IntObjectHashMap


1   
2   /*
3    * Copyright (c) 1998 - 2005 Versant Corporation
4    * All rights reserved. This program and the accompanying materials
5    * are made available under the terms of the Eclipse Public License v1.0
6    * which accompanies this distribution, and is available at
7    * http://www.eclipse.org/legal/epl-v10.html
8    *
9    * Contributors:
10   * Versant Corporation - initial API and implementation
11   */
12  package com.versant.core.util;
13  
14  import java.io.IOException  ;
15  import java.io.Serializable  ;
16  
17  /**
18   * Specialized HashMap mapping int to Object. This is a cut and paste of
19   * java.util.HashMap with the key hardcoded as int and some non-required
20   * functionality removed.
21   */
22  public final class IntObjectHashMap implements Serializable   {
23  
24      /**
25       * The default initial capacity - MUST be a power of two.
26       */
27      private static final int DEFAULT_INITIAL_CAPACITY = 16;
28  
29      /**
30       * The maximum capacity, used if a higher value is implicitly specified
31       * by either of the constructors with arguments.
32       * MUST be a power of two <= 1<<30.
33       */
34      private static final int MAXIMUM_CAPACITY = 1 << 30;
35  
36      /**
37       * The load factor used when none specified in constructor.
38       */
39      private static final float DEFAULT_LOAD_FACTOR = 0.75f;
40  
41      /**
42       * The table, resized as necessary. Length MUST Always be a power of two.
43       */
44      private transient Entry[] table;
45  
46      /**
47       * The number of key-value mappings contained in this identity hash map.
48       */
49      private transient int size;
50  
51      /**
52       * The next size value at which to resize (capacity * load factor).
53       *
54       * @serial
55       */
56      private int threshold;
57  
58      /**
59       * The load factor for the hash table.
60       *
61       * @serial
62       */
63      private final float loadFactor;
64  
65      /**
66       * Constructs an empty <tt>IntObjectHashMap</tt> with the specified initial
67       * capacity and load factor.
68       *
69       * @param initialCapacity The initial capacity.
70       * @param loadFactor      The load factor.
71       * @throws IllegalArgumentException if the initial capacity is negative
72       *                                  or the load factor is nonpositive.
73       */
74      public IntObjectHashMap(int initialCapacity, float loadFactor) {
75          if (initialCapacity < 0) {
76              throw new IllegalArgumentException  ("Illegal initial capacity: " +
77                      initialCapacity);
78          }
79          if (initialCapacity > MAXIMUM_CAPACITY) {
80              initialCapacity = MAXIMUM_CAPACITY;
81          }
82          if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
83              throw new IllegalArgumentException  ("Illegal load factor: " +
84                      loadFactor);
85          }
86  
87          // Find a power of 2 >= initialCapacity
88          int capacity = 1;
89          while (capacity < initialCapacity) {
90              capacity <<= 1;
91          }
92  
93          this.loadFactor = loadFactor;
94          threshold = (int)(capacity * loadFactor);
95          table = new Entry[capacity];
96      }
97  
98      /**
99       * Constructs an empty <tt>IntObjectHashMap</tt> with the specified initial
100      * capacity and the default load factor (0.75).
101      *
102      * @param initialCapacity the initial capacity.
103      * @throws IllegalArgumentException if the initial capacity is negative.
104      */
105     public IntObjectHashMap(int initialCapacity) {
106         this(initialCapacity, DEFAULT_LOAD_FACTOR);
107     }
108 
109     /**
110      * Constructs an empty <tt>IntObjectHashMap</tt> with the default initial capacity
111      * (16) and the default load factor (0.75).
