Back to index...

	/*
	* Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* 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.function.Consumer;
	import java.util.function.Predicate;
	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 {@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}).
	*
	* <p>The <em>head</em> of this queue is the <em>least</em> 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 {@code poll},
	* {@code remove}, {@code peek}, and {@code element} access the
	* element at the head of the queue.
	*
	* <p>A priority queue is unbounded, but has an internal
	* <i>capacity</i> governing the size of an array used to store the
	* elements on the queue. It is always at least as large as the queue
	* size. As elements are added to a priority queue, its capacity
	* grows automatically. The details of the growth policy are not
	* specified.
	*
	* <p>This class and its iterator implement all of the
	* <em>optional</em> methods of the {@link Collection} and {@link
	* Iterator} interfaces. The Iterator provided in method {@link
	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
	* are <em>not</em> guaranteed to traverse the elements of
	* the priority queue in any particular order. If you need ordered
	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
	*
	* <p><strong>Note that this implementation is not synchronized.</strong>
	* 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.
	*
	* <p>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}).
	*
	* <p>This class is a member of the
	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
	* Java Collections Framework</a>.
	*
	* @since 1.5
	* @author Josh Bloch, Doug Lea
	* @param <E> the type of elements held in this queue
	*/
	@SuppressWarnings("unchecked")
	public class PriorityQueue<E> extends AbstractQueue<E>
	implements java.io.Serializable {

	private static final long serialVersionUID = -7720805057305804111L;

	private static final int DEFAULT_INITIAL_CAPACITY = 11;

	/**
	* Priority queue represented as a balanced binary heap: the two
	* children of queue[n] are queue[2n+1] and queue[2(n+1)]. The
	* priority queue is ordered by comparator, or by the elements'
	* natural ordering, if comparator is null: For each node n in the
	* heap and each descendant d of n, n <= d. The element with the
	* lowest value is in queue[0], assuming the queue is nonempty.
	*/
	transient Object[] queue; // non-private to simplify nested class access

	/**
	* The number of elements in the priority queue.
	*/
	int size;

	/**
	* The comparator, or null if priority queue uses elements'
	* natural ordering.
	*/
	private final Comparator<? super E> comparator;

	/**
	* The number of times this priority queue has been
	* <i>structurally modified</i>. See AbstractList for gory details.
	*/
	transient int modCount; // non-private to simplify nested class access

	/**
	* Creates a {@code PriorityQueue} with the default initial
	* capacity (11) that orders its elements according to their
	* {@linkplain Comparable natural ordering}.
	*/
	public PriorityQueue() {
	this(DEFAULT_INITIAL_CAPACITY, null);
	}

	/**
	* 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 {@code initialCapacity} is less
	* than 1
	*/
	public PriorityQueue(int initialCapacity) {
	this(initialCapacity, null);
	}

	/**
	* 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<? super E> 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 {@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,
	Comparator<? super E> comparator) {
	// Note: This restriction of at least one is not actually needed,
	// but continues for 1.5 compatibility
	if (initialCapacity < 1)
	throw new IllegalArgumentException();
	this.queue = new Object[initialCapacity];
	this.comparator = comparator;
	}

	/**
	* 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
	* @throws ClassCastException if elements of the specified collection
	* cannot be compared to one another according to the priority
	* queue's ordering
	* @throws NullPointerException if the specified collection or any
	* of its elements are null
	*/
	public PriorityQueue(Collection<? extends E> c) {
	if (c instanceof SortedSet<?>) {
	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
	this.comparator = (Comparator<? super E>) ss.comparator();
	initElementsFromCollection(ss);
	}
	else if (c instanceof PriorityQueue<?>) {
	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
	this.comparator = (Comparator<? super E>) pq.comparator();
	initFromPriorityQueue(pq);
	}
	else {
	this.comparator = null;
	initFromCollection(c);
	}
	}

	/**
	* 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 {@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
	*/
	public PriorityQueue(PriorityQueue<? extends E> c) {
	this.comparator = (Comparator<? super E>) c.comparator();
	initFromPriorityQueue(c);
	}

	/**
	* 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
	* @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
	*/
	public PriorityQueue(SortedSet<? extends E> c) {
	this.comparator = (Comparator<? super E>) c.comparator();
	initElementsFromCollection(c);
	}

	/** Ensures that queue[0] exists, helping peek() and poll(). */
	private static Object[] ensureNonEmpty(Object[] es) {
	return (es.length > 0) ? es : new Object[1];
	}

