| Dictionary.java |
1 /*
2 * %W% %E%
3 *
4 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
5 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6 */
7
8 package java.util;
9
10 /**
11 * The <code>Dictionary</code> class is the abstract parent of any
12 * class, such as <code>Hashtable</code>, which maps keys to values.
13 * Every key and every value is an object. In any one <tt>Dictionary</tt>
14 * object, every key is associated with at most one value. Given a
15 * <tt>Dictionary</tt> and a key, the associated element can be looked up.
16 * Any non-<code>null</code> object can be used as a key and as a value.
17 * <p>
18 * As a rule, the <code>equals</code> method should be used by
19 * implementations of this class to decide if two keys are the same.
20 * <p>
21 * <strong>NOTE: This class is obsolete. New implementations should
22 * implement the Map interface, rather than extending this class.</strong>
23 *
24 * @author unascribed
25 * @version %I%, %G%
26 * @see java.util.Map
27 * @see java.lang.Object#equals(java.lang.Object)
28 * @see java.lang.Object#hashCode()
29 * @see java.util.Hashtable
30 * @since JDK1.0
31 */
32 public abstract
33 class Dictionary<K,V> {
34 /**
35 * Sole constructor. (For invocation by subclass constructors, typically
36 * implicit.)
37 */
38 public Dictionary() {
39 }
40
41 /**
42 * Returns the number of entries (distinct keys) in this dictionary.
43 *
44 * @return the number of keys in this dictionary.
45 */
46 abstract public int size();
47
48 /**
49 * Tests if this dictionary maps no keys to value. The general contract
50 * for the <tt>isEmpty</tt> method is that the result is true if and only
51 * if this dictionary contains no entries.
52 *
53 * @return <code>true</code> if this dictionary maps no keys to values;
54 * <code>false</code> otherwise.
55 */
56 abstract public boolean isEmpty();
57
58 /**
59 * Returns an enumeration of the keys in this dictionary. The general
60 * contract for the keys method is that an <tt>Enumeration</tt> object
61 * is returned that will generate all the keys for which this dictionary
62 * contains entries.
63 *
64 * @return an enumeration of the keys in this dictionary.
65 * @see java.util.Dictionary#elements()
66 * @see java.util.Enumeration
67 */
68 abstract public Enumeration<K> keys();
69
70 /**
71 * Returns an enumeration of the values in this dictionary. The general
72 * contract for the <tt>elements</tt> method is that an
73 * <tt>Enumeration</tt> is returned that will generate all the elements
74 * contained in entries in this dictionary.
75 *
76 * @return an enumeration of the values in this dictionary.
77 * @see java.util.Dictionary#keys()
78 * @see java.util.Enumeration
79 */
80 abstract public Enumeration<V> elements();
81
82 /**
83 * Returns the value to which the key is mapped in this dictionary.
84 * The general contract for the <tt>isEmpty</tt> method is that if this
85 * dictionary contains an entry for the specified key, the associated
86 * value is returned; otherwise, <tt>null</tt> is returned.
87 *
88 * @return the value to which the key is mapped in this dictionary;
89 * @param key a key in this dictionary.
90 * <code>null</code> if the key is not mapped to any value in
91 * this dictionary.
92 * @exception NullPointerException if the <tt>key</tt> is <tt>null</tt>.
93 * @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)
94 */
95 abstract public V get(Object key);
96
97 /**
98 * Maps the specified <code>key</code> to the specified
99 * <code>value</code> in this dictionary. Neither the key nor the
100 * value can be <code>null</code>.
101 * <p>
102 * If this dictionary already contains an entry for the specified
103 * <tt>key</tt>, the value already in this dictionary for that
104 * <tt>key</tt> is returned, after modifying the entry to contain the
105 * new element. <p>If this dictionary does not already have an entry
106 * for the specified <tt>key</tt>, an entry is created for the
107 * specified <tt>key</tt> and <tt>value</tt>, and <tt>null</tt> is
108 * returned.
109 * <p>
110 * The <code>value</code> can be retrieved by calling the
111 * <code>get</code> method with a <code>key</code> that is equal to
112 * the original <code>key</code>.
113 *
114 * @param key the hashtable key.
115 * @param value the value.
116 * @return the previous value to which the <code>key</code> was mapped
117 * in this dictionary, or <code>null</code> if the key did not
118 * have a previous mapping.
119 * @exception NullPointerException if the <code>key</code> or
120 * <code>value</code> is <code>null</code>.
121 * @see java.lang.Object#equals(java.lang.Object)
122 * @see java.util.Dictionary#get(java.lang.Object)
123 */
124 abstract public V put(K key, V value);
125
126 /**
127 * Removes the <code>key</code> (and its corresponding
128 * <code>value</code>) from this dictionary. This method does nothing
129 * if the <code>key</code> is not in this dictionary.
130 *
131 * @param key the key that needs to be removed.
132 * @return the value to which the <code>key</code> had been mapped in this
133 * dictionary, or <code>null</code> if the key did not have a
134 * mapping.
135 * @exception NullPointerException if <tt>key</tt> is <tt>null</tt>.
136 */
137 abstract public V remove(Object key);
138 }
139