112      */
113     public IntObjectHashMap() {
114         this.loadFactor = DEFAULT_LOAD_FACTOR;
115         threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
116         table = new Entry[DEFAULT_INITIAL_CAPACITY];
117     }
118 
119     /**
120      * Returns a string representation of this map.  The string representation
121      * consists of a list of key-value mappings in the order returned by the
122      * map's <tt>entrySet</tt> view's iterator, enclosed in braces
123      * (<tt>"{}"</tt>).  Adjacent mappings are separated by the characters
124      * <tt>", "</tt> (comma and space).  Each key-value mapping is rendered as
125      * the key followed by an equals sign (<tt>"="</tt>) followed by the
126      * associated value.  Keys and values are converted to strings as by
127      * <tt>String.valueOf(Object)</tt>.<p>
128      * <p/>
129      * This implementation creates an empty string buffer, appends a left
130      * brace, and iterates over the map's <tt>entrySet</tt> view, appending
131      * the string representation of each <tt>map.entry</tt> in turn.  After
132      * appending each entry except the last, the string <tt>", "</tt> is
133      * appended.  Finally a right brace is appended.  A string is obtained
134      * from the stringbuffer, and returned.
135      *
136      * @return a String representation of this map.
137      */
138     public String   toString() {
139         StringBuffer   buf = new StringBuffer  ();
140         buf.append("{");
141         for (int i = 0; i < table.length; i++) {
142             Entry e = table[i];
143             for (; e != null; e = e.next) {
144                 int key = e.key;
145                 Object   value = e.getValue();
146                 buf.append(key + "=" + (value == this ? "(this Map)" : value));
147             }
148         }
149         buf.append("}");
150         return buf.toString();
151     }
152 
153     /**
154      * Returns the number of key-value mappings in this map.
155      *
156      * @return the number of key-value mappings in this map.
157      */
158     public int size() {
159         return size;
160     }
161 
162     /**
163      * Returns <tt>true</tt> if this map contains no key-value mappings.
164      *
165      * @return <tt>true</tt> if this map contains no key-value mappings.
166      */
167     public boolean isEmpty() {
168         return size == 0;
169     }
170 
171     /**
172      * Returns the value to which the specified key is mapped in this identity
173      * hash map, or <tt>null</tt> if the map contains no mapping for this key.
174      * A return value of <tt>null</tt> does not <i>necessarily</i> indicate
175      * that the map contains no mapping for the key; it is also possible that
176      * the map explicitly maps the key to <tt>null</tt>. The
177      * <tt>containsKey</tt> method may be used to distinguish these two cases.
178      *
179      * @param key the key whose associated value is to be returned.
180      * @return the value to which this map maps the specified key, or
181      *         <tt>null</tt> if the map contains no mapping for this key.
182      */
183     public Object   get(int key) {
184         int i = key & (table.length - 1);
185         Entry e = table[i];
186         while (true) {
187             if (e == null) {
188                 return e;
189             }
190             if (key == e.key) {
191                 return e.value;
192             }
193             e = e.next;
194         }
195     }
196 
197     /**
198      * Returns <tt>true</tt> if this map contains a mapping for the
199      * specified key.
200      *
201      * @param key The key whose presence in this map is to be tested
202      * @return <tt>true</tt> if this map contains a mapping for the specified
203      *         key.
204      */
205     public boolean containsKey(int key) {
206         int i = key & (table.length - 1);
207         Entry e = table[i];
208         while (e != null) {
209             if (key == e.key) {
210                 return true;
211             }
212             e = e.next;
213         }
214         return false;
215     }
216 
217     /**
218      * Associates the specified value with the specified key in this map.
219      * If the map previously contained a mapping for this key, the old
220      * value is replaced.
221      *
222      * @param key   key with which the specified value is to be associated.
223      * @param value value to be associated with the specified key.
224      * @return previous value associated with specified key, or <tt>null</tt>
225      *         if there was no mapping for key.  A <tt>null</tt> return can
226      *         also indicate that the IntObjectHashMap previously associated
227      *         <tt>null</tt> with the specified key.
228      */
229     public Object   put(int key, Object   value) {
230         int i = key & (table.length - 1);
231         for (Entry e = table[i]; e != null; e = e.next) {
232             if (key == e.key) {
233                 Object   oldValue = e.value;
234                 e.value = value;
235                 return oldValue;
236             }
237         }
238         addEntry(key, value, i);
239         return null;
240     }
241 
242     /**
243      * This method is used instead of put by constructors and
244      * pseudoconstructors (clone, readObject).  It does not resize the table,
245      * check for comodification, etc.  It calls createEntry rather than
246      * addEntry.
