--- jsr166/src/main/java/util/PriorityQueue.java 2005/11/27 20:41:02 1.55 +++ jsr166/src/main/java/util/PriorityQueue.java 2018/03/28 02:50:41 1.121 @@ -1,28 +1,48 @@ /* - * @(#)PriorityQueue.java 1.8 05/08/27 + * Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * - * Copyright 2005 Sun Microsystems, Inc. All rights reserved. - * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. + * This code is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 only, as + * published by the Free Software Foundation. Oracle designates this + * particular file as subject to the "Classpath" exception as provided + * by Oracle in the LICENSE file that accompanied this code. + * + * This code is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License + * version 2 for more details (a copy is included in the LICENSE file that + * accompanied this code). + * + * You should have received a copy of the GNU General Public License version + * 2 along with this work; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. + * + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA + * or visit www.oracle.com if you need additional information or have any + * questions. */ package java.util; -import java.util.*; // for javadoc (till 6280605 is fixed) + +import java.util.function.Consumer; +import jdk.internal.misc.SharedSecrets; /** - * An unbounded priority {@linkplain Queue queue} based on a priority - * heap. The elements of the priority queue are ordered according to - * their {@linkplain Comparable natural ordering}, or by a {@link - * Comparator} provided at queue construction time, depending on which - * constructor is used. A priority queue does not permit - * null elements. A priority queue relying on natural - * ordering also does not permit insertion of non-comparable objects - * (doing so may result in ClassCastException). + * An unbounded priority {@linkplain Queue queue} based on a priority heap. + * The elements of the priority queue are ordered according to their + * {@linkplain Comparable natural ordering}, or by a {@link Comparator} + * provided at queue construction time, depending on which constructor is + * used. A priority queue does not permit {@code null} elements. + * A priority queue relying on natural ordering also does not permit + * insertion of non-comparable objects (doing so may result in + * {@code ClassCastException}). * *

The head of this queue is the least element * with respect to the specified ordering. If multiple elements are * tied for least value, the head is one of those elements -- ties are - * broken arbitrarily. The queue retrieval operations poll, - * remove, peek, and element access the + * broken arbitrarily. The queue retrieval operations {@code poll}, + * {@code remove}, {@code peek}, and {@code element} access the * element at the head of the queue. * *

A priority queue is unbounded, but has an internal @@ -35,30 +55,31 @@ import java.util.*; // for javadoc (till *

This class and its iterator implement all of the * optional methods of the {@link Collection} and {@link * Iterator} interfaces. The Iterator provided in method {@link - * #iterator()} is not guaranteed to traverse the elements of + * #iterator()} and the Spliterator provided in method {@link #spliterator()} + * are not guaranteed to traverse the elements of * the priority queue in any particular order. If you need ordered - * traversal, consider using Arrays.sort(pq.toArray()). + * traversal, consider using {@code Arrays.sort(pq.toArray())}. * - *

Note that this implementation is not synchronized. - * Multiple threads should not access a PriorityQueue - * instance concurrently if any of the threads modifies the list - * structurally. Instead, use the thread-safe {@link + *

Note that this implementation is not synchronized. + * Multiple threads should not access a {@code PriorityQueue} + * instance concurrently if any of the threads modifies the queue. + * Instead, use the thread-safe {@link * java.util.concurrent.PriorityBlockingQueue} class. * - *

Implementation note: this implementation provides O(log(n)) time - * for the insertion methods (offer, poll, - * remove() and add) methods; linear time for the - * remove(Object) and contains(Object) methods; and - * constant time for the retrieval methods (peek, - * element, and size). + *

Implementation note: this implementation provides + * O(log(n)) time for the enqueuing and dequeuing methods + * ({@code offer}, {@code poll}, {@code remove()} and {@code add}); + * linear time for the {@code remove(Object)} and {@code contains(Object)} + * methods; and constant time for the retrieval methods + * ({@code peek}, {@code element}, and {@code size}). * *

