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1 : tim 1.2 package java.util;
2 : tim 1.1
3 :     /**
4 : dholmes 1.20 * An unbounded priority queue based on a priority heap. This queue orders
5 : brian 1.6 * elements according to an order specified at construction time, which is
6 : tim 1.19 * specified in the same manner as {@link java.util.TreeSet} and
7 : dholmes 1.18 * {@link java.util.TreeMap}: elements are ordered
8 : tim 1.2 * either according to their <i>natural order</i> (see {@link Comparable}), or
9 : tim 1.19 * according to a {@link java.util.Comparator}, depending on which
10 : dholmes 1.18 * constructor is used.
11 : tim 1.19 * <p>The <em>head</em> of this queue is the <em>least</em> element with
12 :     * respect to the specified ordering.
13 : dholmes 1.18 * If multiple elements are tied for least value, the
14 : tim 1.14 * head is one of those elements. A priority queue does not permit
15 : dholmes 1.11 * <tt>null</tt> elements.
16 : tim 1.14 *
17 : dholmes 1.11 * <p>The {@link #remove()} and {@link #poll()} methods remove and
18 :     * return the head of the queue.
19 :     *
20 :     * <p>The {@link #element()} and {@link #peek()} methods return, but do
21 :     * not delete, the head of the queue.
22 : tim 1.2 *
23 : dl 1.7 * <p>A priority queue has a <i>capacity</i>. The capacity is the
24 :     * size of the array used internally to store the elements on the
25 : dholmes 1.20 * queue.
26 : dholmes 1.18 * It is always at least as large as the queue size. As
27 : dl 1.7 * elements are added to a priority queue, its capacity grows
28 :     * automatically. The details of the growth policy are not specified.
29 : tim 1.2 *
30 : dholmes 1.11 * <p>Implementation note: this implementation provides O(log(n)) time
31 :     * for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
32 :     * <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
33 :     * <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
34 :     * constant time for the retrieval methods (<tt>peek</tt>,
35 :     * <tt>element</tt>, and <tt>size</tt>).
36 : tim 1.2 *
37 :     * <p>This class is a member of the
38 :     * <a href="{@docRoot}/../guide/collections/index.html">
39 :     * Java Collections Framework</a>.
40 : dl 1.7 * @since 1.5
41 :     * @author Josh Bloch
42 : tim 1.2 */
43 :     public class PriorityQueue<E> extends AbstractQueue<E>
44 : dholmes 1.18 implements Sorted, Queue<E>, java.io.Serializable {
45 : dholmes 1.11
46 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
47 : tim 1.1
48 : tim 1.2 /**
49 :     * Priority queue represented as a balanced binary heap: the two children
50 :     * of queue[n] are queue[2*n] and queue[2*n + 1]. The priority queue is
51 :     * ordered by comparator, or by the elements' natural ordering, if
52 : brian 1.6 * comparator is null: For each node n in the heap and each descendant d
53 :     * of n, n <= d.
54 : tim 1.2 *
55 : brian 1.6 * The element with the lowest value is in queue[1], assuming the queue is
56 :     * nonempty. (A one-based array is used in preference to the traditional
57 :     * zero-based array to simplify parent and child calculations.)
58 : tim 1.2 *
59 :     * queue.length must be >= 2, even if size == 0.
60 :     */
61 : tim 1.16 private transient Object[] queue;
62 : tim 1.1
63 : tim 1.2 /**
64 :     * The number of elements in the priority queue.
65 :     */
66 :     private int size = 0;
67 : tim 1.1
68 : tim 1.2 /**
69 :     * The comparator, or null if priority queue uses elements'
70 :     * natural ordering.
71 :     */
72 : tim 1.16 private final Comparator<? super E> comparator;
73 : tim 1.2
74 :     /**
75 :     * The number of times this priority queue has been
76 :     * <i>structurally modified</i>. See AbstractList for gory details.
77 :     */
78 : dl 1.5 private transient int modCount = 0;
79 : tim 1.2
80 :     /**
81 : dholmes 1.11 * Create a <tt>PriorityQueue</tt> with the default initial capacity
82 : dl 1.7 * (11) that orders its elements according to their natural
83 :     * ordering (using <tt>Comparable</tt>.)
84 : tim 1.2 */
85 :     public PriorityQueue() {
86 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
87 : tim 1.1 }
88 : tim 1.2
89 :     /**
90 : dholmes 1.11 * Create a <tt>PriorityQueue</tt> with the specified initial capacity
91 : dl 1.7 * that orders its elements according to their natural ordering
92 :     * (using <tt>Comparable</tt>.)
