--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/PriorityQueue.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,896 @@
+/*
+ * Copyright (c) 2003, 2013, 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;
+
+/**
+ * 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/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
+ */
+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[2*n+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
+ */
+ @SuppressWarnings("unchecked")
+ 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
+ */
+ @SuppressWarnings("unchecked")
+ 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
+ */
+ @SuppressWarnings("unchecked")
+ public PriorityQueue(SortedSet<? extends E> c) {
+ this.comparator = (Comparator<? super E>) c.comparator();
+ initElementsFromCollection(c);
+ }
+
+ private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
+ if (c.getClass() == PriorityQueue.class) {
+ this.queue = c.toArray();
+ this.size = c.size();
+ } else {
+ initFromCollection(c);
+ }
+ }
+
+ private void initElementsFromCollection(Collection<? extends E> 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);
+ 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<? 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;
+ }
+
+ @SuppressWarnings("unchecked")
+ public E peek() {
+ return (size == 0) ? null : (E) queue[0];
+ }
+
+ private int indexOf(Object o) {
+ if (o != null) {
+ for (int i = 0; i < size; i++)
+ if (o.equals(queue[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;
+ }
+ }
+
+ /**
+ * Version of remove using reference equality, not equals.
+ * Needed by iterator.remove.
+ *
+ * @param o element to be removed from this queue, if present
+ * @return {@code true} if removed
+ */
+ boolean removeEq(Object o) {
+ for (int i = 0; i < size; i++) {
+ if (o == queue[i]) {
+ removeAt(i);
+ return true;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * 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
+ */
+ @SuppressWarnings("unchecked")
+ 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());
+ }
+
+ @SuppressWarnings("unchecked")
+ 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++;
+ for (int i = 0; i < size; i++)
+ queue[i] = null;
+ 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];
+ queue[s] = null;
+ if (s != 0)
+ siftDown(0, x);
+ 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.
+ */
+ @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;
+ siftDown(i, moved);
+ if (queue[i] == moved) {
+ siftUp(i, moved);
+ if (queue[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);
+ else
+ siftUpComparable(k, x);
+ }
+
+ @SuppressWarnings("unchecked")
+ private void siftUpComparable(int k, E x) {
+ Comparable<? super E> key = (Comparable<? super E>) x;
+ while (k > 0) {
+ int parent = (k - 1) >>> 1;
+ Object e = queue[parent];
+ if (key.compareTo((E) e) >= 0)
+ break;
+ queue[k] = e;
+ k = parent;
+ }
+ 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)
+ break;
+ queue[k] = e;
+ k = parent;
+ }
+ queue[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);
+ else
+ siftDownComparable(k, x);
+ }
+
+ @SuppressWarnings("unchecked")
+ private void siftDownComparable(int k, E x) {
+ Comparable<? super E> key = (Comparable<? super E>)x;
+ int half = size >>> 1; // loop while a non-leaf
+ while (k < half) {
+ int child = (k << 1) + 1; // assume left child is least
+ Object c = queue[child];
+ int right = child + 1;
+ if (right < size &&
+ ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
+ c = queue[child = right];
+ if (key.compareTo((E) c) <= 0)
+ break;
+ queue[k] = c;
+ k = child;
+ }
+ queue[k] = key;
+ }
+
+ @SuppressWarnings("unchecked")
+ private void siftDownUsingComparator(int k, E x) {
+ int half = size >>> 1;
+ while (k < half) {
+ int child = (k << 1) + 1;
+ 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)
+ break;
+ queue[k] = c;
+ k = child;
+ }
+ queue[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).
+ */
+ @SuppressWarnings("unchecked")
+ private void heapify() {
+ 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 {@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".
+ for (int i = 0; i < size; i++)
+ s.writeObject(queue[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();
+
+ queue = new Object[size];
+
+ // Read in all elements.
+ for (int i = 0; i < size; i++)
+ queue[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);
+ }
+
+ @SuppressWarnings("unchecked")
+ public void forEachRemaining(Consumer<? super E> 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<? 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;
+ }
+ }
+}