This class is a member of the - * + * * Java Collections Framework. + * * @since 1.5 - * @version 1.8, 08/27/05 - * @author Josh Bloch - * @param the type of elements held in this collection + * @author Josh Bloch, Doug Lea + * @param the type of elements held in this queue */ public class PriorityQueue extends AbstractQueue implements java.io.Serializable { @@ -75,12 +96,12 @@ public class PriorityQueue extends Ab * heap and each descendant d of n, n <= d. The element with the * lowest value is in queue[0], assuming the queue is nonempty. */ - private transient Object[] queue; + transient Object[] queue; // non-private to simplify nested class access /** * The number of elements in the priority queue. */ - private int size = 0; + int size; /** * The comparator, or null if priority queue uses elements' @@ -92,10 +113,10 @@ public class PriorityQueue extends Ab * The number of times this priority queue has been * structurally modified. See AbstractList for gory details. */ - private transient int modCount = 0; + transient int modCount; // non-private to simplify nested class access /** - * Creates a PriorityQueue with the default initial + * Creates a {@code PriorityQueue} with the default initial * capacity (11) that orders its elements according to their * {@linkplain Comparable natural ordering}. */ @@ -104,27 +125,40 @@ public class PriorityQueue extends Ab } /** - * Creates a PriorityQueue with the specified initial + * Creates a {@code PriorityQueue} with the specified initial * capacity that orders its elements according to their * {@linkplain Comparable natural ordering}. * * @param initialCapacity the initial capacity for this priority queue - * @throws IllegalArgumentException if initialCapacity is less - * than 1 + * @throws IllegalArgumentException if {@code initialCapacity} is less + * than 1 */ public PriorityQueue(int initialCapacity) { this(initialCapacity, null); } /** - * Creates a PriorityQueue with the specified initial capacity + * Creates a {@code PriorityQueue} with the default initial capacity and + * whose elements are ordered according to the specified comparator. + * + * @param comparator the comparator that will be used to order this + * priority queue. If {@code null}, the {@linkplain Comparable + * natural ordering} of the elements will be used. + * @since 1.8 + */ + public PriorityQueue(Comparator comparator) { + this(DEFAULT_INITIAL_CAPACITY, comparator); + } + + /** + * Creates a {@code PriorityQueue} with the specified initial capacity * that orders its elements according to the specified comparator. * * @param initialCapacity the initial capacity for this priority queue - * @param comparator the comparator that will be used to order - * this priority queue. If null, the natural - * ordering of the elements will be used. - * @throws IllegalArgumentException if initialCapacity is + * @param comparator the comparator that will be used to order this + * priority queue. If {@code null}, the {@linkplain Comparable + * natural ordering} of the elements will be used. + * @throws IllegalArgumentException if {@code initialCapacity} is * less than 1 */ public PriorityQueue(int initialCapacity, @@ -136,14 +170,14 @@ public class PriorityQueue extends Ab this.queue = new Object[initialCapacity]; this.comparator = comparator; } - + /** - * Creates a PriorityQueue containing the elements in the - * specified collection. If the specified collection is an - * instance of a {@link java.util.SortedSet} or is another - * PriorityQueue, the priority queue will be ordered - * according to the same ordering. Otherwise, this priority queue - * will be ordered according to the natural ordering of its elements. + * Creates a {@code PriorityQueue} containing the elements in the + * specified collection. If the specified collection is an instance of + * a {@link SortedSet} or is another {@code PriorityQueue}, this + * priority queue will be ordered according to the same ordering. + * Otherwise, this priority queue will be ordered according to the + * {@linkplain Comparable natural ordering} of its elements. * * @param c the collection whose elements are to be placed * into this priority queue @@ -153,69 +187,103 @@ public class PriorityQueue extends Ab * @throws NullPointerException if the specified collection or any * of its elements are null */ + @SuppressWarnings("unchecked") public PriorityQueue(Collection c) { - initFromCollection(c); - if (c instanceof SortedSet) - comparator = (Comparator) - ((SortedSet)c).comparator(); - else if (c instanceof PriorityQueue) - comparator = (Comparator) - ((PriorityQueue)c).comparator(); + if (c instanceof SortedSet) { + SortedSet ss = (SortedSet) c; + this.comparator = (Comparator) ss.comparator(); + initElementsFromCollection(ss); + } + else if (c instanceof PriorityQueue) { + PriorityQueue pq = (PriorityQueue) c; + this.comparator = (Comparator) pq.comparator(); + initFromPriorityQueue(pq); + } else { - comparator = null; - heapify(); + this.comparator = null; + initFromCollection(c); } } /** - * Creates a PriorityQueue containing the elements in the + * Creates a {@code PriorityQueue} containing the elements in the * specified priority queue. This priority queue will be * ordered according to the same ordering as the given priority * queue. * * @param c the priority queue whose elements are to be placed * into this priority queue - * @throws ClassCastException if elements of c cannot be - * compared to one another according to c's + * @throws ClassCastException if elements of {@code c} cannot be + * compared to one another according to {@code c}'s * ordering * @throws NullPointerException if the specified priority queue or any * of its elements are null */ + @SuppressWarnings("unchecked") public PriorityQueue(PriorityQueue c) { - comparator = (Comparator)c.comparator(); - initFromCollection(c); + this.comparator = (Comparator) c.comparator(); + initFromPriorityQueue(c); } /** - * Creates a PriorityQueue containing the elements in the - * specified sorted set. This priority queue will be ordered + * Creates a {@code PriorityQueue} containing the elements in the + * specified sorted set. This priority queue will be ordered * according to the same ordering as the given sorted set. * * @param c the sorted set whose elements are to be placed - * into this priority queue. + * into this priority queue * @throws ClassCastException if elements of the specified sorted * set cannot be