	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
	if (c.getClass() == PriorityQueue.class) {
	this.queue = ensureNonEmpty(c.toArray());
	this.size = c.size();
	} else {
	initFromCollection(c);
	}
	}

	private void initElementsFromCollection(Collection<? extends E> c) {
	Object[] es = c.toArray();
	int len = es.length;
	// If c.toArray incorrectly doesn't return Object[], copy it.
	if (es.getClass() != Object[].class)
	es = Arrays.copyOf(es, len, Object[].class);
	if (len == 1 \|\| this.comparator != null)
	for (Object e : es)
	if (e == null)
	throw new NullPointerException();
	this.queue = ensureNonEmpty(es);
	this.size = len;
	}

	/**
	* Initializes queue array with elements from the given Collection.
	*
	* @param c the collection
	*/
	private void initFromCollection(Collection<? extends E> 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.
	*
	* @param minCapacity the desired minimum capacity
	*/
	private void grow(int minCapacity) {
	int oldCapacity = queue.length;
	// Double size if small; else grow by 50%
	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 {@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
	* @throws NullPointerException if the specified element is null
	*/
	public boolean add(E e) {
	return offer(e);
	}

	/**
	* Inserts the specified element into this priority queue.
	*
	* @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
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offer(E e) {
	if (e == null)
	throw new NullPointerException();
	modCount++;
	int i = size;
	if (i >= queue.length)
	grow(i + 1);
	siftUp(i, e);
	size = i + 1;
	return true;
	}

	public E peek() {
	return (E) queue[0];
	}

	private int indexOf(Object o) {
	if (o != null) {
	final Object[] es = queue;
	for (int i = 0, n = size; i < n; i++)
	if (o.equals(es[i]))
	return i;
	}
	return -1;
	}

	/**
	* Removes a single instance of the specified element from this queue,
	* 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 {@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;
	}
	}

	/**
	* Identity-based version for use in Itr.remove.
	*
	* @param o element to be removed from this queue, if present
	*/
	void removeEq(Object o) {
	final Object[] es = queue;
	for (int i = 0, n = size; i < n; i++) {
	if (o == es[i]) {
	removeAt(i);
	break;
	}
	}
	}

	/**
	* 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 {@code true} if this queue contains the specified element
	*/
	public boolean contains(Object o) {
	return indexOf(o) >= 0;
	}

	/**
	* Returns an array containing all of the elements in this queue.
	* The elements are in no particular order.
	*
	* <p>The returned array will be "safe" in that no references to it are
	* maintained by this queue. (In other words, this method must allocate
	* a new array). The caller is thus free to modify the returned array.
	*
	* <p>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
	* 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.
	*
	* <p>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
	* {@code null}.
	*
	* <p>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.
	*
	* <p>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}:
	*
	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
	*
	* 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 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
	*/
	public <T> 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);
	if (a.length > size)
	a[size] = null;
	return a;
	}

	/**
	* Returns an iterator over the elements in this queue. The iterator
	* does not return the elements in any particular order.
	*
	* @return an iterator over the elements in this queue
	*/
	public Iterator<E> iterator() {
	return new Itr();
	}

	private final class Itr implements Iterator<E> {
	/**
	* Index (into queue array) of element to be returned by
	* subsequent call to next.
	*/
	private int cursor;

	/**
	* Index of element returned by most recent call to next,
	* unless that element came from the forgetMeNot list.
	* Set to -1 if element is deleted by a call to remove.
	*/
	private int lastRet = -1;

	/**
	* A queue of elements that were moved from the unvisited portion of
	* the heap into the visited portion as a result of "unlucky" element
	* removals during the iteration. (Unlucky element removals are those
	* that require a siftup instead of a siftdown.) We must visit all of
	* the elements in this list to complete the iteration. We do this
	* after we've completed the "normal" iteration.
	*
	* We expect that most iterations, even those involving removals,
	* will not need to store elements in this field.
	*/
	private ArrayDeque<E> forgetMeNot;

	/**
	* Element returned by the most recent call to next iff that
	* element was drawn from the forgetMeNot list.
	*/
	private E lastRetElt;

