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NOTE: This class is obsolete.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: }
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