93 : tim 1.2 *
94 :     * @param initialCapacity the initial capacity for this priority queue.
95 :     */
96 :     public PriorityQueue(int initialCapacity) {
97 :     this(initialCapacity, null);
98 : tim 1.1 }
99 : tim 1.2
100 :     /**
101 : dholmes 1.11 * Create a <tt>PriorityQueue</tt> with the specified initial capacity
102 : tim 1.2 * that orders its elements according to the specified comparator.
103 :     *
104 :     * @param initialCapacity the initial capacity for this priority queue.
105 :     * @param comparator the comparator used to order this priority queue.
106 : dholmes 1.11 * If <tt>null</tt> then the order depends on the elements' natural
107 :     * ordering.
108 : dholmes 1.15 * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
109 :     * than 1
110 : tim 1.2 */
111 : tim 1.16 public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
112 : tim 1.2 if (initialCapacity < 1)
113 : dholmes 1.15 throw new IllegalArgumentException();
114 : tim 1.16 this.queue = new Object[initialCapacity + 1];
115 : tim 1.2 this.comparator = comparator;
116 : tim 1.1 }
117 :    
118 : tim 1.2 /**
119 : dholmes 1.11 * Create a <tt>PriorityQueue</tt> containing the elements in the specified
120 : tim 1.2 * collection. The priority queue has an initial capacity of 110% of the
121 : dholmes 1.20 * size of the specified collection or 1 if the collection is empty.
122 : dholmes 1.15 * If the specified collection
123 : tim 1.2 * implements the {@link Sorted} interface, the priority queue will be
124 :     * sorted according to the same comparator, or according to its elements'
125 :     * natural order if the collection is sorted according to its elements'
126 : brian 1.6 * natural order. If the specified collection does not implement
127 :     * <tt>Sorted</tt>, the priority queue is ordered according to
128 : tim 1.2 * its elements' natural order.
129 :     *
130 : dholmes 1.15 * @param c the collection whose elements are to be placed
131 : tim 1.2 * into this priority queue.
132 :     * @throws ClassCastException if elements of the specified collection
133 :     * cannot be compared to one another according to the priority
134 :     * queue's ordering.
135 : dholmes 1.15 * @throws NullPointerException if <tt>c</tt> or any element within it
136 :     * is <tt>null</tt>
137 : tim 1.2 */
138 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
139 : dholmes 1.15 int sz = c.size();
140 : tim 1.2 int initialCapacity = (int)Math.min((sz * 110L) / 100,
141 :     Integer.MAX_VALUE - 1);
142 :     if (initialCapacity < 1)
143 :     initialCapacity = 1;
144 : dholmes 1.15
145 : tim 1.16 this.queue = new Object[initialCapacity + 1];
146 : tim 1.2
147 : dholmes 1.15 if (c instanceof Sorted) {
148 : tim 1.19 comparator = (Comparator<? super E>)((Sorted)c).comparator();
149 : tim 1.2 } else {
150 :     comparator = null;
151 :     }
152 : dholmes 1.18
153 :     for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
154 :     add(i.next());
155 : tim 1.1 }
156 :    
157 : tim 1.2 // Queue Methods
158 :    
159 :     /**
160 : dholmes 1.11 * Add the specified element to this priority queue.
161 : tim 1.2 *
162 : dholmes 1.11 * @return <tt>true</tt>
163 :     * @throws ClassCastException if the specified element cannot be compared
164 :     * with elements currently in the priority queue according
165 :     * to the priority queue's ordering.
166 : dholmes 1.18 * @throws NullPointerException if the specified element is <tt>null</tt>.
167 : tim 1.2 */
168 : dholmes 1.18 public boolean offer(E o) {
169 :     if (o == null)
170 : dholmes 1.11 throw new NullPointerException();
171 :     modCount++;
172 :     ++size;
173 :    
174 :     // Grow backing store if necessary
175 :     while (size >= queue.length) {
176 : tim 1.16 Object[] newQueue = new Object[2 * queue.length];
177 : dholmes 1.11 System.arraycopy(queue, 0, newQueue, 0, queue.length);
178 :     queue = newQueue;
179 :     }
180 :    
181 : dholmes 1.18 queue[size] = o;
182 : dholmes 1.11 fixUp(size);
183 :     return true;
184 :     }
185 :    
186 : tim 1.1 public E poll() {
187 : tim 1.2 if (size == 0)
188 :     return null;
189 : tim 1.16 return (E) remove(1);
190 : tim 1.1 }
191 : tim 1.2
192 : tim 1.1 public E peek() {
193 : tim 1.16 return (E) queue[1];
194 : tim 1.1 }
195 :    
196 : tim 1.2 // Collection Methods
197 :    
198 : dholmes 1.11 // these first two override just to get the throws docs
199 :    
200 :     /**
201 :     * @throws NullPointerException if the specified element is <tt>null</tt>.
