IntHashtable


1   // IntHashtable - a Hashtable that uses ints as the keys
2   //
3   // This is 90% based on JavaSoft's java.util.Hashtable.
4   //
5   // Visit the ACME Labs Java page for up-to-date versions of this and other
6   // fine Java utilities: http://www.acme.com/java/
7   
8   package Acme;
9   
10  import java.util.Dictionary  ;
11  import java.util.Enumeration  ;
12  import java.util.NoSuchElementException  ;
13  
14  /// A Hashtable that uses ints as the keys.
15  // <P>
16  // Use just like java.util.Hashtable, except that the keys must be ints.
17  // This is much faster than creating a new Integer for each access.
18  // <P>
19  // <A HREF="../../resources/classes/Acme/IntHashtable.java">Fetch the software.</A><BR>
20  // <A HREF="../../resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>
21  // <P>
22  // @see java.util.Hashtable
23  
24  public class IntHashtable extends Dictionary   implements Cloneable   {
25      /// The hash table data.
26      private IntHashtableEntry table[];
27  
28      /// The total number of entries in the hash table.
29      private int count;
30  
31      /// Rehashes the table when count exceeds this threshold.
32      private int threshold;
33  
34      /// The load factor for the hashtable.
35      private float loadFactor;
36  
37      /// Constructs a new, empty hashtable with the specified initial 
38      // capacity and the specified load factor.
39      // @param initialCapacity the initial number of buckets
40      // @param loadFactor a number between 0.0 and 1.0, it defines
41      //      the threshold for rehashing the hashtable into
42      //      a bigger one.
43      // @exception IllegalArgumentException If the initial capacity
44      // is less than or equal to zero.
45      // @exception IllegalArgumentException If the load factor is
46      // less than or equal to zero.
47      public IntHashtable(int initialCapacity, float loadFactor) {
48          if (initialCapacity <= 0 || loadFactor <= 0.0)
49              throw new IllegalArgumentException  ();
50          this.loadFactor = loadFactor;
51          table = new IntHashtableEntry[initialCapacity];
52          threshold = (int) (initialCapacity * loadFactor);
53      }
54  
55      /// Constructs a new, empty hashtable with the specified initial 
56      // capacity.
57      // @param initialCapacity the initial number of buckets
58      public IntHashtable(int initialCapacity) {
59          this(initialCapacity, 0.75f);
60      }
61  
62      /// Constructs a new, empty hashtable. A default capacity and load factor
63      // is used. Note that the hashtable will automatically grow when it gets
64      // full.
65      public IntHashtable() {
66          this(101, 0.75f);
67      }
68  
69      /// Returns the number of elements contained in the hashtable. 
70      public int size() {
71          return count;
72      }
73  
74      /// Returns true if the hashtable contains no elements.
75      public boolean isEmpty() {
76          return count == 0;
77      }
78  
79      /// Returns an enumeration of the hashtable's keys.
80      // @see IntHashtable#elements
81      public synchronized Enumeration   keys() {
82          return new IntHashtableEnumerator(table, true);
83      }
84  
85      /// Returns an enumeration of the elements. Use the Enumeration methods 
86      // on the returned object to fetch the elements sequentially.
87      // @see IntHashtable#keys
88      public synchronized Enumeration   elements() {
89          return new IntHashtableEnumerator(table, false);
90      }
91  
92      /// Returns true if the specified object is an element of the hashtable.
93      // This operation is more expensive than the containsKey() method.
94      // @param value the value that we are looking for
95      // @exception NullPointerException If the value being searched 
96      // for is equal to null.
97      // @see IntHashtable#containsKey
98      public synchronized boolean contains(Object   value) {
99          if (value == null)
100             throw new NullPointerException  ();
101         IntHashtableEntry tab[] = table;
102         for (int i = tab.length; i-- > 0;) {
103             for (IntHashtableEntry e = tab[i]; e != null; e = e.next) {
104                 if (e.value.equals(value))
105                     return true;
106             }
107         }
108         return false;
109     }
110 
111     /// Returns true if the collection contains an element for the key.
