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1 /* |
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2 * Copyright (c) 1995, 2004, Oracle and/or its affiliates. All rights reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Oracle designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Oracle in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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22 * or visit www.oracle.com if you need additional information or have any |
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23 * questions. |
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24 */ |
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25 |
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26 package java.util; |
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27 |
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28 /** |
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29 * The <code>Dictionary</code> class is the abstract parent of any |
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30 * class, such as <code>Hashtable</code>, which maps keys to values. |
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31 * Every key and every value is an object. In any one <tt>Dictionary</tt> |
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32 * object, every key is associated with at most one value. Given a |
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33 * <tt>Dictionary</tt> and a key, the associated element can be looked up. |
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34 * Any non-<code>null</code> object can be used as a key and as a value. |
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35 * <p> |
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36 * As a rule, the <code>equals</code> method should be used by |
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37 * implementations of this class to decide if two keys are the same. |
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38 * <p> |
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39 * <strong>NOTE: This class is obsolete. New implementations should |
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40 * implement the Map interface, rather than extending this class.</strong> |
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41 * |
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42 * @author unascribed |
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43 * @see java.util.Map |
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44 * @see java.lang.Object#equals(java.lang.Object) |
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45 * @see java.lang.Object#hashCode() |
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46 * @see java.util.Hashtable |
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47 * @since 1.0 |
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48 */ |
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49 public abstract |
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50 class Dictionary<K,V> { |
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51 /** |
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52 * Sole constructor. (For invocation by subclass constructors, typically |
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53 * implicit.) |
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54 */ |
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55 public Dictionary() { |
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56 } |
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57 |
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58 /** |
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59 * Returns the number of entries (distinct keys) in this dictionary. |
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60 * |
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61 * @return the number of keys in this dictionary. |
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62 */ |
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63 abstract public int size(); |
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64 |
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65 /** |
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66 * Tests if this dictionary maps no keys to value. The general contract |
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67 * for the <tt>isEmpty</tt> method is that the result is true if and only |
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68 * if this dictionary contains no entries. |
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69 * |
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70 * @return <code>true</code> if this dictionary maps no keys to values; |
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71 * <code>false</code> otherwise. |
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72 */ |
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73 abstract public boolean isEmpty(); |
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74 |
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75 /** |
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76 * Returns an enumeration of the keys in this dictionary. The general |
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77 * contract for the keys method is that an <tt>Enumeration</tt> object |
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78 * is returned that will generate all the keys for which this dictionary |
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79 * contains entries. |
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80 * |
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81 * @return an enumeration of the keys in this dictionary. |
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82 * @see java.util.Dictionary#elements() |
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83 * @see java.util.Enumeration |
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84 */ |
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85 abstract public Enumeration<K> keys(); |
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86 |
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87 /** |
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88 * Returns an enumeration of the values in this dictionary. The general |
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89 * contract for the <tt>elements</tt> method is that an |
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90 * <tt>Enumeration</tt> is returned that will generate all the elements |
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91 * contained in entries in this dictionary. |
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92 * |
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93 * @return an enumeration of the values in this dictionary. |
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94 * @see java.util.Dictionary#keys() |
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95 * @see java.util.Enumeration |
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96 */ |
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97 abstract public Enumeration<V> elements(); |
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98 |
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99 /** |
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100 * Returns the value to which the key is mapped in this dictionary. |
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101 * The general contract for the <tt>isEmpty</tt> method is that if this |
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102 * dictionary contains an entry for the specified key, the associated |
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103 * value is returned; otherwise, <tt>null</tt> is returned. |
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104 * |
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105 * @return the value to which the key is mapped in this dictionary; |
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106 * @param key a key in this dictionary. |
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107 * <code>null</code> if the key is not mapped to any value in |
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108 * this dictionary. |
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109 * @exception NullPointerException if the <tt>key</tt> is <tt>null</tt>. |
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110 * @see java.util.Dictionary#put(java.lang.Object, java.lang.Object) |
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111 */ |
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112 abstract public V get(Object key); |
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113 |
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114 /** |
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115 * Maps the specified <code>key</code> to the specified |
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116 * <code>value</code> in this dictionary. Neither the key nor the |
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117 * value can be <code>null</code>. |
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118 * <p> |
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119 * If this dictionary already contains an entry for the specified |
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120 * <tt>key</tt>, the value already in this dictionary for that |
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121 * <tt>key</tt> is returned, after modifying the entry to contain the |
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122 * new element. <p>If this dictionary does not already have an entry |
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123 * for the specified <tt>key</tt>, an entry is created for the |
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124 * specified <tt>key</tt> and <tt>value</tt>, and <tt>null</tt> is |
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125 * returned. |
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126 * <p> |
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127 * The <code>value</code> can be retrieved by calling the |
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128 * <code>get</code> method with a <code>key</code> that is equal to |
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129 * the original <code>key</code>. |
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130 * |
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131 * @param key the hashtable key. |
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132 * @param value the value. |
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133 * @return the previous value to which the <code>key</code> was mapped |
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134 * in this dictionary, or <code>null</code> if the key did not |
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135 * have a previous mapping. |
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136 * @exception NullPointerException if the <code>key</code> or |
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137 * <code>value</code> is <code>null</code>. |
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138 * @see java.lang.Object#equals(java.lang.Object) |
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139 * @see java.util.Dictionary#get(java.lang.Object) |
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140 */ |
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141 abstract public V put(K key, V value); |
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142 |
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143 /** |
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144 * Removes the <code>key</code> (and its corresponding |
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145 * <code>value</code>) from this dictionary. This method does nothing |
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146 * if the <code>key</code> is not in this dictionary. |
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147 * |
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148 * @param key the key that needs to be removed. |
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149 * @return the value to which the <code>key</code> had been mapped in this |
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150 * dictionary, or <code>null</code> if the key did not have a |
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151 * mapping. |
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152 * @exception NullPointerException if <tt>key</tt> is <tt>null</tt>. |
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153 */ |
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154 abstract public V remove(Object key); |
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155 } |