202 : dholmes 1.15 * @throws ClassCastException if the specified element cannot be compared
203 :     * with elements currently in the priority queue according
204 :     * to the priority queue's ordering.
205 : dholmes 1.11 */
206 : dholmes 1.18 public boolean add(E o) {
207 :     return super.add(o);
208 : dholmes 1.11 }
209 :    
210 : tim 1.14 /**
211 : dholmes 1.15 * @throws ClassCastException if any element cannot be compared
212 :     * with elements currently in the priority queue according
213 :     * to the priority queue's ordering.
214 : dholmes 1.18 * @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
215 :     * is <tt>null</tt>
216 : tim 1.14 */
217 :     public boolean addAll(Collection<? extends E> c) {
218 :     return super.addAll(c);
219 :     }
220 : dholmes 1.11
221 : dl 1.12 public boolean remove(Object o) {
222 : dholmes 1.11 if (o == null)
223 : dholmes 1.15 return false;
224 : tim 1.2
225 :     if (comparator == null) {
226 :     for (int i = 1; i <= size; i++) {
227 : tim 1.16 if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
228 : tim 1.2 remove(i);
229 :     return true;
230 :     }
231 :     }
232 :     } else {
233 :     for (int i = 1; i <= size; i++) {
234 : tim 1.16 if (comparator.compare((E)queue[i], (E)o) == 0) {
235 : tim 1.2 remove(i);
236 :     return true;
237 :     }
238 :     }
239 :     }
240 : tim 1.1 return false;
241 :     }
242 : tim 1.2
243 :     public Iterator<E> iterator() {
244 : dl 1.7 return new Itr();
245 : tim 1.2 }
246 :    
247 :     private class Itr implements Iterator<E> {
248 : dl 1.7 /**
249 :     * Index (into queue array) of element to be returned by
250 : tim 1.2 * subsequent call to next.
251 : dl 1.7 */
252 :     private int cursor = 1;
253 : tim 1.2
254 : dl 1.7 /**
255 :     * Index of element returned by most recent call to next or
256 :     * previous. Reset to 0 if this element is deleted by a call
257 :     * to remove.
258 :     */
259 :     private int lastRet = 0;
260 :    
261 :     /**
262 :     * The modCount value that the iterator believes that the backing
263 :     * List should have. If this expectation is violated, the iterator
264 :     * has detected concurrent modification.
265 :     */
266 :     private int expectedModCount = modCount;
267 : tim 1.2
268 : dl 1.7 public boolean hasNext() {
269 :     return cursor <= size;
270 :     }
271 :    
272 :     public E next() {
273 : tim 1.2 checkForComodification();
274 :     if (cursor > size)
275 : dl 1.7 throw new NoSuchElementException();
276 : tim 1.16 E result = (E) queue[cursor];
277 : tim 1.2 lastRet = cursor++;
278 :     return result;
279 : dl 1.7 }
280 : tim 1.2
281 : dl 1.7 public void remove() {
282 :     if (lastRet == 0)
283 :     throw new IllegalStateException();
284 : tim 1.2 checkForComodification();
285 :    
286 :     PriorityQueue.this.remove(lastRet);
287 :     if (lastRet < cursor)
288 :     cursor--;
289 :     lastRet = 0;
290 :     expectedModCount = modCount;
291 : dl 1.7 }
292 : tim 1.2
293 : dl 1.7 final void checkForComodification() {
294 :     if (modCount != expectedModCount)
295 :     throw new ConcurrentModificationException();
296 :     }
297 : tim 1.2 }
298 :    
299 :     /**
300 :     * Returns the number of elements in this priority queue.
301 : tim 1.10 *
302 : tim 1.2 * @return the number of elements in this priority queue.
303 :     */
304 : tim 1.1 public int size() {
305 : tim 1.2 return size;
306 : tim 1.1 }
307 : tim 1.2
308 :     /**
309 :     * Remove all elements from the priority queue.
310 :     */
311 :     public void clear() {
312 :     modCount++;
313 :    
314 :     // Null out element references to prevent memory leak
315 :     for (int i=1; i<=size; i++)
316 :     queue[i] = null;
317 :    
318 :     size = 0;
319 :     }
320 :    
321 :     /**
322 :     * Removes and returns the ith element from queue. Recall
323 :     * that queue is one-based, so 1 <= i <= size.
