001 /*
002 * Copyright 1995-2004 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package java.util;
027
028 /**
029 * The <code>Dictionary</code> class is the abstract parent of any
030 * class, such as <code>Hashtable</code>, which maps keys to values.
031 * Every key and every value is an object. In any one <tt>Dictionary</tt>
032 * object, every key is associated with at most one value. Given a
033 * <tt>Dictionary</tt> and a key, the associated element can be looked up.
034 * Any non-<code>null</code> object can be used as a key and as a value.
035 * <p>
036 * As a rule, the <code>equals</code> method should be used by
037 * implementations of this class to decide if two keys are the same.
038 * <p>
039 * <strong>NOTE: This class is obsolete. New implementations should
040 * implement the Map interface, rather than extending this class.</strong>
041 *
042 * @author unascribed
043 * @version 1.30, 05/05/07
044 * @see java.util.Map
045 * @see java.lang.Object#equals(java.lang.Object)
046 * @see java.lang.Object#hashCode()
047 * @see java.util.Hashtable
048 * @since JDK1.0
049 */
050 public abstract class Dictionary<K, V> {
051 /**
052 * Sole constructor. (For invocation by subclass constructors, typically
053 * implicit.)
054 */
055 public Dictionary() {
056 }
057
058 /**
059 * Returns the number of entries (distinct keys) in this dictionary.
060 *
061 * @return the number of keys in this dictionary.
062 */
063 abstract public int size();
064
065 /**
066 * Tests if this dictionary maps no keys to value. The general contract
067 * for the <tt>isEmpty</tt> method is that the result is true if and only
068 * if this dictionary contains no entries.
069 *
070 * @return <code>true</code> if this dictionary maps no keys to values;
071 * <code>false</code> otherwise.
072 */
073 abstract public boolean isEmpty();
074
075 /**
076 * Returns an enumeration of the keys in this dictionary. The general
077 * contract for the keys method is that an <tt>Enumeration</tt> object
078 * is returned that will generate all the keys for which this dictionary
079 * contains entries.
080 *
081 * @return an enumeration of the keys in this dictionary.
082 * @see java.util.Dictionary#elements()
083 * @see java.util.Enumeration
084 */
085 abstract public Enumeration<K> keys();
086
087 /**
088 * Returns an enumeration of the values in this dictionary. The general
089 * contract for the <tt>elements</tt> method is that an
090 * <tt>Enumeration</tt> is returned that will generate all the elements
091 * contained in entries in this dictionary.
092 *
093 * @return an enumeration of the values in this dictionary.
094 * @see java.util.Dictionary#keys()
095 * @see java.util.Enumeration
096 */
097 abstract public Enumeration<V> elements();
098
099 /**
100 * Returns the value to which the key is mapped in this dictionary.
101 * The general contract for the <tt>isEmpty</tt> method is that if this
102 * dictionary contains an entry for the specified key, the associated
103 * value is returned; otherwise, <tt>null</tt> is returned.
104 *
105 * @return the value to which the key is mapped in this dictionary;
106 * @param key a key in this dictionary.
107 * <code>null</code> if the key is not mapped to any value in
108 * this dictionary.
109 * @exception NullPointerException if the <tt>key</tt> is <tt>null</tt>.
110 * @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)
111 */
112 abstract public V get(Object key);
113
114 /**
115 * Maps the specified <code>key</code> to the specified
116 * <code>value</code> in this dictionary. Neither the key nor the
117 * value can be <code>null</code>.
118 * <p>
119 * If this dictionary already contains an entry for the specified
120 * <tt>key</tt>, the value already in this dictionary for that
121 * <tt>key</tt> is returned, after modifying the entry to contain the
122 * new element. <p>If this dictionary does not already have an entry
123 * for the specified <tt>key</tt>, an entry is created for the
124 * specified <tt>key</tt> and <tt>value</tt>, and <tt>null</tt> is
125 * returned.
126 * <p>
127 * The <code>value</code> can be retrieved by calling the
128 * <code>get</code> method with a <code>key</code> that is equal to
129 * the original <code>key</code>.
130 *
131 * @param key the hashtable key.
132 * @param value the value.
133 * @return the previous value to which the <code>key</code> was mapped
134 * in this dictionary, or <code>null</code> if the key did not
135 * have a previous mapping.
136 * @exception NullPointerException if the <code>key</code> or
137 * <code>value</code> is <code>null</code>.
138 * @see java.lang.Object#equals(java.lang.Object)
139 * @see java.util.Dictionary#get(java.lang.Object)
140 */
141 abstract public V put(K key, V value);
142
143 /**
144 * Removes the <code>key</code> (and its corresponding
145 * <code>value</code>) from this dictionary. This method does nothing
146 * if the <code>key</code> is not in this dictionary.
147 *
148 * @param key the key that needs to be removed.
149 * @return the value to which the <code>key</code> had been mapped in this
150 * dictionary, or <code>null</code> if the key did not have a
151 * mapping.
152 * @exception NullPointerException if <tt>key</tt> is <tt>null</tt>.
153 */
154 abstract public V remove(Object key);
155 }
|