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1 : dl 1.38 /*
2 : jsr166 1.121 * Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
3 : jsr166 1.67 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 : dl 1.38 *
5 : jsr166 1.67 * This code is free software; you can redistribute it and/or modify it
6 :     * under the terms of the GNU General Public License version 2 only, as
7 : dl 1.81 * published by the Free Software Foundation. Oracle designates this
8 : jsr166 1.67 * particular file as subject to the "Classpath" exception as provided
9 : dl 1.81 * by Oracle in the LICENSE file that accompanied this code.
10 : jsr166 1.67 *
11 :     * This code is distributed in the hope that it will be useful, but WITHOUT
12 :     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 :     * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 :     * version 2 for more details (a copy is included in the LICENSE file that
15 :     * accompanied this code).
16 :     *
17 :     * You should have received a copy of the GNU General Public License version
18 :     * 2 along with this work; if not, write to the Free Software Foundation,
19 :     * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 :     *
21 : jsr166 1.71 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 :     * or visit www.oracle.com if you need additional information or have any
23 :     * questions.
24 : dl 1.38 */
25 :    
26 :     package java.util;
27 : jsr166 1.102
28 : dl 1.89 import java.util.function.Consumer;
29 : jsr166 1.128 import java.util.function.Predicate;
30 : jsr166 1.120 import jdk.internal.misc.SharedSecrets;
31 : tim 1.1
32 :     /**
33 : jsr166 1.63 * An unbounded priority {@linkplain Queue queue} based on a priority heap.
34 :     * The elements of the priority queue are ordered according to their
35 :     * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
36 :     * provided at queue construction time, depending on which constructor is
37 :     * used. A priority queue does not permit {@code null} elements.
38 :     * A priority queue relying on natural ordering also does not permit
39 :     * insertion of non-comparable objects (doing so may result in
40 :     * {@code ClassCastException}).
41 : dl 1.40 *
42 : dl 1.41 * <p>The <em>head</em> of this queue is the <em>least</em> element
43 :     * with respect to the specified ordering. If multiple elements are
44 :     * tied for least value, the head is one of those elements -- ties are
45 : jsr166 1.63 * broken arbitrarily. The queue retrieval operations {@code poll},
46 :     * {@code remove}, {@code peek}, and {@code element} access the
47 : dl 1.42 * element at the head of the queue.
48 : tim 1.14 *
49 : dl 1.41 * <p>A priority queue is unbounded, but has an internal
50 :     * <i>capacity</i> governing the size of an array used to store the
51 : dl 1.40 * elements on the queue. It is always at least as large as the queue
52 :     * size. As elements are added to a priority queue, its capacity
53 :     * grows automatically. The details of the growth policy are not
54 :     * specified.
55 : tim 1.2 *
56 : dl 1.50 * <p>This class and its iterator implement all of the
57 :     * <em>optional</em> methods of the {@link Collection} and {@link
58 : dl 1.52 * Iterator} interfaces. The Iterator provided in method {@link
59 : jsr166 1.111 * #iterator()} and the Spliterator provided in method {@link #spliterator()}
60 :     * are <em>not</em> guaranteed to traverse the elements of
61 : dl 1.52 * the priority queue in any particular order. If you need ordered
62 : jsr166 1.63 * traversal, consider using {@code Arrays.sort(pq.toArray())}.
63 : dl 1.29 *
64 : jsr166 1.82 * <p><strong>Note that this implementation is not synchronized.</strong>
65 : jsr166 1.63 * Multiple threads should not access a {@code PriorityQueue}
66 :     * instance concurrently if any of the threads modifies the queue.
67 :     * Instead, use the thread-safe {@link
68 : dl 1.88 * java.util.concurrent.PriorityBlockingQueue} class.
69 : dl 1.29 *
70 : jsr166 1.63 * <p>Implementation note: this implementation provides
71 : jsr166 1.98 * O(log(n)) time for the enqueuing and dequeuing methods
72 : jsr166 1.63 * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
73 :     * linear time for the {@code remove(Object)} and {@code contains(Object)}
74 :     * methods; and constant time for the retrieval methods
75 :     * ({@code peek}, {@code element}, and {@code size}).
76 : tim 1.2 *
77 :     * <p>This class is a member of the
78 : jsr166 1.119 * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
79 : tim 1.2 * Java Collections Framework</a>.
80 : jsr166 1.63 *
81 : dl 1.7 * @since 1.5
82 : jsr166 1.63 * @author Josh Bloch, Doug Lea
83 : jsr166 1.101 * @param <E> the type of elements held in this queue
84 : tim 1.2 */
85 : jsr166 1.124 @SuppressWarnings("unchecked")
86 : tim 1.2 public class PriorityQueue<E> extends AbstractQueue<E>
87 : dl 1.47 implements java.io.Serializable {
88 : dholmes 1.11
89 : dl 1.31 private static final long serialVersionUID = -7720805057305804111L;
90 : dl 1.30
91 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
92 : tim 1.1
93 : tim 1.2 /**
94 : dl 1.55 * Priority queue represented as a balanced binary heap: the two
95 :     * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
96 :     * priority queue is ordered by comparator, or by the elements'
97 :     * natural ordering, if comparator is null: For each node n in the
98 :     * heap and each descendant d of n, n <= d. The element with the
99 :     * lowest value is in queue[0], assuming the queue is nonempty.
100 : tim 1.2 */
101 : dl 1.81 transient Object[] queue; // non-private to simplify nested class access
102 : tim 1.1
103 : tim 1.2 /**
104 :     * The number of elements in the priority queue.