112     // @param key the key that we are looking for
113     // @see IntHashtable#contains
114     public synchronized boolean containsKey(int key) {
115         IntHashtableEntry tab[] = table;
116         int hash = key;
117         int index = (hash & 0x7FFFFFFF) % tab.length;
118         for (IntHashtableEntry e = tab[index]; e != null; e = e.next) {
119             if (e.hash == hash && e.key == key)
120                 return true;
121         }
122         return false;
123     }
124 
125     /// Gets the object associated with the specified key in the 
126     // hashtable.
127     // @param key the specified key
128     // @returns the element for the key or null if the key
129     //      is not defined in the hash table.
130     // @see IntHashtable#put
131     public synchronized Object   get(int key) {
132         IntHashtableEntry tab[] = table;
133         int hash = key;
134         int index = (hash & 0x7FFFFFFF) % tab.length;
135         for (IntHashtableEntry e = tab[index]; e != null; e = e.next) {
136             if (e.hash == hash && e.key == key)
137                 return e.value;
138         }
139         return null;
140     }
141 
142     /// A get method that takes an Object, for compatibility with
143     // java.util.Dictionary.  The Object must be an Integer.
144     public Object   get(Object   okey) {
145         if (!(okey instanceof Integer  ))
146             throw new InternalError  ("key is not an Integer");
147         Integer   ikey = (Integer  ) okey;
148         int key = ikey.intValue();
149         return get(key);
150     }
151 
152     /// Rehashes the content of the table into a bigger table.
153     // This method is called automatically when the hashtable's
154     // size exceeds the threshold.
155     protected void rehash() {
156         int oldCapacity = table.length;
157         IntHashtableEntry oldTable[] = table;
158 
159         int newCapacity = oldCapacity * 2 + 1;
160         IntHashtableEntry newTable[] = new IntHashtableEntry[newCapacity];
161 
162         threshold = (int) (newCapacity * loadFactor);
163         table = newTable;
164 
165         for (int i = oldCapacity; i-- > 0;) {
166             for (IntHashtableEntry old = oldTable[i]; old != null;) {
167                 IntHashtableEntry e = old;
168                 old = old.next;
169 
170                 int index = (e.hash & 0x7FFFFFFF) % newCapacity;
171                 e.next = newTable[index];
172                 newTable[index] = e;
173             }
174         }
175     }
176 
177     /// Puts the specified element into the hashtable, using the specified
178     // key.  The element may be retrieved by doing a get() with the same key.
179     // The key and the element cannot be null. 
180     // @param key the specified key in the hashtable
181     // @param value the specified element
182     // @exception NullPointerException If the value of the element 
183     // is equal to null.
184     // @see IntHashtable#get
185     // @return the old value of the key, or null if it did not have one.
186     public synchronized Object   put(int key, Object   value) {
187         // Make sure the value is not null.
188         if (value == null)
189             throw new NullPointerException  ();
190 
191         // Makes sure the key is not already in the hashtable.
192         IntHashtableEntry tab[] = table;
193         int hash = key;
194         int index = (hash & 0x7FFFFFFF) % tab.length;
195         for (IntHashtableEntry e = tab[index]; e != null; e = e.next) {
196             if (e.hash == hash && e.key == key) {
197                 Object   old = e.value;
198                 e.value = value;
199                 return old;
200             }
201         }
202 
203         if (count >= threshold) {
204             // Rehash the table if the threshold is exceeded.
205             rehash();
206             return put(key, value);
207         }
208 
209         // Creates the new entry.
210         IntHashtableEntry e = new IntHashtableEntry();
211         e.hash = hash;
212         e.key = key;
213         e.value = value;
214         e.next = tab[index];
215         tab[index] = e;
216         ++count;
217         return null;
218     }
219 
220     /// A put method that takes an Object, for compatibility with
221     // java.util.Dictionary.  The Object must be an Integer.
222     public Object   put(Object   okey, Object   value) {
223         if (!(okey instanceof Integer  ))
224             throw new InternalError  ("key is not an Integer");
225         Integer   ikey = (Integer  ) okey;
226         int key = ikey.intValue();
227         return put(key, value);
228     }
229 
230     /// Removes the element corresponding to the key. Does nothing if the
231     // key is not present.