247      */
248     private void putForCreate(int key, Object   value) {
249         int i = key & (table.length - 1);
250 
251         /**
252          * Look for preexisting entry for key.  This will never happen for
253          * clone or deserialize.  It will only happen for construction if the
254          * input Map is a sorted map whose ordering is inconsistent w/ equals.
255          */
256         for (Entry e = table[i]; e != null; e = e.next) {
257             if (key == e.key) {
258                 e.value = value;
259                 return;
260             }
261         }
262         createEntry(key, value, i);
263     }
264 
265     /**
266      * Rehashes the contents of this map into a new array with a
267      * larger capacity.  This method is called automatically when the
268      * number of keys in this map reaches its threshold.
269      * <p/>
270      * If current capacity is MAXIMUM_CAPACITY, this method does not
271      * resize the map, but but sets threshold to Integer.MAX_VALUE.
272      * This has the effect of preventing future calls.
273      *
274      * @param newCapacity the new capacity, MUST be a power of two;
275      *                    must be greater than current capacity unless current
276      *                    capacity is MAXIMUM_CAPACITY (in which case value
277      *                    is irrelevant).
278      */
279     private void resize(int newCapacity) {
280         Entry[] oldTable = table;
281         int oldCapacity = oldTable.length;
282         if (oldCapacity == MAXIMUM_CAPACITY) {
283             threshold = Integer.MAX_VALUE;
284             return;
285         }
286 
287         Entry[] newTable = new Entry[newCapacity];
288         transfer(newTable);
289         table = newTable;
290         threshold = (int)(newCapacity * loadFactor);
291     }
292 
293     /**
294      * Transfer all entries from current table to newTable.
295      */
296     private void transfer(Entry[] newTable) {
297         Entry[] src = table;
298         int newCapacity = newTable.length;
299         for (int j = 0; j < src.length; j++) {
300             Entry e = src[j];
301             if (e != null) {
302                 src[j] = null;
303                 do {
304                     Entry next = e.next;
305                     int i = e.key & (newCapacity - 1);
306                     e.next = newTable[i];
307                     newTable[i] = e;
308                     e = next;
309                 } while (e != null);
310             }
311         }
312     }
313 
314     /**
315      * Removes the mapping for this key from this map if present.
316      *
317      * @param key key whose mapping is to be removed from the map.
318      * @return previous value associated with specified key, or <tt>null</tt>
319      *         if there was no mapping for key.  A <tt>null</tt> return can
320      *         also indicate that the map previously associated <tt>null</tt>
321      *         with the specified key.
322      */
323     public Object   remove(int key) {
324         Entry e = removeEntryForKey(key);
325         return e == null ? e : e.value;
326     }
327 
328     /**
329      * Removes and returns the entry associated with the specified key
330      * in the IntObjectHashMap.  Returns null if the IntObjectHashMap contains no mapping
331      * for this key.
332      */
333     private Entry removeEntryForKey(int key) {
334         int i = key & (table.length - 1);
335         Entry prev = table[i];
336         Entry e = prev;
337 
338         while (e != null) {
339             Entry next = e.next;
340             if (key == e.key) {
341                 size--;
342                 if (prev == e) {
343                     table[i] = next;
344                 } else {
345                     prev.next = next;
346                 }
347                 return e;
348             }
349             prev = e;
350             e = next;
351         }
352 
353         return e;
354     }
355 
356     /**
357      * Removes all mappings from this map.
358      */
359     public void clear() {
360         Entry tab[] = table;
361         for (int i = 0; i < tab.length; i++) {
362             tab[i] = null;
363         }
364         size = 0;
365     }
366 
367     /**
368      * Returns <tt>true</tt> if this map maps one or more keys to the
369      * specified value.
370      *
371      * @param value value whose presence in this map is to be tested.
372      * @return <tt>true</tt> if this map maps one or more keys to the
373      *         specified value.
374      */
375     public boolean containsValue(Object   value) {
376         Entry tab[] = table;
377         for (int i = 0; i < tab.length; i++) {
378             for (Entry e = tab[i]; e != null; e = e.next) {
379                 if (value.equals(e.value)) {
380                     return true;
381                 }
382             }
383         }
384         return false;
385     }
386 
387     private static class Entry {
388 
389         final int key;
390         Object   value;
391         Entry next;
392 
393         /**
394          * Create new entry.
