1 /*
2 * Copyright (c) 1995, 2004, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 /**
29 * The {@code Dictionary} class is the abstract parent of any
30 * class, such as {@code Hashtable}, which maps keys to values.
31 * Every key and every value is an object. In any one {@code Dictionary}
32 * object, every key is associated with at most one value. Given a
33 * {@code Dictionary} and a key, the associated element can be looked up.
34 * Any non-{@code null} object can be used as a key and as a value.
35 * <p>
36 * As a rule, the {@code equals} method should be used by
37 * implementations of this class to decide if two keys are the same.
38 * <p>
39 * <strong>NOTE: This class is obsolete. New implementations should
40 * implement the Map interface, rather than extending this class.</strong>
41 *
42 * @author unascribed
43 * @see java.util.Map
44 * @see java.lang.Object#equals(java.lang.Object)
45 * @see java.lang.Object#hashCode()
46 * @see java.util.Hashtable
47 * @since 1.0
48 */
49 public abstract
50 class Dictionary<K,V> {
51 /**
52 * Sole constructor. (For invocation by subclass constructors, typically
53 * implicit.)
54 */
55 public Dictionary() {
56 }
57
58 /**
59 * Returns the number of entries (distinct keys) in this dictionary.
60 *
61 * @return the number of keys in this dictionary.
62 */
63 public abstract int size();
64
65 /**
66 * Tests if this dictionary maps no keys to value. The general contract
67 * for the {@code isEmpty} method is that the result is true if and only
68 * if this dictionary contains no entries.
69 *
70 * @return {@code true} if this dictionary maps no keys to values;
71 * {@code false} otherwise.
72 */
73 public abstract boolean isEmpty();
74
75 /**
76 * Returns an enumeration of the keys in this dictionary. The general
77 * contract for the keys method is that an {@code Enumeration} object
78 * is returned that will generate all the keys for which this dictionary
79 * contains entries.
80 *
81 * @return an enumeration of the keys in this dictionary.
82 * @see java.util.Dictionary#elements()
83 * @see java.util.Enumeration
84 */
85 public abstract Enumeration<K> keys();
86
87 /**
88 * Returns an enumeration of the values in this dictionary. The general
89 * contract for the {@code elements} method is that an
90 * {@code Enumeration} is returned that will generate all the elements
91 * contained in entries in this dictionary.
92 *
93 * @return an enumeration of the values in this dictionary.
94 * @see java.util.Dictionary#keys()
95 * @see java.util.Enumeration
96 */
97 public abstract Enumeration<V> elements();
98
99 /**
100 * Returns the value to which the key is mapped in this dictionary.
101 * The general contract for the {@code isEmpty} method is that if this
102 * dictionary contains an entry for the specified key, the associated
103 * value is returned; otherwise, {@code null} 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} if the key is not mapped to any value in
108 * this dictionary.
109 * @exception NullPointerException if the {@code key} is {@code null}.
110 * @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)
111 */
112 public abstract V get(Object key);
113
114 /**
115 * Maps the specified {@code key} to the specified
116 * {@code value} in this dictionary. Neither the key nor the
117 * value can be {@code null}.
118 * <p>
119 * If this dictionary already contains an entry for the specified
120 * {@code key}, the value already in this dictionary for that
121 * {@code key} 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 {@code key}, an entry is created for the
124 * specified {@code key} and {@code value}, and {@code null} is
125 * returned.
126 * <p>
127 * The {@code value} can be retrieved by calling the
128 * {@code get} method with a {@code key} that is equal to
129 * the original {@code key}.
130 *
131 * @param key the hashtable key.
132 * @param value the value.
133 * @return the previous value to which the {@code key} was mapped
134 * in this dictionary, or {@code null} if the key did not
135 * have a previous mapping.
136 * @exception NullPointerException if the {@code key} or
137 * {@code value} is {@code null}.
138 * @see java.lang.Object#equals(java.lang.Object)
139 * @see java.util.Dictionary#get(java.lang.Object)
140 */
141 public abstract V put(K key, V value);
142
143 /**
144 * Removes the {@code key} (and its corresponding
145 * {@code value}) from this dictionary. This method does nothing
146 * if the {@code key} 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} had been mapped in this
150 * dictionary, or {@code null} if the key did not have a
151 * mapping.
152 * @exception NullPointerException if {@code key} is {@code null}.
153 */
154 public abstract V remove(Object key);
155 }