232     // @param key the key that needs to be removed
233     // @return the value of key, or null if the key was not found.
234     public synchronized Object   remove(int key) {
235         IntHashtableEntry tab[] = table;
236         int hash = key;
237         int index = (hash & 0x7FFFFFFF) % tab.length;
238         for (IntHashtableEntry e = tab[index], prev = null; e != null; prev = e, e = e.next) {
239             if (e.hash == hash && e.key == key) {
240                 if (prev != null)
241                     prev.next = e.next;
242                 else
243                     tab[index] = e.next;
244                 --count;
245                 return e.value;
246             }
247         }
248         return null;
249     }
250 
251     /// A remove method that takes an Object, for compatibility with
252     // java.util.Dictionary.  The Object must be an Integer.
253     public Object   remove(Object   okey) {
254         if (!(okey instanceof Integer  ))
255             throw new InternalError  ("key is not an Integer");
256         Integer   ikey = (Integer  ) okey;
257         int key = ikey.intValue();
258         return remove(key);
259     }
260 
261     /// Clears the hash table so that it has no more elements in it.
262     public synchronized void clear() {
263         IntHashtableEntry tab[] = table;
264         for (int index = tab.length; --index >= 0;)
265             tab[index] = null;
266         count = 0;
267     }
268 
269     /// Creates a clone of the hashtable. A shallow copy is made,
270     // the keys and elements themselves are NOT cloned. This is a
271     // relatively expensive operation.
272     public synchronized Object   clone() {
273         try {
274             IntHashtable t = (IntHashtable) super.clone();
275             t.table = new IntHashtableEntry[table.length];
276             for (int i = table.length; i-- > 0;)
277                 t.table[i] = (table[i] != null) ?
278                         (IntHashtableEntry) table[i].clone() : null;
279             return t;
280         } catch (CloneNotSupportedException   e) {
281             // This shouldn't happen, since we are Cloneable.
282             throw new InternalError  ();
283         }
284     }
285 
286     /// Converts to a rather lengthy String.
287     public synchronized String   toString() {
288         int max = size() - 1;
289         StringBuffer   buf = new StringBuffer  ();
290         Enumeration   k = keys();
291         Enumeration   e = elements();
292         buf.append("{");
293 
294         for (int i = 0; i <= max; ++i) {
295             String   s1 = k.nextElement().toString();
296             String   s2 = e.nextElement().toString();
297             buf.append(s1 + "=" + s2);
298             if (i < max)
299                 buf.append(", ");
300         }
301         buf.append("}");
302         return buf.toString();
303     }
304 }
305 
306 
307 class IntHashtableEntry {
308     int hash;
309     int key;
310     Object   value;
311     IntHashtableEntry next;
312 
313     protected Object   clone() {
314         IntHashtableEntry entry = new IntHashtableEntry();
315         entry.hash = hash;
316         entry.key = key;
317         entry.value = value;
318         entry.next = (next != null) ? (IntHashtableEntry) next.clone() : null;
319         return entry;
320     }
321 }
322 
323 
324 class IntHashtableEnumerator implements Enumeration   {
325     boolean keys;
326     int index;
327     IntHashtableEntry table[];
328     IntHashtableEntry entry;
329 
330     IntHashtableEnumerator(IntHashtableEntry table[], boolean keys) {
331         this.table = table;
332         this.keys = keys;
333         this.index = table.length;
334     }
335 
336     public boolean hasMoreElements() {
337         if (entry != null)
338             return true;
339         while (index-- > 0)
340             if ((entry = table[index]) != null)
341                 return true;
342         return false;
343     }
344 
345     public Object   nextElement() {
346         if (entry == null)
347             while ((index-- > 0) && ((entry = table[index]) == null))
348                 ;
349         if (entry != null) {
350             IntHashtableEntry e = entry;
351             entry = e.next;
352             return keys ? new Integer  (e.key) : e.value;
353         }
354         throw new NoSuchElementException  ("IntHashtableEnumerator");
355     }
356 }
357
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