Class: java.util.Dictionary<K, V>

  • public abstract class Dictionary<K, V>
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NOTE: This class is obsolete.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.

Authors:
@author unascribed
See:
@see java.util.Map
@see Object.equals(java.lang.Object)
@see Object.hashCode()
@see java.util.Hashtable
Version:
@version 1.23, 01/12/04
Since:
@since JDK1.0

Inheritance

Superclass tree:

Methods

  • Dictionarytop

    public Dictionary()
    Sole constructor. (For invocation by subclass constructors, typically implicit.)
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  • elementstop

    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.
    Return:
    @return an enumeration of the values in this dictionary.
    See:
    @see java.util.Dictionary.keys()
    @see java.util.Enumeration
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  • gettop

    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.
    Parameters:
    @param key a key in this dictionary. null if the key is not mapped to any value in this dictionary.
    Return:
    @return the value to which the key is mapped in this dictionary;
    Exceptions:
    @exception NullPointerException if the key is null.
    See:
    @see java.util.Dictionary.put(java.lang.Object, java.lang.Object)
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  • isEmptytop

    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.
    Return:
    @return true if this dictionary maps no keys to values; false otherwise.
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  • keystop

    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.
    Return:
    @return an enumeration of the keys in this dictionary.
    See:
    @see java.util.Dictionary.elements()
    @see java.util.Enumeration
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  • puttop

    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.

    Parameters:
    @param key the hashtable key.
    @param value the value.
    Return:
    @return the previous value to which the key was mapped in this dictionary, or null if the key did not have a previous mapping.
    Exceptions:
    @exception NullPointerException if the key or value is null.
    See:
    @see Object.equals(java.lang.Object)
    @see java.util.Dictionary.get(java.lang.Object)
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  • removetop

    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.
    Parameters:
    @param key the key that needs to be removed.
    Return:
    @return the value to which the key had been mapped in this dictionary, or null if the key did not have a mapping.
    Exceptions:
    @exception NullPointerException if key is null.
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  • sizetop

    public abstract int size()
    Returns the number of entries (distinct keys) in this dictionary.
    Return:
    @return the number of keys in this dictionary.
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