1 /* 2 * Copyright (c) 1995, 2020, 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NOTE: This class is obsolete.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 * @see java.util.Map 43 * @see java.lang.Object#equals(java.lang.Object) 44 * @see java.lang.Object#hashCode() 45 * @see java.util.Hashtable 46 * @since 1.0 47 */ 48 public abstract 49 class Dictionary<K,V> { 50 /** 51 * Sole constructor. (For invocation by subclass constructors, typically 52 * implicit.) 53 */ Dictionary()54 public Dictionary() { 55 } 56 57 /** 58 * Returns the number of entries (distinct keys) in this dictionary. 59 * 60 * @return the number of keys in this dictionary. 61 */ size()62 public abstract int size(); 63 64 /** 65 * Tests if this dictionary maps no keys to value. The general contract 66 * for the {@code isEmpty} method is that the result is true if and only 67 * if this dictionary contains no entries. 68 * 69 * @return {@code true} if this dictionary maps no keys to values; 70 * {@code false} otherwise. 71 */ isEmpty()72 public abstract boolean isEmpty(); 73 74 /** 75 * Returns an enumeration of the keys in this dictionary. The general 76 * contract for the keys method is that an {@code Enumeration} object 77 * is returned that will generate all the keys for which this dictionary 78 * contains entries. 79 * 80 * @return an enumeration of the keys in this dictionary. 81 * @see java.util.Dictionary#elements() 82 * @see java.util.Enumeration 83 */ keys()84 public abstract Enumeration<K> keys(); 85 86 /** 87 * Returns an enumeration of the values in this dictionary. The general 88 * contract for the {@code elements} method is that an 89 * {@code Enumeration} is returned that will generate all the elements 90 * contained in entries in this dictionary. 91 * 92 * @return an enumeration of the values in this dictionary. 93 * @see java.util.Dictionary#keys() 94 * @see java.util.Enumeration 95 */ elements()96 public abstract Enumeration<V> elements(); 97 98 /** 99 * Returns the value to which the key is mapped in this dictionary. 100 * The general contract for the {@code isEmpty} method is that if this 101 * dictionary contains an entry for the specified key, the associated 102 * value is returned; otherwise, {@code null} is returned. 103 * 104 * @return the value to which the key is mapped in this dictionary; 105 * @param key a key in this dictionary. 106 * {@code null} if the key is not mapped to any value in 107 * this dictionary. 108 * @throws NullPointerException if the {@code key} is {@code null}. 109 * @see java.util.Dictionary#put(java.lang.Object, java.lang.Object) 110 */ get(Object key)111 public abstract V get(Object key); 112 113 /** 114 * Maps the specified {@code key} to the specified 115 * {@code value} in this dictionary. Neither the key nor the 116 * value can be {@code null}. 117 * <p> 118 * If this dictionary already contains an entry for the specified 119 * {@code key}, the value already in this dictionary for that 120 * {@code key} is returned, after modifying the entry to contain the 121 * new element. <p>If this dictionary does not already have an entry 122 * for the specified {@code key}, an entry is created for the 123 * specified {@code key} and {@code value}, and {@code null} is 124 * returned. 125 * <p> 126 * The {@code value} can be retrieved by calling the 127 * {@code get} method with a {@code key} that is equal to 128 * the original {@code key}. 129 * 130 * @param key the hashtable key. 131 * @param value the value. 132 * @return the previous value to which the {@code key} was mapped 133 * in this dictionary, or {@code null} if the key did not 134 * have a previous mapping. 135 * @throws NullPointerException if the {@code key} or 136 * {@code value} is {@code null}. 137 * @see java.lang.Object#equals(java.lang.Object) 138 * @see java.util.Dictionary#get(java.lang.Object) 139 */ put(K key, V value)140 public abstract V put(K key, V value); 141 142 /** 143 * Removes the {@code key} (and its corresponding 144 * {@code value}) from this dictionary. This method does nothing 145 * if the {@code key} is not in this dictionary. 146 * 147 * @param key the key that needs to be removed. 148 * @return the value to which the {@code key} had been mapped in this 149 * dictionary, or {@code null} if the key did not have a 150 * mapping. 151 * @throws NullPointerException if {@code key} is {@code null}. 152 */ remove(Object key)153 public abstract V remove(Object key); 154 } 155