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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * accompanied this code).

 *

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package java.util;

/**

 * 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NOTE: This class is obsolete.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.)

     */

    public 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 {@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 {@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 {@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 {@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.

     * @see     java.util.Dictionary#put(java.lang.Object, java.lang.Object)

     */

    public abstract V get(Object key);

    /**

     * 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.

     *               {@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 {@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.

     */

    public abstract V remove(Object key);

}