--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/19 02:45:07 1.4
+++ jsr166/src/main/java/util/PriorityQueue.java 2019/08/30 18:05:39 1.132
@@ -1,414 +1,973 @@
- package java.util;
-
/*
- * Todo
+ * Copyright (c) 2003, 2019, 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.
*
- * 1) Make it serializable.
+ * 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;
+// OPENJDK import jdk.internal.access.SharedSecrets;
+import jdk.internal.util.ArraysSupport;
+
/**
- * An unbounded priority queue based on a priority heap. This queue orders
- * elements according to the order specified at creation time. This order is
- * specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
- * either according to their natural order (see {@link Comparable}), or
- * according to a {@link Comparator}, depending on which constructor is used.
- * The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
- * minimal element with respect to the specified ordering. If multiple
- * these elements are tied for least value, no guarantees are made as to
- * which of elements is returned.
- *
- * Each priority queue has a capacity. The capacity is the size of
- * the 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 list,
- * its capacity grows automatically. The details of the growth policy are not
+ * 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 {@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
+ * capacity 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.
*
- *
Implementation note: this implementation provides O(log(n)) time for
- * the offer, poll, remove() and add
- * methods; linear time for the remove(Object) and
- * contains methods; and constant time for the peek,
- * element, and size methods.
+ *
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()} 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 {@code Arrays.sort(pq.toArray())}.
+ *
+ *
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 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
+ * @author Josh Bloch, Doug Lea
+ * @param the type of elements held in this queue
*/
+@SuppressWarnings("unchecked")
public class PriorityQueue extends AbstractQueue
- implements Queue
-{
+ implements java.io.Serializable {
+
+ // OPENJDK @java.io.Serial
+ 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] 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
- * of n, d, n <= d.
- *
- * The element with the lowest value is in queue[1] (assuming the queue is
- * nonempty). A one-based array is used in preference to the traditional
- * zero-based array to simplify parent and child calculations.
- *
- * queue.length must be >= 2, even if size == 0.
+ * 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.
*/
- private E[] 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'
* natural ordering.
*/
- private final Comparator comparator;
+ private final Comparator comparator;
/**
* The number of times this priority queue has been
* structurally modified. See AbstractList for gory details.
*/
- private int modCount = 0;
+ transient int modCount; // non-private to simplify nested class access
/**
- * Create a new priority queue with the default initial capacity (11)
- * that orders its elements according to their natural ordering.
+ * 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);
+ this(DEFAULT_INITIAL_CAPACITY, null);
}
/**
- * Create a new priority queue with the specified initial capacity
- * that orders its elements according to their natural ordering.
+ * 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.
+ * @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);
}
/**
- * Create a new priority queue with the specified initial capacity (11)
- * that orders its elements according to the specified comparator.
+ * Creates a {@code PriorityQueue} with the default initial capacity and
+ * whose elements are ordered according to the specified comparator.
*
- * @param initialCapacity the initial capacity for this priority queue.
- * @param comparator the comparator used to order 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.
+ * @since 1.8
*/
- public PriorityQueue(int initialCapacity, Comparator comparator) {
+ 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 {@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 comparator) {
+ // Note: This restriction of at least one is not actually needed,
+ // but continues for 1.5 compatibility
if (initialCapacity < 1)
- initialCapacity = 1;
- queue = new E[initialCapacity + 1];
+ throw new IllegalArgumentException();
+ this.queue = new Object[initialCapacity];
this.comparator = comparator;
}
/**
- * Create a new priority queue containing the elements in the specified
- * collection. The priority queue has an initial capacity of 110% of the
- * size of the specified collection. If the specified collection
- * implements the {@link Sorted} interface, the priority queue will be
- * sorted according to the same comparator, or according to its elements'
- * natural order if the collection is sorted according to its elements'
- * natural order. If the specified collection does not implement the
- * Sorted interface, the priority queue is ordered according to
- * its elements' natural order.
+ * 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 initialElements the collection whose elements are to be placed
- * into this priority queue.
+ * @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 an
- * element of the specified collection is null.
- */
- public PriorityQueue(Collection initialElements) {
- int sz = initialElements.size();
- int initialCapacity = (int)Math.min((sz * 110L) / 100,
- Integer.MAX_VALUE - 1);
- if (initialCapacity < 1)
- initialCapacity = 1;
- queue = new E[initialCapacity + 1];
+ * queue's ordering
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
+ */
+ public PriorityQueue(Collection c) {
+ 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 {
+ this.comparator = null;
+ initFromCollection(c);
+ }
+ }
- if (initialElements instanceof Sorted) {
- comparator = ((Sorted)initialElements).comparator();
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- queue[++size] = i.next();
+ /**
+ * 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 c) {
+ this.comparator = (Comparator) 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 c) {
+ this.comparator = (Comparator) 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 c) {
+ if (c.getClass() == PriorityQueue.class) {
+ this.queue = ensureNonEmpty(c.toArray());
+ this.size = c.size();
} else {
- comparator = null;
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- add(i.next());
+ initFromCollection(c);
}
}
- // Queue Methods
+ private void initElementsFromCollection(Collection 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;
+ }
/**
- * Remove and return the minimal element from this priority queue if
- * it contains one or more elements, otherwise null. The term
- * minimal is defined according to this priority queue's order.
