Mercurial > hg > truffle
annotate graal/com.oracle.max.base/src/com/sun/max/collect/IdentitySet.java @ 4184:fa6b78681c54
Added copyright check to the gate.
author | Doug Simon <doug.simon@oracle.com> |
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date | Tue, 03 Jan 2012 12:37:31 +0100 |
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rev | line source |
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1 /* |
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2 * Copyright (c) 2007, 2011, 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. |
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8 * |
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9 * This code is distributed in the hope that it will be useful, but WITHOUT |
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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12 * version 2 for more details (a copy is included in the LICENSE file that |
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13 * accompanied this code). |
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14 * |
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15 * You should have received a copy of the GNU General Public License version |
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16 * 2 along with this work; if not, write to the Free Software Foundation, |
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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18 * |
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
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22 */ |
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23 package com.sun.max.collect; |
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24 |
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25 import java.util.*; |
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26 |
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27 import com.sun.max.*; |
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28 |
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29 /** |
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30 * Similar to IdentityHashSet, but not recording 'null' as a set member |
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31 * and not providing any element removal operations. |
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32 * |
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33 * (IdentityHashSet's iterator seems to return 'null' as a member even if it has never been entered.) |
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34 */ |
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35 public class IdentitySet<T> implements Iterable<T> { |
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36 |
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37 /** |
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38 * The default initial capacity - MUST be a power of two. |
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39 */ |
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40 public static final int DEFAULT_INITIAL_CAPACITY = 16; |
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41 |
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42 /** |
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43 * The maximum capacity, used if a higher value is implicitly specified |
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44 * by either of the constructors with arguments. |
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45 * MUST be a power of two <= 1<<30. |
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46 */ |
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47 public static final int MAXIMUM_CAPACITY = 1 << 30; |
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48 |
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49 // Note: this implementation is partly derived from java.util.HashMap in the standard JDK |
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50 // In particular, it uses a table whose length is guaranteed to be a power of 2. |
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51 |
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52 /** |
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53 * The number of key-value mappings contained in this map. |
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54 */ |
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55 private int numberOfElements; |
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56 |
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57 /** |
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58 * Gets the number of key-value mappings contained in this map. |
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59 */ |
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60 public int numberOfElements() { |
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61 return numberOfElements; |
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62 } |
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63 |
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64 /** |
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65 * The table, resized as necessary. Length MUST Always be a power of two. |
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66 */ |
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67 private T[] table; |
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68 |
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69 /** |
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70 * The next size value at which to resize (capacity * load factor). |
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71 */ |
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72 private int threshold; |
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73 |
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74 private void setThreshold() { |
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75 if (table.length == 0) { |
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76 threshold = -1; |
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77 } else { |
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78 threshold = (table.length >> 2) * 3; |
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79 } |
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80 } |
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81 |
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82 /** |
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83 * Constructs a new, empty IdentitySet. |
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84 */ |
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85 public IdentitySet() { |
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86 this(DEFAULT_INITIAL_CAPACITY); |
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87 } |
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88 |
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89 /** |
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90 * Constructs a new, empty IdentitySet. |
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91 * @param initialCapacity the initial capacity of the Set |
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92 * @throws {@code IllegalArgumentException} if {@code initialCapacity} is less than zero} |
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93 */ |
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94 public IdentitySet(int initialCapacity) { |
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95 if (initialCapacity < 0) { |
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96 throw new IllegalArgumentException(); |
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97 } |
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98 // Find a power of 2 >= initialCapacity |
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99 int capacity = Integer.highestOneBit(Math.max(Math.min(MAXIMUM_CAPACITY, initialCapacity), 1)); |
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100 if (capacity < initialCapacity) { |
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101 capacity <<= 1; |
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102 } |
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103 |
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104 final Class<T[]> type = null; |
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105 table = Utils.cast(type, new Object[capacity]); |
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106 setThreshold(); |
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107 } |
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108 |
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109 private void resize(int newTableLength) { |
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110 final T[] oldTable = table; |
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111 final Class<T[]> type = null; |
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112 table = Utils.cast(type, new Object[newTableLength]); |
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113 setThreshold(); |
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114 numberOfElements = 0; |
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115 for (int i = 0; i < oldTable.length; i++) { |
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116 final T oldValue = oldTable[i]; |
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117 if (oldValue != null) { |
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118 add(oldValue); |
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119 } |
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120 } |
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121 } |
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122 |
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123 /** |
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124 * Applies a supplemental hash function to a given hashCode, which |
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125 * defends against poor quality hash functions. This is critical |
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126 * because BuckHashMapping uses power-of-two length hash tables, that |
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127 * otherwise encounter collisions for hashCodes that do not differ |
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128 * in lower bits. |
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129 */ |
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130 static int hash(int hash) { |
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131 // This function ensures that hashCodes that differ only by |
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132 // constant multiples at each bit position have a bounded |
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133 // number of collisions (approximately 8 at default load factor). |
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134 final int h = hash ^ ((hash >>> 20) ^ (hash >>> 12)); |
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135 return h ^ (h >>> 7) ^ (h >>> 4); |
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136 } |
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137 |
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138 /** |
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139 * Returns index for hash code h. |
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140 */ |
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141 static int indexFor(int h, int length) { |
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142 return h & (length - 1); |
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143 } |
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144 |
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145 /** |
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146 * Adds a given element to this set. |
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147 * |
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148 * @param element the element to add |
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149 * @throws IllegalArgumentException if {@code element == null} |
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150 */ |
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151 public void add(T element) { |
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152 if (element == null) { |
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153 throw new IllegalArgumentException("Element cannot be null"); |
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154 } |
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155 if (numberOfElements > threshold) { |
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156 resize(table.length * 2); |
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157 } |
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158 final int start = indexFor(System.identityHashCode(element), table.length); |
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159 int i = start; |
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160 do { |
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161 final T entry = table[i]; |
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162 if (entry == null) { |
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163 table[i] = element; |
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164 numberOfElements++; |
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165 return; |
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166 } |
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167 if (entry == element) { |
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168 return; |
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169 } |
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170 if (++i == table.length) { |
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171 i = 0; |
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172 } |
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173 } while (i != start); |
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174 } |
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175 |
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176 /** |
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177 * Determines if a given element is a member of this set. |
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178 * |
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179 * @param element the element to test for membership in this set |
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180 * @return {@code true} if {@code element} is in this set, {@code false} otherwise |
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181 * @throws IllegalArgumentException if {@code element == null} |
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182 */ |
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183 public boolean contains(T element) { |
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184 if (element == null) { |
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185 throw new IllegalArgumentException("Element cannot be null"); |
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186 } |
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187 if (numberOfElements == 0) { |
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188 return false; |
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189 } |
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190 final int start = indexFor(System.identityHashCode(element), table.length); |
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191 int i = start; |
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192 while (true) { |
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193 final T entry = table[i]; |
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194 if (entry == element) { |
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195 return true; |
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196 } |
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197 if (entry == null) { |
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198 return false; |
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199 } |
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200 if (++i == table.length) { |
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201 i = 0; |
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202 } |
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203 assert i != start; |
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204 } |
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205 } |
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206 |
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207 public Iterator<T> iterator() { |
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208 final Class<T[]> type = null; |
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209 final T[] array = Utils.cast(type, new Object[numberOfElements()]); |
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210 int j = 0; |
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211 for (int i = 0; i < table.length; i++) { |
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212 final T element = table[i]; |
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213 if (element != null) { |
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214 array[j++] = element; |
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215 } |
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216 } |
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217 return Arrays.asList(array).iterator(); |
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218 } |
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219 } |