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</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NOTE: This class is obsolete.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 */ 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 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