105 :     */
106 : jsr166 1.107 int size;
107 : tim 1.1
108 : tim 1.2 /**
109 :     * The comparator, or null if priority queue uses elements'
110 :     * natural ordering.
111 :     */
112 : tim 1.16 private final Comparator<? super E> comparator;
113 : tim 1.2
114 :     /**
115 :     * The number of times this priority queue has been
116 :     * <i>structurally modified</i>. See AbstractList for gory details.
117 :     */
118 : jsr166 1.106 transient int modCount; // non-private to simplify nested class access
119 : tim 1.2
120 :     /**
121 : jsr166 1.63 * Creates a {@code PriorityQueue} with the default initial
122 : dl 1.52 * capacity (11) that orders its elements according to their
123 :     * {@linkplain Comparable natural ordering}.
124 : tim 1.2 */
125 :     public PriorityQueue() {
126 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
127 : tim 1.1 }
128 : tim 1.2
129 :     /**
130 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial
131 : dl 1.52 * capacity that orders its elements according to their
132 :     * {@linkplain Comparable natural ordering}.
133 : tim 1.2 *
134 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
135 : jsr166 1.63 * @throws IllegalArgumentException if {@code initialCapacity} is less
136 :     * than 1
137 : tim 1.2 */
138 :     public PriorityQueue(int initialCapacity) {
139 :     this(initialCapacity, null);
140 : tim 1.1 }
141 : tim 1.2
142 :     /**
143 : jsr166 1.106 * Creates a {@code PriorityQueue} with the default initial capacity and
144 :     * whose elements are ordered according to the specified comparator.
145 :     *
146 :     * @param comparator the comparator that will be used to order this
147 :     * priority queue. If {@code null}, the {@linkplain Comparable
148 :     * natural ordering} of the elements will be used.
149 :     * @since 1.8
150 :     */
151 :     public PriorityQueue(Comparator<? super E> comparator) {
152 :     this(DEFAULT_INITIAL_CAPACITY, comparator);
153 :     }
154 :    
155 :     /**
156 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial capacity
157 : tim 1.2 * that orders its elements according to the specified comparator.
158 :     *
159 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
160 : jsr166 1.63 * @param comparator the comparator that will be used to order this
161 :     * priority queue. If {@code null}, the {@linkplain Comparable
162 :     * natural ordering} of the elements will be used.
163 :     * @throws IllegalArgumentException if {@code initialCapacity} is
164 : dl 1.52 * less than 1
165 : tim 1.2 */
166 : dl 1.52 public PriorityQueue(int initialCapacity,
167 : dholmes 1.23 Comparator<? super E> comparator) {
168 : dl 1.55 // Note: This restriction of at least one is not actually needed,
169 :     // but continues for 1.5 compatibility
170 : tim 1.2 if (initialCapacity < 1)
171 : dholmes 1.15 throw new IllegalArgumentException();
172 : dl 1.55 this.queue = new Object[initialCapacity];
173 : tim 1.2 this.comparator = comparator;
174 : tim 1.1 }
175 : jsr166 1.56
176 : dl 1.22 /**
177 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
178 :     * specified collection. If the specified collection is an instance of
179 :     * a {@link SortedSet} or is another {@code PriorityQueue}, this
180 :     * priority queue will be ordered according to the same ordering.
181 :     * Otherwise, this priority queue will be ordered according to the
182 :     * {@linkplain Comparable natural ordering} of its elements.
183 : tim 1.2 *
184 : dl 1.52 * @param c the collection whose elements are to be placed
185 :     * into this priority queue
186 : tim 1.2 * @throws ClassCastException if elements of the specified collection
187 :     * cannot be compared to one another according to the priority
188 : dl 1.52 * queue's ordering
189 :     * @throws NullPointerException if the specified collection or any
190 :     * of its elements are null
191 : tim 1.2 */
192 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
193 : jsr166 1.70 if (c instanceof SortedSet<?>) {
194 :     SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
195 :     this.comparator = (Comparator<? super E>) ss.comparator();
196 :     initElementsFromCollection(ss);
197 :     }
198 :     else if (c instanceof PriorityQueue<?>) {
199 :     PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
200 :     this.comparator = (Comparator<? super E>) pq.comparator();
201 :     initFromPriorityQueue(pq);
202 :     }
203 : dl 1.55 else {
204 : jsr166 1.70 this.comparator = null;
205 :     initFromCollection(c);
206 : tim 1.2 }
207 : dl 1.22 }
208 :    
209 :     /**
210 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
211 : dl 1.55 * specified priority queue. This priority queue will be
212 : dl 1.52 * ordered according to the same ordering as the given priority
213 :     * queue.
214 :     *
215 :     * @param c the priority queue whose elements are to be placed
216 :     * into this priority queue
217 : jsr166 1.63 * @throws ClassCastException if elements of {@code c} cannot be
218 :     * compared to one another according to {@code c}'s
219 : dl 1.52 * ordering
220 :     * @throws NullPointerException if the specified priority queue or any
221 :     * of its elements are null
222 : dl 1.22 */
223 :     public PriorityQueue(PriorityQueue<? extends E> c) {
224 : jsr166 1.70 this.comparator = (Comparator<? super E>) c.comparator();
225 :     initFromPriorityQueue(c);
226 : dl 1.22 }
227 : dholmes 1.18
228 : dl 1.22 /**
229 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
230 :     * specified sorted set. This priority queue will be ordered
231 : dl 1.52 * according to the same ordering as the given sorted set.