compared to one another according to the * sorted set's ordering * @throws NullPointerException if the specified sorted set or any * of its elements are null */ + @SuppressWarnings("unchecked") public PriorityQueue(SortedSet c) { - comparator = (Comparator)c.comparator(); - initFromCollection(c); + this.comparator = (Comparator) c.comparator(); + initElementsFromCollection(c); } - /** - * Initialize queue array with elements from the given Collection. - * @param c the collection - */ - private void initFromCollection(Collection c) { + private void initFromPriorityQueue(PriorityQueue c) { + if (c.getClass() == PriorityQueue.class) { + this.queue = c.toArray(); + this.size = c.size(); + } else { + initFromCollection(c); + } + } + + private void initElementsFromCollection(Collection c) { Object[] a = c.toArray(); // If c.toArray incorrectly doesn't return Object[], copy it. if (a.getClass() != Object[].class) a = Arrays.copyOf(a, a.length, Object[].class); - queue = a; - size = a.length; - } + int len = a.length; + if (len == 1 || this.comparator != null) + for (Object e : a) + if (e == null) + throw new NullPointerException(); + this.queue = a; + this.size = a.length; + } + + /** + * Initializes queue array with elements from the given Collection. + * + * @param c the collection + */ + private void initFromCollection(Collection c) { + initElementsFromCollection(c); + heapify(); + } + + /** + * The maximum size of array to allocate. + * Some VMs reserve some header words in an array. + * Attempts to allocate larger arrays may result in + * OutOfMemoryError: Requested array size exceeds VM limit + */ + private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; /** * Increases the capacity of the array. @@ -223,22 +291,29 @@ public class PriorityQueue extends Ab * @param minCapacity the desired minimum capacity */ private void grow(int minCapacity) { - if (minCapacity < 0) // overflow - throw new OutOfMemoryError(); - int oldCapacity = queue.length; + int oldCapacity = queue.length; // Double size if small; else grow by 50% - int newCapacity = ((oldCapacity < 64)? - ((oldCapacity + 1) * 2): - ((oldCapacity * 3) / 2)); - if (newCapacity < minCapacity) - newCapacity = minCapacity; + int newCapacity = oldCapacity + ((oldCapacity < 64) ? + (oldCapacity + 2) : + (oldCapacity >> 1)); + // overflow-conscious code + if (newCapacity - MAX_ARRAY_SIZE > 0) + newCapacity = hugeCapacity(minCapacity); queue = Arrays.copyOf(queue, newCapacity); } + private static int hugeCapacity(int minCapacity) { + if (minCapacity < 0) // overflow + throw new OutOfMemoryError(); + return (minCapacity > MAX_ARRAY_SIZE) ? + Integer.MAX_VALUE : + MAX_ARRAY_SIZE; + } + /** * Inserts the specified element into this priority queue. * - * @return true (as specified by {@link Collection#add}) + * @return {@code true} (as specified by {@link Collection#add}) * @throws ClassCastException if the specified element cannot be * compared with elements currently in this priority queue * according to the priority queue's ordering @@ -251,7 +326,7 @@ public class PriorityQueue extends Ab /** * Inserts the specified element into this priority queue. * - * @return true (as specified by {@link Queue#offer}) + * @return {@code true} (as specified by {@link Queue#offer}) * @throws ClassCastException if the specified element cannot be * compared with elements currently in this priority queue * according to the priority queue's ordering @@ -264,22 +339,18 @@ public class PriorityQueue extends Ab int i = size; if (i >= queue.length) grow(i + 1); + siftUp(i, e); size = i + 1; - if (i == 0) - queue[0] = e; - else - siftUp(i, e); return true; } + @SuppressWarnings("unchecked") public E peek() { - if (size == 0) - return null; - return (E) queue[0]; + return (size == 0) ? null : (E) queue[0]; } private int indexOf(Object o) { - if (o != null) { + if (o != null) { for (int i = 0; i < size; i++) if (o.equals(queue[i])) return i; @@ -289,34 +360,35 @@ public class PriorityQueue extends Ab /** * Removes a single instance of the specified element from this queue, - * if it is present. More formally, removes an element e such - * that o.equals(e), if this queue contains one or more such - * elements. Returns true if this queue contained the specified element - * (or equivalently, if this queue changed as a result of the call). + * if it is present. More formally, removes an element {@code e} such + * that {@code o.equals(e)}, if this queue contains one or more such + * elements. Returns {@code true} if and only if this queue contained + * the specified element (or equivalently, if this queue changed as a + * result of the call). * * @param o element to be removed from this queue, if present - * @return true if this queue changed as a result of the call + * @return {@code true} if this queue changed as a result of the call */ public boolean remove(Object o) { - int i = indexOf(o); - if (i == -1) - return false; - else { - removeAt(i); - return true; - } + int i = indexOf(o); + if (i == -1) + return false; + else { + removeAt(i); + return true; + } } - /** + /** * Version of remove using reference equality, not equals. - * Needed by iterator.remove - * + * Needed by iterator.remove. + * * @param o element to be removed from this queue, if present - * @return true if removed. + * @return {@code true} if removed */ boolean removeEq(Object o) { - for (int i = 0; i < size; i++) { - if (o == queue[i]) { + for (int i = 0; i < size; i++) { + if (o == queue[i]) { removeAt(i); return true; } @@ -325,60 +397,77 @@ public class PriorityQueue extends Ab } /** - * Returns true if this queue contains the specified element. - * More formally, returns true if and only if this queue contains - * at least one element e such that o.equals(e). + * Returns {@code true} if this queue contains the specified element. + * More formally, returns {@code true} if and only if this queue contains + * at least one element {@code e} such that {@code o.equals(e)}. * * @param o object to be checked for containment in this queue - * @return true if this queue contains the specified element + * @return {@code true} if this queue contains the specified element */ public boolean contains(Object o) { - return indexOf(o) != -1; + return indexOf(o) >= 0; } /** - * Returns an array containing all of the elements in this queue, + * Returns an array containing all of the elements in this queue. * The elements are in no particular order. * *