395          */
396         public Entry(int k, Object   v, Entry n) {
397             value = v;
398             next = n;
399             key = k;
400         }
401 
402         public Object   getValue() {
403             return value;
404         }
405 
406         public Object   setValue(Object   newValue) {
407             Object   oldValue = value;
408             value = newValue;
409             return oldValue;
410         }
411 
412         public boolean equals(Object   o) {
413             if (!(o instanceof Entry)) {
414                 return false;
415             }
416             Entry e = (Entry)o;
417             if (key == e.key) {
418                 if (value == e.value || (value != null && value.equals(e.value))) {
419                     return true;
420                 }
421             }
422             return false;
423         }
424 
425         public int hashCode() {
426             return key ^ (value == null ? 0 : value.hashCode());
427         }
428 
429         public String   toString() {
430             return key + "=" + getValue();
431         }
432 
433     }
434 
435     /**
436      * Add a new entry with the specified key, value and hash code to
437      * the specified bucket.  It is the responsibility of this
438      * method to resize the table if appropriate.
439      * <p/>
440      * Subclass overrides this to alter the behavior of put method.
441      */
442     private void addEntry(int key, Object   value, int bucketIndex) {
443         table[bucketIndex] = new Entry(key, value, table[bucketIndex]);
444         if (size++ >= threshold) {
445             resize(2 * table.length);
446         }
447     }
448 
449     /**
450      * Like addEntry except that this version is used when creating entries
451      * as part of Map construction or "pseudo-construction" (cloning,
452      * deserialization).  This version needn't worry about resizing the table.
453      * <p/>
454      * Subclass overrides this to alter the behavior of IntObjectHashMap(Map),
455      * clone, and readObject.
456      */
457     private void createEntry(int key, Object   value, int bucketIndex) {
458         table[bucketIndex] = new Entry(key, value, table[bucketIndex]);
459         size++;
460     }
461 
462     /**
463      * Save the state of the <tt>IntObjectHashMap</tt> instance to a stream (i.e.,
464      * serialize it).
465      *
466      * @serialData The <i>capacity</i> of the IntObjectHashMap (the length of the
467      * bucket array) is emitted (int), followed  by the
468      * <i>size</i> of the IntObjectHashMap (the number of key-value
469      * mappings), followed by the key (Object) and value (Object)
470      * for each key-value mapping represented by the IntObjectHashMap
471      * The key-value mappings are emitted in the order that they
472      * are returned by <tt>entrySet().iterator()</tt>.
473      */
474     private void writeObject(java.io.ObjectOutputStream   s)
475             throws IOException   {
476         // Write out the threshold, loadfactor, and any hidden stuff
477         s.defaultWriteObject();
478 
479         // Write out number of buckets
480         s.writeInt(table.length);
481 
482         // Write out size (number of Mappings)
483         s.writeInt(size);
484 
485         // Write out keys and values (alternating)
486         int c = 0;
487         for (int i = 0; c < size && i < table.length; i++) {
488             Entry e = table[i];
489             for (; e != null; e = e.next, ++c) {
490                 s.writeInt(e.key);
491                 s.writeObject(e.getValue());
492             }
493         }
494     }
495 
496     /**
497      * Reconstitute the <tt>IntObjectHashMap</tt> instance from a stream (i.e.,
498      * deserialize it).
499      */
500     private void readObject(java.io.ObjectInputStream   s)
501             throws IOException  , ClassNotFoundException   {
502         // Read in the threshold, loadfactor, and any hidden stuff
503         s.defaultReadObject();
504 
505         // Read in number of buckets and allocate the bucket array;
506         int numBuckets = s.readInt();
507         table = new Entry[numBuckets];
508 
509         // Read in size (number of Mappings)
510         int size = s.readInt();
511 
512         // Read the keys and values, and put the mappings in the IntObjectHashMap
513         for (int i = 0; i < size; i++) {
514             int key = s.readInt();
515             Object   value = s.readObject();
516             putForCreate(key, value);
517         }
518     }
519 
520 }
521
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