232 :     *
233 :     * @param c the sorted set whose elements are to be placed
234 : jsr166 1.63 * into this priority queue
235 : dl 1.52 * @throws ClassCastException if elements of the specified sorted
236 :     * set cannot be compared to one another according to the
237 :     * sorted set's ordering
238 :     * @throws NullPointerException if the specified sorted set or any
239 :     * of its elements are null
240 : dl 1.22 */
241 :     public PriorityQueue(SortedSet<? extends E> c) {
242 : jsr166 1.70 this.comparator = (Comparator<? super E>) c.comparator();
243 :     initElementsFromCollection(c);
244 :     }
245 :    
246 : jsr166 1.125 /** Ensures that queue[0] exists, helping peek() and poll(). */
247 :     private static Object[] ensureNonEmpty(Object[] es) {
248 :     return (es.length > 0) ? es : new Object[1];
249 :     }
250 :    
251 : jsr166 1.70 private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
252 :     if (c.getClass() == PriorityQueue.class) {
253 : jsr166 1.125 this.queue = ensureNonEmpty(c.toArray());
254 : jsr166 1.70 this.size = c.size();
255 :     } else {
256 :     initFromCollection(c);
257 :     }
258 :     }
259 :    
260 :     private void initElementsFromCollection(Collection<? extends E> c) {
261 : jsr166 1.124 Object[] es = c.toArray();
262 :     int len = es.length;
263 : jsr166 1.70 // If c.toArray incorrectly doesn't return Object[], copy it.
264 : jsr166 1.124 if (es.getClass() != Object[].class)
265 :     es = Arrays.copyOf(es, len, Object[].class);
266 : jsr166 1.70 if (len == 1 || this.comparator != null)
267 : jsr166 1.124 for (Object e : es)
268 : jsr166 1.106 if (e == null)
269 : jsr166 1.70 throw new NullPointerException();
270 : jsr166 1.125 this.queue = ensureNonEmpty(es);
271 : jsr166 1.124 this.size = len;
272 : tim 1.1 }
273 :    
274 : dl 1.22 /**
275 : jsr166 1.63 * Initializes queue array with elements from the given Collection.
276 :     *
277 : dl 1.55 * @param c the collection
278 : dl 1.22 */
279 : dl 1.55 private void initFromCollection(Collection<? extends E> c) {
280 : jsr166 1.70 initElementsFromCollection(c);
281 :     heapify();
282 : jsr166 1.56 }
283 : dl 1.55
284 :     /**
285 : jsr166 1.70 * The maximum size of array to allocate.
286 :     * Some VMs reserve some header words in an array.
287 :     * Attempts to allocate larger arrays may result in
288 :     * OutOfMemoryError: Requested array size exceeds VM limit
289 :     */
290 :     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
291 :    
292 :     /**
293 : dl 1.55 * Increases the capacity of the array.
294 :     *
295 :     * @param minCapacity the desired minimum capacity
296 :     */
297 :     private void grow(int minCapacity) {
298 : jsr166 1.68 int oldCapacity = queue.length;
299 : dl 1.55 // Double size if small; else grow by 50%
300 : jsr166 1.70 int newCapacity = oldCapacity + ((oldCapacity < 64) ?
301 :     (oldCapacity + 2) :
302 :     (oldCapacity >> 1));
303 :     // overflow-conscious code
304 :     if (newCapacity - MAX_ARRAY_SIZE > 0)
305 :     newCapacity = hugeCapacity(minCapacity);
306 : dl 1.55 queue = Arrays.copyOf(queue, newCapacity);
307 : dl 1.22 }
308 : dl 1.36
309 : jsr166 1.70 private static int hugeCapacity(int minCapacity) {
310 :     if (minCapacity < 0) // overflow
311 :     throw new OutOfMemoryError();
312 :     return (minCapacity > MAX_ARRAY_SIZE) ?
313 :     Integer.MAX_VALUE :
314 :     MAX_ARRAY_SIZE;
315 :     }
316 :    
317 : tim 1.2 /**
318 : dl 1.42 * Inserts the specified element into this priority queue.
319 : tim 1.2 *
320 : jsr166 1.63 * @return {@code true} (as specified by {@link Collection#add})
321 : dl 1.52 * @throws ClassCastException if the specified element cannot be
322 :     * compared with elements currently in this priority queue
323 :     * according to the priority queue's ordering
324 :     * @throws NullPointerException if the specified element is null
325 : tim 1.2 */
326 : dl 1.52 public boolean add(E e) {
327 :     return offer(e);
328 :     }
329 :    
330 :     /**
331 :     * Inserts the specified element into this priority queue.
332 :     *
333 : jsr166 1.63 * @return {@code true} (as specified by {@link Queue#offer})
334 : dl 1.52 * @throws ClassCastException if the specified element cannot be
335 :     * compared with elements currently in this priority queue
336 :     * according to the priority queue's ordering
337 :     * @throws NullPointerException if the specified element is null
338 :     */
339 :     public boolean offer(E e) {
340 :     if (e == null)
341 : dholmes 1.11 throw new NullPointerException();
342 :     modCount++;
343 : dl 1.55 int i = size;
344 :     if (i >= queue.length)
345 :     grow(i + 1);
346 : jsr166 1.109 siftUp(i, e);
347 : dl 1.55 size = i + 1;
348 : dholmes 1.11 return true;
349 :     }
350 :    
351 : dl 1.40 public E peek() {
352 : jsr166 1.125 return (E) queue[0];
353 : tim 1.1 }
354 :    
355 : dl 1.52 private int indexOf(Object o) {
356 : jsr166 1.68 if (o != null) {
357 : jsr166 1.123 final Object[] es = queue;
358 :     for (int i = 0, n = size; i < n; i++)
359 :     if (o.equals(es[i]))
360 : dl 1.55 return i;
361 :     }
362 : dl 1.52 return -1;
363 :     }
364 :    
365 :     /**
366 :     * Removes a single instance of the specified element from this queue,
367 : jsr166 1.63 * if it is present. More formally, removes an element {@code e} such
368 :     * that {@code o.equals(e)}, if this queue contains one or more such
369 :     * elements. Returns {@code true} if and only if this queue contained
370 :     * the specified element (or equivalently, if this queue changed as a
371 :     * result of the call).