The returned array will be "safe" in that no references to it are - * maintained by this list. (In other words, this method must allocate + * maintained by this queue. (In other words, this method must allocate * a new array). The caller is thus free to modify the returned array. * - * @return an array containing all of the elements in this queue. + *

This method acts as bridge between array-based and collection-based + * APIs. + * + * @return an array containing all of the elements in this queue */ public Object[] toArray() { return Arrays.copyOf(queue, size); } /** - * Returns an array containing all of the elements in this queue. - * The elements are in no particular order. The runtime type of - * the returned array is that of the specified array. If the queue - * fits in the specified array, it is returned therein. - * Otherwise, a new array is allocated with the runtime type of - * the specified array and the size of this queue. + * Returns an array containing all of the elements in this queue; the + * runtime type of the returned array is that of the specified array. + * The returned array elements are in no particular order. + * If the queue fits in the specified array, it is returned therein. + * Otherwise, a new array is allocated with the runtime type of the + * specified array and the size of this queue. * *

If the queue fits in the specified array with room to spare * (i.e., the array has more elements than the queue), the element in * the array immediately following the end of the collection is set to - * null. (This is useful in determining the length of the - * queue only if the caller knows that the queue does not contain - * any null elements.) + * {@code null}. + * + *

Like the {@link #toArray()} method, this method acts as bridge between + * array-based and collection-based APIs. Further, this method allows + * precise control over the runtime type of the output array, and may, + * under certain circumstances, be used to save allocation costs. + * + *

Suppose {@code x} is a queue known to contain only strings. + * The following code can be used to dump the queue into a newly + * allocated array of {@code String}: + * + * 