324 :     *
325 :     * XXX: Could further special-case i==size, but is it worth it?
326 :     * XXX: Could special-case i==0, but is it worth it?
327 :     */
328 :     private E remove(int i) {
329 :     assert i <= size;
330 :     modCount++;
331 :    
332 : tim 1.16 E result = (E) queue[i];
333 : tim 1.2 queue[i] = queue[size];
334 :     queue[size--] = null; // Drop extra ref to prevent memory leak
335 :     if (i <= size)
336 :     fixDown(i);
337 :     return result;
338 : tim 1.1 }
339 :    
340 : tim 1.2 /**
341 :     * Establishes the heap invariant (described above) assuming the heap
342 :     * satisfies the invariant except possibly for the leaf-node indexed by k
343 :     * (which may have a nextExecutionTime less than its parent's).
344 :     *
345 :     * This method functions by "promoting" queue[k] up the hierarchy
346 :     * (by swapping it with its parent) repeatedly until queue[k]
347 :     * is greater than or equal to its parent.
348 :     */
349 :     private void fixUp(int k) {
350 :     if (comparator == null) {
351 :     while (k > 1) {
352 :     int j = k >> 1;
353 : tim 1.16 if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
354 : tim 1.2 break;
355 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
356 : tim 1.2 k = j;
357 :     }
358 :     } else {
359 :     while (k > 1) {
360 :     int j = k >> 1;
361 : tim 1.16 if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
362 : tim 1.2 break;
363 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
364 : tim 1.2 k = j;
365 :     }
366 :     }
367 :     }
368 :    
369 :     /**
370 :     * Establishes the heap invariant (described above) in the subtree
371 :     * rooted at k, which is assumed to satisfy the heap invariant except
372 :     * possibly for node k itself (which may be greater than its children).
373 :     *
374 :     * This method functions by "demoting" queue[k] down the hierarchy
375 :     * (by swapping it with its smaller child) repeatedly until queue[k]
376 :     * is less than or equal to its children.
377 :     */
378 :     private void fixDown(int k) {
379 :     int j;
380 :     if (comparator == null) {
381 :     while ((j = k << 1) <= size) {
382 : tim 1.16 if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
383 : tim 1.2 j++; // j indexes smallest kid
384 : tim 1.16 if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
385 : tim 1.2 break;
386 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
387 : tim 1.2 k = j;
388 :     }
389 :     } else {
390 :     while ((j = k << 1) <= size) {
391 : tim 1.16 if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
392 : tim 1.2 j++; // j indexes smallest kid
393 : tim 1.16 if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
394 : tim 1.2 break;
395 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
396 : tim 1.2 k = j;
397 :     }
398 :     }
399 :     }
400 :    
401 : tim 1.16 public Comparator<? super E> comparator() {
402 : tim 1.2 return comparator;
403 :     }
404 : dl 1.5
405 :     /**
406 :     * Save the state of the instance to a stream (that
407 :     * is, serialize it).
408 :     *
409 :     * @serialData The length of the array backing the instance is
410 :     * emitted (int), followed by all of its elements (each an
411 :     * <tt>Object</tt>) in the proper order.
412 : dl 1.7 * @param s the stream
413 : dl 1.5 */
414 :     private synchronized void writeObject(java.io.ObjectOutputStream s)
415 :     throws java.io.IOException{
416 : dl 1.7 // Write out element count, and any hidden stuff
417 :     s.defaultWriteObject();
418 : dl 1.5
419 :     // Write out array length
420 :     s.writeInt(queue.length);
421 :    
422 : dl 1.7 // Write out all elements in the proper order.
423 :     for (int i=0; i<size; i++)
424 : dl 1.5 s.writeObject(queue[i]);
425 :     }
426 :    
427 :     /**
428 :     * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
429 :     * deserialize it).
430 : dl 1.7 * @param s the stream
431 : dl 1.5 */
432 :     private synchronized void readObject(java.io.ObjectInputStream s)
433 :     throws java.io.IOException, ClassNotFoundException {
434 : dl 1.7 // Read in size, and any hidden stuff
435 :     s.defaultReadObject();
436 : dl 1.5
437 :     // Read in array length and allocate array
438 :     int arrayLength = s.readInt();
439 : tim 1.16 queue = new Object[arrayLength];
440 : dl 1.5
441 : dl 1.7 // Read in all elements in the proper order.
442 :     for (int i=0; i<size; i++)
443 : tim 1.16 queue[i] = s.readObject();
444 : dl 1.5 }
445 :    
446 : tim 1.1 }
447 : dholmes 1.11

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