionary.html#elements--), [Enumeration](../../java/util/Enumeration.html "interface in java.util")  
    * #### elements  
    public abstract [Enumeration](../../java/util/Enumeration.html "interface in java.util")<[V](../../java/util/Dictionary.html "type parameter in Dictionary")> 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()](../../java/util/Dictionary.html#keys--), [Enumeration](../../java/util/Enumeration.html "interface in java.util")  
    * #### get  
    public abstract [V](../../java/util/Dictionary.html "type parameter in Dictionary") get([Object](../../java/lang/Object.html "class in java.lang") 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](../../java/lang/NullPointerException.html "class in java.lang")` \- if the key is null.  
    See Also:  
    [put(java.lang.Object, java.lang.Object)](../../java/util/Dictionary.html#put-K-V-)  
    * #### put  
    public abstract [V](../../java/util/Dictionary.html "type parameter in Dictionary") put([K](../../java/util/Dictionary.html "type parameter in Dictionary") key,  
                          [V](../../java/util/Dictionary.html "type parameter in Dictionary") 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 specifiedkey, the value already in this dictionary for thatkey 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`.  
    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](../../java/lang/NullPointerException.html "class in java.lang")` \- if the `key` or`value` is `null`.  
    See Also:  
    [Object.equals(java.lang.Object)](../../java/lang/Object.html#equals-java.lang.Object-), [get(java.lang.Object)](../../java/util/Dictionary.html#get-java.lang.Object-)  
    * #### remove  
    public abstract [V](../../java/util/Dictionary.html "type parameter in Dictionary") remove([Object](../../java/lang/Object.html "class in java.lang") 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.  
    Throws:  
    `[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if key is null.

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