/* * Copyright (c) 1995, 2004, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * 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 * or visit www.oracle.com if you need additional information or have any * questions. */ 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NOTE: This class is obsolete.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 abstractclass 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);}