	/**
	* The modCount value that the iterator believes that the backing
	* 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 \|\|
	(forgetMeNot != null && !forgetMeNot.isEmpty());
	}

	public E next() {
	if (expectedModCount != modCount)
	throw new ConcurrentModificationException();
	if (cursor < size)
	return (E) queue[lastRet = cursor++];
	if (forgetMeNot != null) {
	lastRet = -1;
	lastRetElt = forgetMeNot.poll();
	if (lastRetElt != null)
	return lastRetElt;
	}
	throw new NoSuchElementException();
	}

	public void remove() {
	if (expectedModCount != modCount)
	throw new ConcurrentModificationException();
	if (lastRet != -1) {
	E moved = PriorityQueue.this.removeAt(lastRet);
	lastRet = -1;
	if (moved == null)
	cursor--;
	else {
	if (forgetMeNot == null)
	forgetMeNot = new ArrayDeque<>();
	forgetMeNot.add(moved);
	}
	} else if (lastRetElt != null) {
	PriorityQueue.this.removeEq(lastRetElt);
	lastRetElt = null;
	} else {
	throw new IllegalStateException();
	}
	expectedModCount = modCount;
	}
	}

	public int size() {
	return size;
	}

	/**
	* Removes all of the elements from this priority queue.
	* The queue will be empty after this call returns.
	*/
	public void clear() {
	modCount++;
	final Object[] es = queue;
	for (int i = 0, n = size; i < n; i++)
	es[i] = null;
	size = 0;
	}

	public E poll() {
	final Object[] es;
	final E result;

	if ((result = (E) ((es = queue)[0])) != null) {
	modCount++;
	final int n;
	final E x = (E) es[(n = --size)];
	es[n] = null;
	if (n > 0) {
	final Comparator<? super E> cmp;
	if ((cmp = comparator) == null)
	siftDownComparable(0, x, es, n);
	else
	siftDownUsingComparator(0, x, es, n, cmp);
	}
	}
	return result;
	}

	/**
	* Removes the ith element from queue.
	*
	* Normally this method leaves the elements at up to i-1,
	* inclusive, untouched. Under these circumstances, it returns
	* null. Occasionally, in order to maintain the heap invariant,
	* it must swap a later element of the list with one earlier than
	* 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 traversing elements.
	*/
	E removeAt(int i) {
	// assert i >= 0 && i < size;
	final Object[] es = queue;
	modCount++;
	int s = --size;
	if (s == i) // removed last element
	es[i] = null;
	else {
	E moved = (E) es[s];
	es[s] = null;
	siftDown(i, moved);
	if (es[i] == moved) {
	siftUp(i, moved);
	if (es[i] != moved)
	return moved;
	}
	}
	return null;
	}

	/**
	* Inserts item x at position k, maintaining heap invariant by
	* 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
	* 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)
	siftUpUsingComparator(k, x, queue, comparator);
	else
	siftUpComparable(k, x, queue);
	}

	private static <T> void siftUpComparable(int k, T x, Object[] es) {
	Comparable<? super T> key = (Comparable<? super T>) x;
	while (k > 0) {
	int parent = (k - 1) >>> 1;
	Object e = es[parent];
	if (key.compareTo((T) e) >= 0)
	break;
	es[k] = e;
	k = parent;
	}
	es[k] = key;
	}

	private static <T> void siftUpUsingComparator(
	int k, T x, Object[] es, Comparator<? super T> cmp) {
	while (k > 0) {
	int parent = (k - 1) >>> 1;
	Object e = es[parent];
	if (cmp.compare(x, (T) e) >= 0)
	break;
	es[k] = e;
	k = parent;
	}
	es[k] = x;
	}

	/**
	* Inserts item x at position k, maintaining heap invariant by
	* demoting x down the tree repeatedly until it is less than or
	* equal to its children or is a leaf.
	*
	* @param k the position to fill
	* @param x the item to insert
	*/
	private void siftDown(int k, E x) {
	if (comparator != null)
	siftDownUsingComparator(k, x, queue, size, comparator);
	else
	siftDownComparable(k, x, queue, size);
	}

	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
	// assert n > 0;
	Comparable<? super T> key = (Comparable<? super T>)x;
	int half = n >>> 1; // loop while a non-leaf
	while (k < half) {
	int child = (k << 1) + 1; // assume left child is least
	Object c = es[child];
	int right = child + 1;
	if (right < n &&
	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
	c = es[child = right];
	if (key.compareTo((T) c) <= 0)
	break;
	es[k] = c;
	k = child;
	}
	es[k] = key;
	}

	private static <T> void siftDownUsingComparator(
	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
	// assert n > 0;
	int half = n >>> 1;
	while (k < half) {
	int child = (k << 1) + 1;
	Object c = es[child];
	int right = child + 1;
	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
	c = es[child = right];
	if (cmp.compare(x, (T) c) <= 0)
	break;
	es[k] = c;
	k = child;
	}
	es[k] = x;
	}