372 : dl 1.52 *
373 :     * @param o element to be removed from this queue, if present
374 : jsr166 1.63 * @return {@code true} if this queue changed as a result of the call
375 : dl 1.52 */
376 :     public boolean remove(Object o) {
377 : jsr166 1.68 int i = indexOf(o);
378 :     if (i == -1)
379 :     return false;
380 :     else {
381 :     removeAt(i);
382 :     return true;
383 :     }
384 : dl 1.52 }
385 : dholmes 1.11
386 : jsr166 1.56 /**
387 : jsr166 1.123 * Identity-based version for use in Itr.remove.
388 : jsr166 1.56 *
389 : dl 1.55 * @param o element to be removed from this queue, if present
390 :     */
391 : jsr166 1.123 void removeEq(Object o) {
392 :     final Object[] es = queue;
393 :     for (int i = 0, n = size; i < n; i++) {
394 :     if (o == es[i]) {
395 : dl 1.55 removeAt(i);
396 : jsr166 1.123 break;
397 : dl 1.55 }
398 :     }
399 :     }
400 :    
401 : dholmes 1.11 /**
402 : jsr166 1.63 * Returns {@code true} if this queue contains the specified element.
403 :     * More formally, returns {@code true} if and only if this queue contains
404 :     * at least one element {@code e} such that {@code o.equals(e)}.
405 : dholmes 1.23 *
406 : dl 1.52 * @param o object to be checked for containment in this queue
407 : jsr166 1.63 * @return {@code true} if this queue contains the specified element
408 : dholmes 1.11 */
409 : dl 1.52 public boolean contains(Object o) {
410 : jsr166 1.100 return indexOf(o) >= 0;
411 : tim 1.14 }
412 : dholmes 1.11
413 : dl 1.49 /**
414 : jsr166 1.63 * Returns an array containing all of the elements in this queue.
415 : dl 1.52 * The elements are in no particular order.
416 :     *
417 :     * <p>The returned array will be "safe" in that no references to it are
418 : jsr166 1.63 * maintained by this queue. (In other words, this method must allocate
419 : dl 1.52 * a new array). The caller is thus free to modify the returned array.
420 :     *
421 : jsr166 1.63 * <p>This method acts as bridge between array-based and collection-based
422 :     * APIs.
423 :     *
424 : jsr166 1.59 * @return an array containing all of the elements in this queue
425 : dl 1.49 */
426 : dl 1.52 public Object[] toArray() {
427 : dl 1.55 return Arrays.copyOf(queue, size);
428 : dl 1.52 }
429 : tim 1.2
430 : dl 1.52 /**
431 : jsr166 1.63 * Returns an array containing all of the elements in this queue; the
432 :     * runtime type of the returned array is that of the specified array.
433 :     * The returned array elements are in no particular order.
434 :     * If the queue fits in the specified array, it is returned therein.
435 :     * Otherwise, a new array is allocated with the runtime type of the
436 :     * specified array and the size of this queue.
437 : dl 1.52 *
438 :     * <p>If the queue fits in the specified array with room to spare
439 :     * (i.e., the array has more elements than the queue), the element in
440 :     * the array immediately following the end of the collection is set to
441 : jsr166 1.63 * {@code null}.
442 :     *
443 :     * <p>Like the {@link #toArray()} method, this method acts as bridge between
444 :     * array-based and collection-based APIs. Further, this method allows
445 :     * precise control over the runtime type of the output array, and may,
446 :     * under certain circumstances, be used to save allocation costs.
447 :     *
448 : jsr166 1.80 * <p>Suppose {@code x} is a queue known to contain only strings.
449 : jsr166 1.63 * The following code can be used to dump the queue into a newly
450 : jsr166 1.80 * allocated array of {@code String}:
451 : jsr166 1.63 *
452 : jsr166 1.104 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
453 : jsr166 1.63 *
454 : jsr166 1.80 * Note that {@code toArray(new Object[0])} is identical in function to
455 :     * {@code toArray()}.
456 : dl 1.52 *
457 :     * @param a the array into which the elements of the queue are to
458 :     * be stored, if it is big enough; otherwise, a new array of the
459 :     * same runtime type is allocated for this purpose.
460 : jsr166 1.63 * @return an array containing all of the elements in this queue
461 : dl 1.52 * @throws ArrayStoreException if the runtime type of the specified array
462 :     * is not a supertype of the runtime type of every element in
463 :     * this queue
464 :     * @throws NullPointerException if the specified array is null
465 :     */
466 :     public <T> T[] toArray(T[] a) {
467 : jsr166 1.85 final int size = this.size;
468 : dl 1.52 if (a.length < size)
469 :     // Make a new array of a's runtime type, but my contents:
470 : dl 1.55 return (T[]) Arrays.copyOf(queue, size, a.getClass());
471 : jsr166 1.68 System.arraycopy(queue, 0, a, 0, size);
472 : dl 1.52 if (a.length > size)
473 :     a[size] = null;
474 :     return a;
475 : tim 1.1 }
476 : tim 1.2
477 : dholmes 1.23 /**
478 :     * Returns an iterator over the elements in this queue. The iterator
479 :     * does not return the elements in any particular order.