 {@code String[] y = x.toArray(new String[0]);}
+ * + * Note that {@code toArray(new Object[0])} is identical in function to + * {@code toArray()}. * * @param a the array into which the elements of the queue are to * be stored, if it is big enough; otherwise, a new array of the * same runtime type is allocated for this purpose. - * @return an array containing the elements of the queue + * @return an array containing all of the elements in this queue * @throws ArrayStoreException if the runtime type of the specified array * is not a supertype of the runtime type of every element in * this queue * @throws NullPointerException if the specified array is null */ + @SuppressWarnings("unchecked") public T[] toArray(T[] a) { + final int size = this.size; if (a.length < size) // Make a new array of a's runtime type, but my contents: return (T[]) Arrays.copyOf(queue, size, a.getClass()); - System.arraycopy(queue, 0, a, 0, size); + System.arraycopy(queue, 0, a, 0, size); if (a.length > size) a[size] = null; return a; @@ -399,7 +488,7 @@ public class PriorityQueue extends Ab * Index (into queue array) of element to be returned by * subsequent call to next. */ - private int cursor = 0; + private int cursor; /** * Index of element returned by most recent call to next, @@ -417,37 +506,40 @@ public class PriorityQueue extends Ab * after we've completed the "normal" iteration. * * We expect that most iterations, even those involving removals, - * will not use need to store elements in this field. + * will not need to store elements in this field. */ - private ArrayDeque forgetMeNot = null; + private ArrayDeque forgetMeNot; /** * Element returned by the most recent call to next iff that * element was drawn from the forgetMeNot list. */ - private E lastRetElt = null; + private E lastRetElt; /** * The modCount value that the iterator believes that the backing - * List should have. If this expectation is violated, the iterator + * Queue should have. If this expectation is violated, the iterator * has detected concurrent modification. */ private int expectedModCount = modCount; + Itr() {} // prevent access constructor creation + public boolean hasNext() { - return cursor < size || + return cursor < size || (forgetMeNot != null && !forgetMeNot.isEmpty()); } + @SuppressWarnings("unchecked") public E next() { if (expectedModCount != modCount) throw new ConcurrentModificationException(); - if (cursor < size) + if (cursor < size) return (E) queue[lastRet = cursor++]; if (forgetMeNot != null) { lastRet = -1; lastRetElt = forgetMeNot.poll(); - if (lastRetElt != null) + if (lastRetElt != null) return lastRetElt; } throw new NoSuchElementException(); @@ -456,25 +548,24 @@ public class PriorityQueue extends Ab public void remove() { if (expectedModCount != modCount) throw new ConcurrentModificationException(); - if (lastRet == -1 && lastRetElt == null) - throw new IllegalStateException(); if (lastRet != -1) { E moved = PriorityQueue.this.removeAt(lastRet); lastRet = -1; - if (moved == null) + if (moved == null) cursor--; else { if (forgetMeNot == null) - forgetMeNot = new ArrayDeque(); + forgetMeNot = new ArrayDeque<>(); forgetMeNot.add(moved); - } - } else { + } + } else if (lastRetElt != null) { PriorityQueue.this.removeEq(lastRetElt); lastRetElt = null; - } + } else { + throw new IllegalStateException(); + } expectedModCount = modCount; } - } public int size() { @@ -492,13 +583,14 @@ public class PriorityQueue extends Ab size = 0; } + @SuppressWarnings("unchecked") public E poll() { if (size == 0) return null; int s = --size; modCount++; - E result = (E)queue[0]; - E x = (E)queue[s]; + E result = (E) queue[0]; + E x = (E) queue[s]; queue[s] = null; if (s != 0) siftDown(0, x); @@ -515,17 +607,18 @@ public class PriorityQueue extends Ab * i. Under these circumstances, this method returns the element * that was previously at the end of the list and is now at some * position before i. This fact is used by iterator.remove so as to - * avoid missing traverseing elements. + * avoid missing traversing elements. */ - private E removeAt(int i) { - assert i >= 0 && i < size; + @SuppressWarnings("unchecked") + E removeAt(int i) { + // assert i >= 0 && i < size; modCount++; int s = --size; if (s == i) // removed last element queue[i] = null; else { E moved = (E) queue[s]; - queue[s] = null; + queue[s] = null; siftDown(i, moved); if (queue[i] == moved) { siftUp(i, moved); @@ -541,26 +634,27 @@ public class PriorityQueue extends Ab * promoting x up the tree until it is greater than or equal to * its parent, or is the root. * - * To simplify and speed up coercions and comparisons. the + * To simplify and speed up coercions and comparisons, the * Comparable and Comparator versions are separated into different * methods that are otherwise identical. (Similarly for siftDown.) - * + * * @param k the position to fill * @param x the item to insert */ private void siftUp(int k, E x) { - if (comparator != null) + if (comparator != null) siftUpUsingComparator(k, x); else