ObjectCache


1   /*******************************************************************************
2    * Copyright (c) 2000, 2006 IBM Corporation and others.
3    * All rights reserved. This program and the accompanying materials
4    * are made available under the terms of the Eclipse Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/epl-v10.html
7    *
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  package org.eclipse.jdt.internal.compiler.codegen;
12  
13  public class ObjectCache {
14      public Object   keyTable[];
15      public int valueTable[];
16      int elementSize;
17      int threshold;
18  /**
19   * Constructs a new, empty hashtable. A default capacity is used.
20   * Note that the hashtable will automatically grow when it gets full.
21   */
22  public ObjectCache() {
23      this(13);
24  }
25  /**
26   * Constructs a new, empty hashtable with the specified initial
27   * capacity.
28   * @param initialCapacity int
29   *  the initial number of buckets
30   */
31  public ObjectCache(int initialCapacity) {
32      this.elementSize = 0;
33      this.threshold = (int) (initialCapacity * 0.66f);
34      this.keyTable = new Object  [initialCapacity];
35      this.valueTable = new int[initialCapacity];
36  }
37  /**
38   * Clears the hash table so that it has no more elements in it.
39   */
40  public void clear() {
41      for (int i = this.keyTable.length; --i >= 0;) {
42          this.keyTable[i] = null;
43          this.valueTable[i] = 0;
44      }
45      this.elementSize = 0;
46  }
47  /** Returns true if the collection contains an element for the key.
48   *
49   * @param key char[] the key that we are looking for
50   * @return boolean
51   */
52  public boolean containsKey(Object   key) {
53      int index = hashCode(key), length = this.keyTable.length;
54      while (this.keyTable[index] != null) {
55          if (this.keyTable[index] == key)
56              return true;
57          if (++index == length) {
58              index = 0;
59          }
60      }
61      return false;
62  }
63  /** Gets the object associated with the specified key in the
64   * hashtable.
65   * @param key <CODE>char[]</CODE> the specified key
66   * @return int the element for the key or -1 if the key is not
67   *  defined in the hash table.
68   */
69  public int get(Object   key) {
70      int index = hashCode(key), length = this.keyTable.length;
71      while (this.keyTable[index] != null) {
72          if (this.keyTable[index] == key)
73              return this.valueTable[index];
74          if (++index == length) {
75              index = 0;
76          }
77      }
78      return -1;
79  }
80  /**
81   * Return the hashcode for the key parameter
82   *
83   * @param key org.eclipse.jdt.internal.compiler.lookup.MethodBinding
84   * @return int
85   */
86  public int hashCode(Object   key) {
87      return (key.hashCode() & 0x7FFFFFFF) % this.keyTable.length;
88  }
89  /**
90   * Puts the specified element into the hashtable, using the specified
91   * key.  The element may be retrieved by doing a get() with the same key.
92   * The key and the element cannot be null. 
93   * 
94   * @param key <CODE>Object</CODE> the specified key in the hashtable
95   * @param value <CODE>int</CODE> the specified element
96   * @return int the old value of the key, or -1 if it did not have one.
97   */
98  public int put(Object   key, int value) { 
99      int index = hashCode(key), length = this.keyTable.length;
100     while (this.keyTable[index] != null) {
101         if (this.keyTable[index] == key)
102             return this.valueTable[index] = value;
103         if (++index == length) {
104             index = 0;
105         }
106     }
107     this.keyTable[index] = key;
108     this.valueTable[index] = value;
109 
110     // assumes the threshold is never equal to the size of the table
111     if (++this.elementSize > this.threshold)
112         rehash();
113     return value;
114 }
115 /**
116  * Rehashes the content of the table into a bigger table.
117  * This method is called automatically when the hashtable's
118  * size exceeds the threshold.
119  */
120 private void rehash() {
121     ObjectCache newHashtable = new ObjectCache(this.keyTable.length * 2);
122     for (int i = this.keyTable.length; --i >= 0;)
123         if (this.keyTable[i] != null)
124             newHashtable.put(this.keyTable[i], this.valueTable[i]);
125 
126     this.keyTable = newHashtable.keyTable;
127     this.valueTable = newHashtable.valueTable;
128     this.threshold = newHashtable.threshold;
129 }
130 /**
131  * Returns the number of elements contained in the hashtable.
132  *
133  * @return <CODE>int</CODE> The size of the table
134  */
135 public int size() {
136     return this.elementSize;
137 }
138 /**
139  * Converts to a rather lengthy String.
140  *
141  * @return String the ascii representation of the receiver
142  */
143 public String   toString() {
144     int max = size();
145     StringBuffer   buf = new StringBuffer  ();
146     buf.append("{"); //$NON-NLS-1$
147     for (int i = 0; i < max; ++i) {
148         if (this.keyTable[i] != null) {
149             buf.append(this.keyTable[i]).append("->").append(this.valueTable[i]); //$NON-NLS-1$
150         }
151         if (i < max) {
152             buf.append(", "); //$NON-NLS-1$
153         }
154     }
155     buf.append("}"); //$NON-NLS-1$
156     return buf.toString();
157 }
158 }
159
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