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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.util;

/**

 * The <code>Dictionary</code> class is the abstract parent of any

 * class, such as <code>Hashtable</code>, which maps keys to values.

 * Every key and every value is an object. In any one <tt>Dictionary</tt>

 * object, every key is associated with at most one value. Given a

 * <tt>Dictionary</tt> and a key, the associated element can be looked up.

 * Any non-<code>null</code> object can be used as a key and as a value.

 * <p>

 * As a rule, the <code>equals</code> 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NOTE: This class is obsolete.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   JDK1.0

 */

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.

     */

    abstract public int size();

    /**

     * Tests if this dictionary maps no keys to value. The general contract

     * for the <tt>isEmpty</tt> method is that the result is true if and only

     * if this dictionary contains no entries.

     *

     * @return  <code>true</code> if this dictionary maps no keys to values;

     *          <code>false</code> otherwise.

     */

    abstract public boolean isEmpty();

    /**

     * Returns an enumeration of the keys in this dictionary. The general

     * contract for the keys method is that an <tt>Enumeration</tt> 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

     */

    abstract public Enumeration<K> keys();

    /**

     * Returns an enumeration of the values in this dictionary. The general

     * contract for the <tt>elements</tt> method is that an

     * <tt>Enumeration</tt> 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

     */

    abstract public Enumeration<V> elements();

    /**

     * Returns the value to which the key is mapped in this dictionary.

     * The general contract for the <tt>isEmpty</tt> method is that if this

     * dictionary contains an entry for the specified key, the associated

     * value is returned; otherwise, <tt>null</tt> is returned.

     *

     * @return  the value to which the key is mapped in this dictionary;

     * @param   key   a key in this dictionary.

     *          <code>null</code> if the key is not mapped to any value in

     *          this dictionary.

     * @exception NullPointerException if the <tt>key</tt> is <tt>null</tt>.

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

     */

    abstract public V get(Object key);

    /**

     * Maps the specified <code>key</code> to the specified

     * <code>value</code> in this dictionary. Neither the key nor the

     * value can be <code>null</code>.

     * <p>

     * If this dictionary already contains an entry for the specified

     * <tt>key</tt>, the value already in this dictionary for that

     * <tt>key</tt> is returned, after modifying the entry to contain the

     *  new element. <p>If this dictionary does not already have an entry

     *  for the specified <tt>key</tt>, an entry is created for the

     *  specified <tt>key</tt> and <tt>value</tt>, and <tt>null</tt> is

     *  returned.

     * <p>

     * The <code>value</code> can be retrieved by calling the

     * <code>get</code> method with a <code>key</code> that is equal to

     * the original <code>key</code>.

     *

     * @param      key     the hashtable key.

     * @param      value   the value.

     * @return     the previous value to which the <code>key</code> was mapped

     *             in this dictionary, or <code>null</code> if the key did not

     *             have a previous mapping.

     * @exception  NullPointerException  if the <code>key</code> or

     *               <code>value</code> is <code>null</code>.

     * @see        java.lang.Object#equals(java.lang.Object)

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

     */

    abstract public V put(K key, V value);

    /**

     * Removes the <code>key</code> (and its corresponding

     * <code>value</code>) from this dictionary. This method does nothing

     * if the <code>key</code> is not in this dictionary.

     *

     * @param   key   the key that needs to be removed.

     * @return  the value to which the <code>key</code> had been mapped in this

     *          dictionary, or <code>null</code> if the key did not have a

     *          mapping.

     * @exception NullPointerException if <tt>key</tt> is <tt>null</tt>.

     */

    abstract public V remove(Object key);

}