Dictionary.java revision 51b1b6997fd3f980076b8081f7f1165ccc2a4008 
1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
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14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
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25
26package java.util;
27
28/**
29 * The <code>Dictionary</code> class is the abstract parent of any
30 * class, such as <code>Hashtable</code>, which maps keys to values.
31 * Every key and every value is an object. In any one <tt>Dictionary</tt>
32 * object, every key is associated with at most one value. Given a
33 * <tt>Dictionary</tt> and a key, the associated element can be looked up.
34 * Any non-<code>null</code> object can be used as a key and as a value.
35 * <p>
36 * As a rule, the <code>equals</code> 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NOTE: This class is obsolete.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   JDK1.0
48 */
49public abstract
50class 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    abstract public int size();
64
65    /**
66     * Tests if this dictionary maps no keys to value. The general contract
67     * for the <tt>isEmpty</tt> method is that the result is true if and only
68     * if this dictionary contains no entries.
69     *
70     * @return  <code>true</code> if this dictionary maps no keys to values;
71     *          <code>false</code> otherwise.
72     */
73    abstract public 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 <tt>Enumeration</tt> 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    abstract public Enumeration<K> keys();
86
87    /**
88     * Returns an enumeration of the values in this dictionary. The general
89     * contract for the <tt>elements</tt> method is that an
90     * <tt>Enumeration</tt> 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    abstract public Enumeration<V> elements();
98
99    /**
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}
156