net.sourceforge.phpeclipse/src/net/sourceforge/phpdt/internal/core/util/SimpleLookupTable.java

   1 /*******************************************************************************
   2  * Copyright (c) 2000, 2003 IBM Corporation and others.
   3  * All rights reserved. This program and the accompanying materials
   4  * are made available under the terms of the Common Public License v1.0
   5  * which accompanies this distribution, and is available at
   6  * http://www.eclipse.org/legal/cpl-v10.html
   7  *
   8  * Contributors:
   9  *     IBM Corporation - initial API and implementation
  10  *******************************************************************************/
  11 package net.sourceforge.phpdt.internal.core.util;
  12
  13 /**
  14  * A simple lookup table is a non-synchronized Hashtable, whose keys and values
  15  * are Objects. It also uses linear probing to resolve collisions rather than a
  16  * linked list of hash table entries.
  17  */
  18 public final class SimpleLookupTable implements Cloneable {
  19
  20         // to avoid using Enumerations, walk the individual tables skipping nulls
  21         public Object[] keyTable;
  22
  23         public Object[] valueTable;
  24
  25         public int elementSize; // number of elements in the table
  26
  27         public int threshold;
  28
  29         public SimpleLookupTable() {
  30                 this(13);
  31         }
  32
  33         public SimpleLookupTable(int size) {
  34                 if (size < 3)
  35                         size = 3;
  36                 this.elementSize = 0;
  37                 this.threshold = size + 1; // size is the expected number of elements
  38                 int tableLength = 2 * size + 1;
  39                 this.keyTable = new Object[tableLength];
  40                 this.valueTable = new Object[tableLength];
  41         }
  42
  43         public Object clone() throws CloneNotSupportedException {
  44                 SimpleLookupTable result = (SimpleLookupTable) super.clone();
  45                 result.elementSize = this.elementSize;
  46                 result.threshold = this.threshold;
  47
  48                 int length = this.keyTable.length;
  49                 result.keyTable = new Object[length];
  50                 System.arraycopy(this.keyTable, 0, result.keyTable, 0, length);
  51
  52                 length = this.valueTable.length;
  53                 result.valueTable = new Object[length];
  54                 System.arraycopy(this.valueTable, 0, result.valueTable, 0, length);
  55                 return result;
  56         }
  57
  58         public boolean containsKey(Object key) {
  59                 int length = keyTable.length;
  60                 int index = (key.hashCode() & 0x7FFFFFFF) % length;
  61                 Object currentKey;
  62                 while ((currentKey = keyTable[index]) != null) {
  63                         if (currentKey.equals(key))
  64                                 return true;
  65                         if (++index == length)
  66                                 index = 0;
  67                 }
  68                 return false;
  69         }
  70
  71         public Object get(Object key) {
  72                 int length = keyTable.length;
  73                 int index = (key.hashCode() & 0x7FFFFFFF) % length;
  74                 Object currentKey;
  75                 while ((currentKey = keyTable[index]) != null) {
  76                         if (currentKey.equals(key))
  77                                 return valueTable[index];
  78                         if (++index == length)
  79                                 index = 0;
  80                 }
  81                 return null;
  82         }
  83
  84         public Object keyForValue(Object valueToMatch) {
  85                 if (valueToMatch != null)
  86                         for (int i = 0, l = valueTable.length; i < l; i++)
  87                                 if (valueToMatch.equals(valueTable[i]))
  88                                         return keyTable[i];
  89                 return null;
  90         }
  91
  92         public Object put(Object key, Object value) {
  93                 int length = keyTable.length;
  94                 int index = (key.hashCode() & 0x7FFFFFFF) % length;
  95                 Object currentKey;
  96                 while ((currentKey = keyTable[index]) != null) {
  97                         if (currentKey.equals(key))
  98                                 return valueTable[index] = value;
  99                         if (++index == length)
 100                                 index = 0;
 101                 }
 102                 keyTable[index] = key;
 103                 valueTable[index] = value;
 104
 105                 // assumes the threshold is never equal to the size of the table
 106                 if (++elementSize > threshold)
 107                         rehash();
 108                 return value;
 109         }
 110
 111         public Object removeKey(Object key) {
 112                 int length = keyTable.length;
 113                 int index = (key.hashCode() & 0x7FFFFFFF) % length;
 114                 Object currentKey;
 115                 while ((currentKey = keyTable[index]) != null) {
 116                         if (currentKey.equals(key)) {
 117                                 elementSize--;
 118                                 Object oldValue = valueTable[index];
 119                                 keyTable[index] = null;
 120                                 valueTable[index] = null;
 121                                 if (keyTable[index + 1 == length ? 0 : index + 1] != null)
 122                                         rehash(); // only needed if a possible collision existed
 123                                 return oldValue;
 124                         }
 125                         if (++index == length)
 126                                 index = 0;
 127                 }
 128                 return null;
 129         }
 130
 131         public void removeValue(Object valueToRemove) {
 132                 boolean rehash = false;
 133                 for (int i = 0, l = valueTable.length; i < l; i++) {
 134                         Object value = valueTable[i];
 135                         if (value != null && value.equals(valueToRemove)) {
 136                                 elementSize--;
 137                                 keyTable[i] = null;
 138                                 valueTable[i] = null;
 139                                 if (!rehash && keyTable[i + 1 == l ? 0 : i + 1] != null)
 140                                         rehash = true; // only needed if a possible collision
 141                                                                         // existed
 142                         }
 143                 }
 144                 if (rehash)
 145                         rehash();
 146         }
 147
 148         private void rehash() {
 149                 SimpleLookupTable newLookupTable = new SimpleLookupTable(
 150                                 elementSize * 2); // double the number of expected elements
 151                 Object currentKey;
 152                 for (int i = keyTable.length; --i >= 0;)
 153                         if ((currentKey = keyTable[i]) != null)
 154                                 newLookupTable.put(currentKey, valueTable[i]);
 155
 156                 this.keyTable = newLookupTable.keyTable;
 157                 this.valueTable = newLookupTable.valueTable;
 158                 this.elementSize = newLookupTable.elementSize;
 159                 this.threshold = newLookupTable.threshold;
 160         }
 161
 162         public String toString() {
 163                 String s = ""; //$NON-NLS-1$
 164                 Object object;
 165                 for (int i = 0, l = valueTable.length; i < l; i++)
 166                         if ((object = valueTable[i]) != null)
 167                                 s += keyTable[i].toString() + " -> " + object.toString() + "\n"; //$NON-NLS-2$ //$NON-NLS-1$
 168                 return s;
 169         }
 170 }