siftUpComparable(k, x); } + @SuppressWarnings("unchecked") private void siftUpComparable(int k, E x) { Comparable key = (Comparable) x; while (k > 0) { int parent = (k - 1) >>> 1; Object e = queue[parent]; - if (key.compareTo((E)e) >= 0) + if (key.compareTo((E) e) >= 0) break; queue[k] = e; k = parent; @@ -568,11 +662,12 @@ public class PriorityQueue extends Ab queue[k] = key; } + @SuppressWarnings("unchecked") private void siftUpUsingComparator(int k, E x) { while (k > 0) { int parent = (k - 1) >>> 1; Object e = queue[parent]; - if (comparator.compare(x, (E)e) >= 0) + if (comparator.compare(x, (E) e) >= 0) break; queue[k] = e; k = parent; @@ -589,12 +684,13 @@ public class PriorityQueue extends Ab * @param x the item to insert */ private void siftDown(int k, E x) { - if (comparator != null) + if (comparator != null) siftDownUsingComparator(k, x); else siftDownComparable(k, x); } + @SuppressWarnings("unchecked") private void siftDownComparable(int k, E x) { Comparable key = (Comparable)x; int half = size >>> 1; // loop while a non-leaf @@ -603,9 +699,9 @@ public class PriorityQueue extends Ab Object c = queue[child]; int right = child + 1; if (right < size && - ((Comparable)c).compareTo((E)queue[right]) > 0) + ((Comparable) c).compareTo((E) queue[right]) > 0) c = queue[child = right]; - if (key.compareTo((E)c) <= 0) + if (key.compareTo((E) c) <= 0) break; queue[k] = c; k = child; @@ -613,6 +709,7 @@ public class PriorityQueue extends Ab queue[k] = key; } + @SuppressWarnings("unchecked") private void siftDownUsingComparator(int k, E x) { int half = size >>> 1; while (k < half) { @@ -620,9 +717,9 @@ public class PriorityQueue extends Ab Object c = queue[child]; int right = child + 1; if (right < size && - comparator.compare((E)c, (E)queue[right]) > 0) - c = queue[child = right]; - if (comparator.compare(x, (E)c) <= 0) + comparator.compare((E) c, (E) queue[right]) > 0) + c = queue[child = right]; + if (comparator.compare(x, (E) c) <= 0) break; queue[k] = c; k = child; @@ -633,65 +730,169 @@ public class PriorityQueue extends Ab /** * Establishes the heap invariant (described above) in the entire tree, * assuming nothing about the order of the elements prior to the call. + * This classic algorithm due to Floyd (1964) is known to be O(size). */ + @SuppressWarnings("unchecked") private void heapify() { - for (int i = (size >>> 1) - 1; i >= 0; i--) - siftDown(i, (E)queue[i]); + final Object[] es = queue; + int i = (size >>> 1) - 1; + if (comparator == null) + for (; i >= 0; i--) + siftDownComparable(i, (E) es[i]); + else + for (; i >= 0; i--) + siftDownUsingComparator(i, (E) es[i]); } /** * Returns the comparator used to order the elements in this - * queue, or null if this queue is sorted according to + * queue, or {@code null} if this queue is sorted according to * the {@linkplain Comparable natural ordering} of its elements. * * @return the comparator used to order this queue, or - * null if this queue is sorted according to the - * natural ordering of its elements. + * {@code null} if this queue is sorted according to the + * natural ordering of its elements */ public Comparator comparator() { return comparator; } /** - * Save the state of the instance to a stream (that - * is, serialize it). + * Saves this queue to a stream (that is, serializes it). * - * @serialData The length of the array backing the instance is - * emitted (int), followed by all of its elements (each an - * Object) in the proper order. * @param s the stream + * @throws java.io.IOException if an I/O error occurs + * @serialData The length of the array backing the instance is + * emitted (int), followed by all of its elements + * (each an {@code Object}) in the proper order. */ private void writeObject(java.io.ObjectOutputStream s) - throws java.io.IOException{ + throws java.io.IOException { // Write out element count, and any hidden stuff s.defaultWriteObject(); - // Write out array length - // For compatibility with 1.5 version, must be at least 2. - s.writeInt(Math.max(2, queue.length)); + // Write out array length, for compatibility with 1.5 version + s.writeInt(Math.max(2, size + 1)); - // Write out all elements in the proper order. - for (int i=0; iPriorityQueue instance from a stream - * (that is, deserialize it). + * Reconstitutes the {@code PriorityQueue} instance from a stream + * (that is, deserializes it). + * * @param s the stream + * @throws ClassNotFoundException if the class of a serialized object + * could not be found + * @throws java.io.IOException if an I/O error occurs */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in size, and any hidden stuff s.defaultReadObject(); - // Read in array length and allocate array - int arrayLength = s.readInt(); - queue = new Object[arrayLength]; - - // Read in all elements in the proper order. - for (int i=0; ilate-binding + * and fail-fast {@link Spliterator} over the elements in this + * queue. The spliterator does not traverse elements in any particular order + * (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported). + * + *