480 :     *
481 : dl 1.52 * @return an iterator over the elements in this queue
482 : dholmes 1.23 */
483 : tim 1.2 public Iterator<E> iterator() {
484 : dl 1.7 return new Itr();
485 : tim 1.2 }
486 :    
487 : dl 1.55 private final class Itr implements Iterator<E> {
488 : dl 1.7 /**
489 :     * Index (into queue array) of element to be returned by
490 : tim 1.2 * subsequent call to next.
491 : dl 1.7 */
492 : jsr166 1.99 private int cursor;
493 : tim 1.2
494 : dl 1.7 /**
495 : dl 1.36 * Index of element returned by most recent call to next,
496 :     * unless that element came from the forgetMeNot list.
497 : dl 1.55 * Set to -1 if element is deleted by a call to remove.
498 : dl 1.7 */
499 : dl 1.55 private int lastRet = -1;
500 : dl 1.7
501 :     /**
502 : dl 1.55 * A queue of elements that were moved from the unvisited portion of
503 : dl 1.36 * the heap into the visited portion as a result of "unlucky" element
504 :     * removals during the iteration. (Unlucky element removals are those
505 : dl 1.55 * that require a siftup instead of a siftdown.) We must visit all of
506 : dl 1.36 * the elements in this list to complete the iteration. We do this
507 :     * after we've completed the "normal" iteration.
508 :     *
509 :     * We expect that most iterations, even those involving removals,
510 : jsr166 1.63 * will not need to store elements in this field.
511 : dl 1.36 */
512 : jsr166 1.99 private ArrayDeque<E> forgetMeNot;
513 : dl 1.36
514 :     /**
515 :     * Element returned by the most recent call to next iff that
516 :     * element was drawn from the forgetMeNot list.
517 :     */
518 : jsr166 1.99 private E lastRetElt;
519 : dl 1.55
520 :     /**
521 :     * The modCount value that the iterator believes that the backing
522 : jsr166 1.63 * Queue should have. If this expectation is violated, the iterator
523 : dl 1.55 * has detected concurrent modification.
524 :     */
525 :     private int expectedModCount = modCount;
526 : dl 1.35
527 : jsr166 1.117 Itr() {} // prevent access constructor creation
528 :    
529 : dl 1.7 public boolean hasNext() {
530 : jsr166 1.56 return cursor < size ||
531 : dl 1.55 (forgetMeNot != null && !forgetMeNot.isEmpty());
532 : dl 1.7 }
533 :    
534 :     public E next() {
535 : dl 1.55 if (expectedModCount != modCount)
536 :     throw new ConcurrentModificationException();
537 : jsr166 1.56 if (cursor < size)
538 : dl 1.55 return (E) queue[lastRet = cursor++];
539 :     if (forgetMeNot != null) {
540 :     lastRet = -1;
541 :     lastRetElt = forgetMeNot.poll();
542 : jsr166 1.56 if (lastRetElt != null)
543 : dl 1.55 return lastRetElt;
544 : dl 1.36 }
545 : dl 1.55 throw new NoSuchElementException();
546 : dl 1.7 }
547 : tim 1.2
548 : dl 1.7 public void remove() {
549 : dl 1.55 if (expectedModCount != modCount)
550 :     throw new ConcurrentModificationException();
551 :     if (lastRet != -1) {
552 : dl 1.36 E moved = PriorityQueue.this.removeAt(lastRet);
553 : dl 1.55 lastRet = -1;
554 : jsr166 1.56 if (moved == null)
555 : dl 1.36 cursor--;
556 : dl 1.55 else {
557 : dl 1.36 if (forgetMeNot == null)
558 : dl 1.89 forgetMeNot = new ArrayDeque<>();
559 : dl 1.36 forgetMeNot.add(moved);
560 : jsr166 1.56 }
561 : jsr166 1.63 } else if (lastRetElt != null) {
562 : dl 1.55 PriorityQueue.this.removeEq(lastRetElt);
563 : dl 1.36 lastRetElt = null;
564 : jsr166 1.63 } else {
565 :     throw new IllegalStateException();
566 : jsr166 1.68 }
567 : tim 1.2 expectedModCount = modCount;
568 : dl 1.7 }
569 : tim 1.2 }
570 :    
571 : tim 1.1 public int size() {
572 : tim 1.2 return size;
573 : tim 1.1 }
574 : tim 1.2
575 :     /**
576 : dl 1.52 * Removes all of the elements from this priority queue.
577 : dl 1.49 * The queue will be empty after this call returns.
578 : tim 1.2 */
579 :     public void clear() {
580 :     modCount++;
581 : jsr166 1.123 final Object[] es = queue;
582 :     for (int i = 0, n = size; i < n; i++)
583 :     es[i] = null;
584 : tim 1.2 size = 0;
585 :     }
586 :    
587 : dl 1.40 public E poll() {
588 : jsr166 1.125 final Object[] es;
589 :     final E result;
590 :    
591 :     if ((result = (E) ((es = queue)[0])) != null) {
592 :     modCount++;
593 :     final int n;
594 :     final E x = (E) es[(n = --size)];
595 :     es[n] = null;
596 :     if (n > 0) {
597 :     final Comparator<? super E> cmp;
598 :     if ((cmp = comparator) == null)
599 :     siftDownComparable(0, x, es, n);
600 :     else
601 :     siftDownUsingComparator(0, x, es, n, cmp);
602 :     }
603 :     }
604 : dl 1.36 return result;
605 :     }
606 :    
607 :     /**
608 : dl 1.55 * Removes the ith element from queue.
