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package java.util;


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NOTE: This class is obsolete.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.

Author: unascribed
See Also:
Since:  1.0
/**
 * The {@code Dictionary} class is the abstract parent of any
 * class, such as {@code Hashtable}, which maps keys to values.
 * Every key and every value is an object. In any one {@code Dictionary}
 * object, every key is associated with at most one value. Given a
 * {@code Dictionary} and a key, the associated element can be looked up.
 * Any non-{@code null} object can be used as a key and as a value.
 * <p>
 * As a rule, the {@code equals} method should be used by
 * implementations of this class to decide if two keys are the same.
 * <p>
 * <strong>NOTE: This class is obsolete.  New implementations should
 * implement the Map interface, rather than extending this class.</strong>
 *
 * @author  unascribed
 * @see     java.util.Map
 * @see     java.lang.Object#equals(java.lang.Object)
 * @see     java.lang.Object#hashCode()
 * @see     java.util.Hashtable
 * @since   1.0
 */
public abstract
class Dictionary<K,V> {
    
Sole constructor.  (For invocation by subclass constructors, typically
implicit.)

/**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    public Dictionary() {
    }

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

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

    
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.
/**
     * Tests if this dictionary maps no keys to value. The general contract
     * for the {@code isEmpty} method is that the result is true if and only
     * if this dictionary contains no entries.
     *
     * @return  {@code true} if this dictionary maps no keys to values;
     *          {@code false} otherwise.
     */
    public abstract boolean isEmpty();

    
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. 
See Also:
Returns: an enumeration of the keys in this dictionary.
/**
     * Returns an enumeration of the keys in this dictionary. The general
     * contract for the keys method is that an {@code Enumeration} object
     * is returned that will generate all the keys for which this dictionary
     * contains entries.
     *
     * @return  an enumeration of the keys in this dictionary.
     * @see     java.util.Dictionary#elements()
     * @see     java.util.Enumeration
     */
    public abstract Enumeration<K> keys();

    
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. 
See Also:
Returns: an enumeration of the values in this dictionary.
/**
     * Returns an enumeration of the values in this dictionary. The general
     * contract for the {@code elements} method is that an
     * {@code Enumeration} is returned that will generate all the elements
     * contained in entries in this dictionary.
     *
     * @return  an enumeration of the values in this dictionary.
     * @see     java.util.Dictionary#keys()
     * @see     java.util.Enumeration
     */
    public abstract Enumeration<V> elements();

    
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. 
Params:
  • key –  a key in this dictionary. null if the key is not mapped to any value in this dictionary.
Throws:
See Also:
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 {@code isEmpty} method is that if this
     * dictionary contains an entry for the specified key, the associated
     * value is returned; otherwise, {@code null} is returned.
     *
     * @return  the value to which the key is mapped in this dictionary;
     * @param   key   a key in this dictionary.
     *          {@code null} if the key is not mapped to any value in
     *          this dictionary.
     * @exception NullPointerException if the {@code key} is {@code null}.
     * @see     java.util.Dictionary#put(java.lang.Object, java.lang.Object)
     */
    public abstract V get(Object key);

    
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. 
Params:
  • key –     the hashtable key.
  • value –   the value.
Throws:
See Also:
Returns: the previous value to which the key was mapped in this dictionary, or null if the key did not have a previous mapping.
/**
     * Maps the specified {@code key} to the specified
     * {@code value} in this dictionary. Neither the key nor the
     * value can be {@code null}.
     * <p>
     * If this dictionary already contains an entry for the specified
     * {@code key}, the value already in this dictionary for that
     * {@code key} is returned, after modifying the entry to contain the
     *  new element. <p>If this dictionary does not already have an entry
     *  for the specified {@code key}, an entry is created for the
     *  specified {@code key} and {@code value}, and {@code null} is
     *  returned.
     * <p>
     * The {@code value} can be retrieved by calling the
     * {@code get} method with a {@code key} that is equal to
     * the original {@code key}.
     *
     * @param      key     the hashtable key.
     * @param      value   the value.
     * @return     the previous value to which the {@code key} was mapped
     *             in this dictionary, or {@code null} if the key did not
     *             have a previous mapping.
     * @exception  NullPointerException  if the {@code key} or
     *               {@code value} is {@code null}.
     * @see        java.lang.Object#equals(java.lang.Object)
     * @see        java.util.Dictionary#get(java.lang.Object)
     */
    public abstract V put(K key, V value);

    
Removes the key (and its corresponding value) from this dictionary. This method does nothing if the key is not in this dictionary. 
Params:
  • key –   the key that needs to be removed.
Throws:
Returns: the value to which the key had been mapped in this dictionary, or null if the key did not have a mapping.
/**
     * Removes the {@code key} (and its corresponding
     * {@code value}) from this dictionary. This method does nothing
     * if the {@code key} is not in this dictionary.
     *
     * @param   key   the key that needs to be removed.
     * @return  the value to which the {@code key} had been mapped in this
     *          dictionary, or {@code null} if the key did not have a
     *          mapping.
     * @exception NullPointerException if {@code key} is {@code null}.
     */
    public abstract V remove(Object key);
}