The {@code Spliterator} reports {@link Spliterator#SIZED}, + * {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}. + * Overriding implementations should document the reporting of additional + * characteristic values. + * + * @return a {@code Spliterator} over the elements in this queue + * @since 1.8 + */ + public final Spliterator spliterator() { + return new PriorityQueueSpliterator(0, -1, 0); } + final class PriorityQueueSpliterator implements Spliterator { + private int index; // current index, modified on advance/split + private int fence; // -1 until first use + private int expectedModCount; // initialized when fence set + + /** Creates new spliterator covering the given range. */ + PriorityQueueSpliterator(int origin, int fence, int expectedModCount) { + this.index = origin; + this.fence = fence; + this.expectedModCount = expectedModCount; + } + + private int getFence() { // initialize fence to size on first use + int hi; + if ((hi = fence) < 0) { + expectedModCount = modCount; + hi = fence = size; + } + return hi; + } + + public PriorityQueueSpliterator trySplit() { + int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; + return (lo >= mid) ? null : + new PriorityQueueSpliterator(lo, index = mid, expectedModCount); + } + + @SuppressWarnings("unchecked") + public void forEachRemaining(Consumer action) { + if (action == null) + throw new NullPointerException(); + if (fence < 0) { fence = size; expectedModCount = modCount; } + final Object[] a = queue; + int i, hi; E e; + for (i = index, index = hi = fence; i < hi; i++) { + if ((e = (E) a[i]) == null) + break; // must be CME + action.accept(e); + } + if (modCount != expectedModCount) + throw new ConcurrentModificationException(); + } + + @SuppressWarnings("unchecked") + public boolean tryAdvance(Consumer action) { + if (action == null) + throw new NullPointerException(); + if (fence < 0) { fence = size; expectedModCount = modCount; } + int i; + if ((i = index) < fence) { + index = i + 1; + E e; + if ((e = (E) queue[i]) == null + || modCount != expectedModCount) + throw new ConcurrentModificationException(); + action.accept(e); + return true; + } + return false; + } + + public long estimateSize() { + return getFence() - index; + } + + public int characteristics() { + return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL; + } + } }