+ * Initializes queue array with elements from the given Collection.
*
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
+ * @param c the collection
*/
- public E poll() {
- if (size == 0)
- return null;
- return remove(1);
+ private void initFromCollection(Collection c) {
+ initElementsFromCollection(c);
+ heapify();
+ }
+
+ /**
+ * 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 = ArraysSupport.newLength(oldCapacity,
+ minCapacity - oldCapacity, /* minimum growth */
+ oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1
+ /* preferred growth */);
+ queue = Arrays.copyOf(queue, newCapacity);
+ }
+
+ /**
+ * 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);
}
/**
- * Return, but do not remove, the minimal element from the priority queue,
- * or null if the queue is empty. The term minimal is
- * defined according to this priority queue's order. This method returns
- * the same object reference that would be returned by by the
- * poll method. The two methods differ in that this method
- * does not remove the element from the priority queue.
+ * Inserts the specified element into this priority queue.
*
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
+ * @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 queue[1];
+ return (E) queue[0];
}
- // Collection Methods
+ 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 priority
- * queue, if it is present. Returns true if this collection contained the
- * specified element (or equivalently, if this collection changed as a
+ * 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 collection, if present.
- * @return true if this collection changed as a result of the
- * call
- * @throws ClassCastException if the specified element cannot be compared
- * with elements currently in the priority queue according
- * to the priority queue's ordering.
- * @throws NullPointerException if the specified element is null.
+ * @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 element) {
- if (element == null)
- throw new NullPointerException();
+ public boolean remove(Object o) {
+ int i = indexOf(o);
+ if (i == -1)
+ return false;
+ else {
+ removeAt(i);
+ return true;
+ }
+ }
- if (comparator == null) {
- for (int i = 1; i <= size; i++) {
- if (((Comparable)queue[i]).compareTo(element) == 0) {
- remove(i);
- return true;
- }
- }
- } else {
- for (int i = 1; i <= size; i++) {
- if (comparator.compare(queue[i], (E) element) == 0) {
- remove(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;
}
}
- return false;
}
/**
- * Returns an iterator over the elements in this priority queue. The
- * first element returned by this iterator is the same element that
- * would be returned by a call to peek.
+ * 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)}.
*
- * @return an Iterator over the elements in this priority queue.
+ * @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.
+ *
+ * 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.
+ *
+ *
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.
+ *
+ *
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}.
+ *
+ *
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 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[] 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 iterator() {
return new Itr();
}
- private class Itr implements Iterator {
+ private final class Itr implements Iterator {
/**
* Index (into queue array) of element to be returned by
* subsequent call to next.
*/
- int cursor = 1;
+ 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 forgetMeNot;
/**
- * Index of element returned by most recent call to next or
- * previous. Reset to 0 if this element is deleted by a call
- * to remove.
+ * Element returned by the most recent call to next iff that
+ * element was drawn from the forgetMeNot list.
*/
- int lastRet = 0;
+ 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.
*/
- int expectedModCount = modCount;
+ private int expectedModCount = modCount;
+
+ Itr() {} // prevent access constructor creation
public boolean hasNext() {
- return cursor <= size;
+ return cursor < size ||
+ (forgetMeNot != null && !forgetMeNot.isEmpty());
}
public E next() {
- checkForComodification();
- if (cursor > size)
- throw new NoSuchElementException();
- E result = queue[cursor];
- lastRet = cursor++;
- return result;
+ 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 (lastRet == 0)
+ 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();
- checkForComodification();
-
- PriorityQueue.this.remove(lastRet);
- if (lastRet < cursor)
- cursor--;
- lastRet = 0;
+ }
expectedModCount = modCount;
}
+ }
- final void checkForComodification() {
- if (modCount != expectedModCount)
- throw new ConcurrentModificationException();
+ 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 cmp;
+ if ((cmp = comparator) == null)
+ siftDownComparable(0, x, es, n);
+ else
+ siftDownUsingComparator(0, x, es, n, cmp);
+ }
}
+ return result;
}
/**
- * Returns the number of elements in this priority queue.
+ * Removes the ith element from queue.