609 : tim 1.2 *
610 : dl 1.55 * Normally this method leaves the elements at up to i-1,
611 :     * inclusive, untouched. Under these circumstances, it returns
612 :     * null. Occasionally, in order to maintain the heap invariant,
613 :     * it must swap a later element of the list with one earlier than
614 :     * i. Under these circumstances, this method returns the element
615 :     * that was previously at the end of the list and is now at some
616 :     * position before i. This fact is used by iterator.remove so as to
617 : jsr166 1.63 * avoid missing traversing elements.
618 : tim 1.2 */
619 : jsr166 1.107 E removeAt(int i) {
620 : jsr166 1.74 // assert i >= 0 && i < size;
621 : jsr166 1.126 final Object[] es = queue;
622 : tim 1.2 modCount++;
623 : dl 1.55 int s = --size;
624 :     if (s == i) // removed last element
625 : jsr166 1.126 es[i] = null;
626 : dl 1.55 else {
627 : jsr166 1.127 E moved = (E) es[s];
628 : jsr166 1.126 es[s] = null;
629 : dl 1.55 siftDown(i, moved);
630 : jsr166 1.126 if (es[i] == moved) {
631 : dl 1.55 siftUp(i, moved);
632 : jsr166 1.126 if (es[i] != moved)
633 : dl 1.36 return moved;
634 :     }
635 : dl 1.35 }
636 : dl 1.36 return null;
637 : tim 1.1 }
638 :    
639 : tim 1.2 /**
640 : dl 1.55 * Inserts item x at position k, maintaining heap invariant by
641 :     * promoting x up the tree until it is greater than or equal to
642 :     * its parent, or is the root.
643 :     *
644 : jsr166 1.116 * To simplify and speed up coercions and comparisons, the
645 : dl 1.55 * Comparable and Comparator versions are separated into different
646 :     * methods that are otherwise identical. (Similarly for siftDown.)
647 : jsr166 1.56 *
648 : dl 1.55 * @param k the position to fill
649 :     * @param x the item to insert
650 :     */
651 :     private void siftUp(int k, E x) {
652 : jsr166 1.56 if (comparator != null)
653 : jsr166 1.124 siftUpUsingComparator(k, x, queue, comparator);
654 : dl 1.55 else
655 : jsr166 1.124 siftUpComparable(k, x, queue);
656 : dl 1.55 }
657 :    
658 : jsr166 1.124 private static <T> void siftUpComparable(int k, T x, Object[] es) {
659 :     Comparable<? super T> key = (Comparable<? super T>) x;
660 : dl 1.55 while (k > 0) {
661 :     int parent = (k - 1) >>> 1;
662 : jsr166 1.124 Object e = es[parent];
663 :     if (key.compareTo((T) e) >= 0)
664 : dl 1.55 break;
665 : jsr166 1.124 es[k] = e;
666 : dl 1.55 k = parent;
667 :     }
668 : jsr166 1.124 es[k] = key;
669 : dl 1.55 }
670 :    
671 : jsr166 1.124 private static <T> void siftUpUsingComparator(
672 :     int k, T x, Object[] es, Comparator<? super T> cmp) {
673 : dl 1.55 while (k > 0) {
674 :     int parent = (k - 1) >>> 1;
675 : jsr166 1.124 Object e = es[parent];
676 :     if (cmp.compare(x, (T) e) >= 0)
677 : dl 1.55 break;
678 : jsr166 1.124 es[k] = e;
679 : dl 1.55 k = parent;
680 :     }
681 : jsr166 1.124 es[k] = x;
682 : dl 1.55 }
683 :    
684 :     /**
685 :     * Inserts item x at position k, maintaining heap invariant by
686 :     * demoting x down the tree repeatedly until it is less than or
687 :     * equal to its children or is a leaf.
688 :     *
689 :     * @param k the position to fill
690 :     * @param x the item to insert
691 :     */
692 :     private void siftDown(int k, E x) {
693 : jsr166 1.56 if (comparator != null)
694 : jsr166 1.124 siftDownUsingComparator(k, x, queue, size, comparator);
695 : dl 1.55 else
696 : jsr166 1.124 siftDownComparable(k, x, queue, size);
697 : dl 1.55 }
698 :    
699 : jsr166 1.124 private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
700 :     // assert n > 0;
701 :     Comparable<? super T> key = (Comparable<? super T>)x;
702 :     int half = n >>> 1; // loop while a non-leaf
703 : dl 1.55 while (k < half) {
704 :     int child = (k << 1) + 1; // assume left child is least
705 : jsr166 1.124 Object c = es[child];
706 : dl 1.55 int right = child + 1;
707 : jsr166 1.124 if (right < n &&
708 :     ((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
709 :     c = es[child = right];
710 :     if (key.compareTo((T) c) <= 0)
711 : dl 1.55 break;
712 : jsr166 1.124 es[k] = c;
713 : dl 1.55 k = child;
714 :     }
715 : jsr166 1.124 es[k] = key;
716 : dl 1.55 }
717 :    
718 : jsr166 1.124 private static <T> void siftDownUsingComparator(
719 :     int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
720 :     // assert n > 0;
721 :     int half = n >>> 1;
722 : dl 1.55 while (k < half) {
723 :     int child = (k << 1) + 1;
724 : jsr166 1.124 Object c = es[child];
725 : dl 1.55 int right = child + 1;
726 : jsr166 1.124 if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
727 :     c = es[child = right];
728 :     if (cmp.compare(x, (T) c) <= 0)
729 : dl 1.55 break;
730 : jsr166 1.124 es[k] = c;
731 : dl 1.55 k = child;
732 : tim 1.2 }
733 : jsr166 1.124 es[k] = x;
734 : dl 1.36 }
735 : dl 1.35
736 : dl 1.36 /**
737 :     * Establishes the heap invariant (described above) in the entire tree,
738 :     * assuming nothing about the order of the elements prior to the call.