	/**
	* 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).
	*/
	private void heapify() {
	final Object[] es = queue;
	int n = size, i = (n >>> 1) - 1;
	final Comparator<? super E> cmp;
	if ((cmp = comparator) == null)
	for (; i >= 0; i--)
	siftDownComparable(i, (E) es[i], es, n);
	else
	for (; i >= 0; i--)
	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
	}

	/**
	* Returns the comparator used to order the elements in this
	* 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
	* {@code null} if this queue is sorted according to the
	* natural ordering of its elements
	*/
	public Comparator<? super E> comparator() {
	return comparator;
	}

	/**
	* Saves this queue to a stream (that is, serializes it).
	*
	* @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 {
	// Write out element count, and any hidden stuff
	s.defaultWriteObject();

	// 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".
	final Object[] es = queue;
	for (int i = 0, n = size; i < n; i++)
	s.writeObject(es[i]);
	}

	/**
	* 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 (and discard) array length
	s.readInt();

	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
	final Object[] es = queue = new Object[Math.max(size, 1)];

	// Read in all elements.
	for (int i = 0, n = size; i < n; i++)
	es[i] = s.readObject();

	// Elements are guaranteed to be in "proper order", but the
	// spec has never explained what that might be.
	heapify();
	}

	/**
	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
	* and <em>fail-fast</em> {@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).
	*
	* <p>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<E> spliterator() {
	return new PriorityQueueSpliterator(0, -1, 0);
	}

	final class PriorityQueueSpliterator implements Spliterator<E> {
	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);
	}

	public void forEachRemaining(Consumer<? super E> action) {
	if (action == null)
	throw new NullPointerException();
	if (fence < 0) { fence = size; expectedModCount = modCount; }
	final Object[] es = queue;
	int i, hi; E e;
	for (i = index, index = hi = fence; i < hi; i++) {
	if ((e = (E) es[i]) == null)
	break; // must be CME
	action.accept(e);
	}
	if (modCount != expectedModCount)
	throw new ConcurrentModificationException();
	}

	public boolean tryAdvance(Consumer<? super E> 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;
	}
	}

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public boolean removeIf(Predicate<? super E> filter) {
	Objects.requireNonNull(filter);
	return bulkRemove(filter);
	}

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public boolean removeAll(Collection<?> c) {
	Objects.requireNonNull(c);
	return bulkRemove(e -> c.contains(e));
	}

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public boolean retainAll(Collection<?> c) {
	Objects.requireNonNull(c);
	return bulkRemove(e -> !c.contains(e));
	}

	// A tiny bit set implementation

	private static long[] nBits(int n) {
	return new long[((n - 1) >> 6) + 1];
	}
	private static void setBit(long[] bits, int i) {
	bits[i >> 6] \|= 1L << i;
	}
	private static boolean isClear(long[] bits, int i) {
	return (bits[i >> 6] & (1L << i)) == 0;
	}

	/** Implementation of bulk remove methods. */
	private boolean bulkRemove(Predicate<? super E> filter) {
	final int expectedModCount = ++modCount;
	final Object[] es = queue;
	final int end = size;
	int i;
	// Optimize for initial run of survivors
	for (i = 0; i < end && !filter.test((E) es[i]); i++)
	;
	if (i >= end) {
	if (modCount != expectedModCount)
	throw new ConcurrentModificationException();
	return false;
	}
	// Tolerate predicates that reentrantly access the collection for
	// read (but writers still get CME), so traverse once to find
	// elements to delete, a second pass to physically expunge.
	final int beg = i;
	final long[] deathRow = nBits(end - beg);
	deathRow[0] = 1L; // set bit 0
	for (i = beg + 1; i < end; i++)
	if (filter.test((E) es[i]))
	setBit(deathRow, i - beg);
	if (modCount != expectedModCount)
	throw new ConcurrentModificationException();
	int w = beg;
	for (i = beg; i < end; i++)
	if (isClear(deathRow, i - beg))
	es[w++] = es[i];
	for (i = size = w; i < end; i++)
	es[i] = null;
	heapify();
	return true;
	}

	/**
	* @throws NullPointerException {@inheritDoc}
	*/
	public void forEach(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	final int expectedModCount = modCount;
	final Object[] es = queue;
	for (int i = 0, n = size; i < n; i++)
	action.accept((E) es[i]);
	if (expectedModCount != modCount)
	throw new ConcurrentModificationException();
	}
	}

Back to index...