*
- * @return the number of elements in this priority queue.
- */
- public int size() {
- return size;
+ * 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;
}
/**
- * Add the specified element to this priority queue.
+ * 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.
*
- * @param element the element to add.
- * @return true
- * @throws ClassCastException if the specified element cannot be compared
- * with elements currently in the priority queue according
- * to the priority queue's ordering.
- * @throws NullPointerException if the specified element is null.
+ * 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
*/
- public boolean offer(E element) {
- if (element == null)
- throw new NullPointerException();
- modCount++;
+ private void siftUp(int k, E x) {
+ if (comparator != null)
+ siftUpUsingComparator(k, x, queue, comparator);
+ else
+ siftUpComparable(k, x, queue);
+ }
- // Grow backing store if necessary
- if (++size == queue.length) {
- E[] newQueue = new E[2 * queue.length];
- System.arraycopy(queue, 0, newQueue, 0, size);
- queue = newQueue;
+ private static void siftUpComparable(int k, T x, Object[] es) {
+ Comparable key = (Comparable) 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;
+ }
- queue[size] = element;
- fixUp(size);
- return true;
+ private static void siftUpUsingComparator(
+ int k, T x, Object[] es, Comparator 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 void siftDownComparable(int k, T x, Object[] es, int n) {
+ // assert n > 0;
+ Comparable key = (Comparable)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) 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 void siftDownUsingComparator(
+ int k, T x, Object[] es, int n, Comparator 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;
}
/**
- * Remove all elements from the priority queue.
+ * 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).
*/
- public void clear() {
- modCount++;
+ private void heapify() {
+ final Object[] es = queue;
+ int n = size, i = (n >>> 1) - 1;
+ final Comparator 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 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.
+ */
+ // OPENJDK @java.io.Serial
+ private void writeObject(java.io.ObjectOutputStream s)
+ throws java.io.IOException {
+ // Write out element count, and any hidden stuff
+ s.defaultWriteObject();
- // Null out element references to prevent memory leak
- for (int i=1; i<=size; i++)
- queue[i] = null;
+ // Write out array length, for compatibility with 1.5 version
+ s.writeInt(Math.max(2, size + 1));
- size = 0;
+ // 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]);
}
/**
- * Removes and returns the ith element from queue. Recall
- * that queue is one-based, so 1 <= i <= size.
+ * Reconstitutes the {@code PriorityQueue} instance from a stream
+ * (that is, deserializes it).
*
- * XXX: Could further special-case i==size, but is it worth it?
- * XXX: Could special-case i==0, but is it worth 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 E remove(int i) {
- assert i <= size;
- modCount++;
+ // OPENJDK @java.io.Serial
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ // Read in size, and any hidden stuff
+ s.defaultReadObject();
- E result = queue[i];
- queue[i] = queue[size];
- queue[size--] = null; // Drop extra ref to prevent memory leak
- if (i <= size)
- fixDown(i);
- return result;
+ // Read in (and discard) array length
+ s.readInt();
+
+ jsr166.Platform.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();
}
/**
- * Establishes the heap invariant (described above) assuming the heap
- * satisfies the invariant except possibly for the leaf-node indexed by k
- * (which may have a nextExecutionTime less than its parent's).
- *
- * This method functions by "promoting" queue[k] up the hierarchy
- * (by swapping it with its parent) repeatedly until queue[k]
- * is greater than or equal to its parent.
- */
- private void fixUp(int k) {
- if (comparator == null) {
- while (k > 1) {
- int j = k >> 1;
- if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
+ * Creates a late-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;
}
- } else {
- while (k > 1) {
- int j = k >> 1;
- if (comparator.compare(queue[j], queue[k]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
+ 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 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 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;
}
}
/**
- * Establishes the heap invariant (described above) in the subtree
- * rooted at k, which is assumed to satisfy the heap invariant except
- * possibly for node k itself (which may be greater than its children).
- *
- * This method functions by "demoting" queue[k] down the hierarchy
- * (by swapping it with its smaller child) repeatedly until queue[k]
- * is less than or equal to its children.
- */
- private void fixDown(int k) {
- int j;
- if (comparator == null) {
- while ((j = k << 1) <= size) {
- if (j 0)
- j++; // j indexes smallest kid
- if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
- }
- } else {
- while ((j = k << 1) <= size) {
- if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
- j++; // j indexes smallest kid
- if (comparator.compare(queue[k], queue[j]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
- }
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean removeIf(Predicate 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 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;
}
/**
- * Returns the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
- *
- * @return the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
+ * @throws NullPointerException {@inheritDoc}
*/
- Comparator comparator() {
- return comparator;
+ public void forEach(Consumer 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();
}
}