739 : jsr166 1.112 * This classic algorithm due to Floyd (1964) is known to be O(size).
740 : dl 1.36 */
741 :     private void heapify() {
742 : jsr166 1.114 final Object[] es = queue;
743 : jsr166 1.124 int n = size, i = (n >>> 1) - 1;
744 : jsr166 1.125 final Comparator<? super E> cmp;
745 :     if ((cmp = comparator) == null)
746 : jsr166 1.118 for (; i >= 0; i--)
747 : jsr166 1.124 siftDownComparable(i, (E) es[i], es, n);
748 : jsr166 1.114 else
749 : jsr166 1.118 for (; i >= 0; i--)
750 : jsr166 1.124 siftDownUsingComparator(i, (E) es[i], es, n, cmp);
751 : tim 1.2 }
752 :    
753 : dholmes 1.23 /**
754 : dl 1.52 * Returns the comparator used to order the elements in this
755 : jsr166 1.63 * queue, or {@code null} if this queue is sorted according to
756 : dl 1.52 * the {@linkplain Comparable natural ordering} of its elements.
757 :     *
758 :     * @return the comparator used to order this queue, or
759 : jsr166 1.63 * {@code null} if this queue is sorted according to the
760 :     * natural ordering of its elements
761 : dholmes 1.23 */
762 : tim 1.16 public Comparator<? super E> comparator() {
763 : tim 1.2 return comparator;
764 :     }
765 : dl 1.5
766 :     /**
767 : jsr166 1.77 * Saves this queue to a stream (that is, serializes it).
768 : dl 1.5 *
769 : jsr166 1.110 * @param s the stream
770 :     * @throws java.io.IOException if an I/O error occurs
771 : dl 1.5 * @serialData The length of the array backing the instance is
772 : jsr166 1.63 * emitted (int), followed by all of its elements
773 :     * (each an {@code Object}) in the proper order.
774 : dl 1.5 */
775 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
776 : jsr166 1.75 throws java.io.IOException {
777 : dl 1.7 // Write out element count, and any hidden stuff
778 :     s.defaultWriteObject();
779 : dl 1.5
780 : jsr166 1.63 // Write out array length, for compatibility with 1.5 version
781 :     s.writeInt(Math.max(2, size + 1));
782 : dl 1.5
783 : jsr166 1.64 // Write out all elements in the "proper order".
784 : jsr166 1.123 final Object[] es = queue;
785 :     for (int i = 0, n = size; i < n; i++)
786 :     s.writeObject(es[i]);
787 : dl 1.5 }
788 :    
789 :     /**
790 : dl 1.81 * Reconstitutes the {@code PriorityQueue} instance from a stream
791 :     * (that is, deserializes it).
792 :     *
793 :     * @param s the stream
794 : jsr166 1.97 * @throws ClassNotFoundException if the class of a serialized object
795 :     * could not be found
796 :     * @throws java.io.IOException if an I/O error occurs
797 : dl 1.5 */
798 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
799 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
800 : dl 1.7 // Read in size, and any hidden stuff
801 :     s.defaultReadObject();
802 : dl 1.5
803 : jsr166 1.63 // Read in (and discard) array length
804 :     s.readInt();
805 :    
806 : jsr166 1.120 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
807 : jsr166 1.125 final Object[] es = queue = new Object[Math.max(size, 1)];
808 : dl 1.5
809 : jsr166 1.64 // Read in all elements.
810 : jsr166 1.123 for (int i = 0, n = size; i < n; i++)
811 :     es[i] = s.readObject();
812 : jsr166 1.64
813 : jsr166 1.68 // Elements are guaranteed to be in "proper order", but the
814 :     // spec has never explained what that might be.
815 :     heapify();
816 : dl 1.5 }
817 : dl 1.81
818 : jsr166 1.106 /**
819 :     * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
820 :     * and <em>fail-fast</em> {@link Spliterator} over the elements in this
821 : jsr166 1.111 * queue. The spliterator does not traverse elements in any particular order
822 :     * (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
823 : jsr166 1.106 *
824 :     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
825 :     * {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
826 :     * Overriding implementations should document the reporting of additional
827 :     * characteristic values.
828 :     *
829 :     * @return a {@code Spliterator} over the elements in this queue
830 :     * @since 1.8
831 :     */
832 :     public final Spliterator<E> spliterator() {
833 : jsr166 1.113 return new PriorityQueueSpliterator(0, -1, 0);
834 : dl 1.81 }
835 :    
836 : jsr166 1.113 final class PriorityQueueSpliterator implements Spliterator<E> {
837 : dl 1.89 private int index; // current index, modified on advance/split
838 :     private int fence; // -1 until first use
839 :     private int expectedModCount; // initialized when fence set
840 : dl 1.81
841 : jsr166 1.108 /** Creates new spliterator covering the given range. */
842 : jsr166 1.113 PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
843 : dl 1.89 this.index = origin;
844 :     this.fence = fence;
845 : dl 1.81 this.expectedModCount = expectedModCount;
846 :     }
847 :    
848 : dl 1.89 private int getFence() { // initialize fence to size on first use
849 :     int hi;
850 :     if ((hi = fence) < 0) {
851 : jsr166 1.113 expectedModCount = modCount;
852 :     hi = fence = size;
853 : dl 1.89 }
854 :     return hi;
855 :     }
856 : jsr166 1.90
857 : jsr166 1.113 public PriorityQueueSpliterator trySplit() {
858 : dl 1.89 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
859 : dl 1.81 return (lo >= mid) ? null :
860 : jsr166 1.113 new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
861 : dl 1.81 }
862 :    
863 : dl 1.95 public void forEachRemaining(Consumer<? super E> action) {
864 : dl 1.89 if (action == null)
865 : dl 1.81 throw new NullPointerException();
866 : jsr166 1.115 if (fence < 0) { fence = size; expectedModCount = modCount; }
867 : jsr166 1.124 final Object[] es = queue;
868 : jsr166 1.115 int i, hi; E e;
869 :     for (i = index, index = hi = fence; i < hi; i++) {
870 : jsr166 1.124 if ((e = (E) es[i]) == null)
871 : jsr166 1.115 break; // must be CME
872 :     action.accept(e);
873 : dl 1.81 }
874 : jsr166 1.115 if (modCount != expectedModCount)
875 :     throw new ConcurrentModificationException();
876 : dl 1.81 }
877 :    
878 : dl 1.89 public boolean tryAdvance(Consumer<? super E> action) {
879 : jsr166 1.106 if (action == null)
880 :     throw new NullPointerException();
881 : jsr166 1.115 if (fence < 0) { fence = size; expectedModCount = modCount; }
882 :     int i;
883 :     if ((i = index) < fence) {
884 :     index = i + 1;
885 :     E e;
886 :     if ((e = (E) queue[i]) == null
887 :     || modCount != expectedModCount)
888 : dl 1.89 throw new ConcurrentModificationException();
889 :     action.accept(e);
890 : dl 1.81 return true;
891 :     }
892 :     return false;
893 :     }
894 :    
895 : jsr166 1.90 public long estimateSize() {
896 : jsr166 1.113 return getFence() - index;
897 : dl 1.89 }
898 :    
899 :     public int characteristics() {
900 :     return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
901 :     }
902 : dl 1.81 }
903 : jsr166 1.122
904 :     /**
905 :     * @throws NullPointerException {@inheritDoc}
906 :     */
907 : jsr166 1.128 public boolean removeIf(Predicate<? super E> filter) {
908 :     Objects.requireNonNull(filter);
909 :     return bulkRemove(filter);
910 :     }
911 :    
912 :     /**
913 :     * @throws NullPointerException {@inheritDoc}
914 :     */
915 :     public boolean removeAll(Collection<?> c) {
916 :     Objects.requireNonNull(c);
917 :     return bulkRemove(e -> c.contains(e));
918 :     }
919 :    
920 :     /**
921 :     * @throws NullPointerException {@inheritDoc}
922 :     */
923 :     public boolean retainAll(Collection<?> c) {
924 :     Objects.requireNonNull(c);
925 :     return bulkRemove(e -> !c.contains(e));
926 :     }
927 :    
928 :     // A tiny bit set implementation
929 :    
930 :     private static long[] nBits(int n) {
931 :     return new long[((n - 1) >> 6) + 1];
932 :     }
933 :     private static void setBit(long[] bits, int i) {
934 :     bits[i >> 6] |= 1L << i;
935 :     }
936 :     private static boolean isClear(long[] bits, int i) {
937 :     return (bits[i >> 6] & (1L << i)) == 0;
938 :     }
939 :    
940 :     /** Implementation of bulk remove methods. */
941 :     private boolean bulkRemove(Predicate<? super E> filter) {
942 :     final int expectedModCount = ++modCount;
943 :     final Object[] es = queue;
944 :     final int end = size;
945 :     int i;
946 :     // Optimize for initial run of survivors
947 :     for (i = 0; i < end && !filter.test((E) es[i]); i++)
948 :     ;
949 :     if (i >= end) {
950 :     if (modCount != expectedModCount)
951 :     throw new ConcurrentModificationException();
952 :     return false;
953 :     }
954 :     // Tolerate predicates that reentrantly access the collection for
955 :     // read (but writers still get CME), so traverse once to find
956 :     // elements to delete, a second pass to physically expunge.
957 :     final int beg = i;
958 :     final long[] deathRow = nBits(end - beg);
959 :     deathRow[0] = 1L; // set bit 0
960 :     for (i = beg + 1; i < end; i++)
961 :     if (filter.test((E) es[i]))
962 :     setBit(deathRow, i - beg);
963 :     if (modCount != expectedModCount)
964 :     throw new ConcurrentModificationException();
965 :     int w = beg;
966 :     for (i = beg; i < end; i++)
967 :     if (isClear(deathRow, i - beg))
968 :     es[w++] = es[i];
969 :     for (i = size = w; i < end; i++)
970 :     es[i] = null;
971 :     heapify();
972 :     return true;
973 :     }
974 :    
975 :     /**
976 :     * @throws NullPointerException {@inheritDoc}
977 :     */
978 : jsr166 1.122 public void forEach(Consumer<? super E> action) {
979 :     Objects.requireNonNull(action);
980 :     final int expectedModCount = modCount;
981 :     final Object[] es = queue;
982 :     for (int i = 0, n = size; i < n; i++)
983 :     action.accept((E) es[i]);
984 :     if (expectedModCount != modCount)
985 :     throw new ConcurrentModificationException();
986 :     }
987 : tim 1.1 }

Doug Lea
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