--- jsr166/src/main/java/util/PriorityQueue.java 2003/08/25 19:27:54 1.31 +++ jsr166/src/main/java/util/PriorityQueue.java 2015/09/20 16:20:21 1.107 @@ -1,84 +1,105 @@ - package java.util; +/* + * 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. - * This queue orders - * elements according to an order specified at construction time, which is - * specified in the same manner as {@link java.util.TreeSet} and - * {@link java.util.TreeMap}: elements are ordered - * either according to their natural order (see {@link Comparable}), or - * according to a {@link java.util.Comparator}, depending on which - * constructor is used. - *

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. A priority queue does not permit - * null elements. - * - *

The {@link #remove()} and {@link #poll()} methods remove and - * return the head of the queue. - * - *

The {@link #element()} and {@link #peek()} methods return, but do - * not delete, the head of the queue. - * - *

A priority queue has a capacity. The capacity is the - * size of the array used internally 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. - * - *

The Iterator provided in method {@link #iterator()} is not - * guaranteed to traverse the elements of the PriorityQueue in any - * particular order. If you need ordered traversal, consider using - * Arrays.sort(pq.toArray()). - * - *

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

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

This class and its iterator implement all of the + * optional methods of the {@link Collection} and {@link + * Iterator} interfaces. The Iterator provided in method {@link + * #iterator()} is not guaranteed to traverse the elements of + * 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 + * @author Josh Bloch, Doug Lea + * @param the type of elements held in this queue */ public class PriorityQueue extends AbstractQueue - implements Queue, java.io.Serializable { + 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] 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[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 transient Object[] queue; + transient Object[] queue; // non-private to simplify nested class access /** * The number of elements in the priority queue. */ - private int size = 0; + int size; /** * The comparator, or null if priority queue uses elements' @@ -90,357 +111,460 @@ public class PriorityQueue extends Ab * The number of times this priority queue has been * structurally modified. See AbstractList for gory details. */ - private transient int modCount = 0; + transient int modCount; // non-private to simplify nested class access /** - * Creates a PriorityQueue with the default initial capacity - * (11) that orders its elements according to their natural - * ordering (using Comparable). + * 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 PriorityQueue with the specified initial capacity - * that orders its elements according to their natural ordering - * (using Comparable). - * - * @param initialCapacity the initial capacity for this priority queue. - * @throws IllegalArgumentException if initialCapacity is less - * than 1 + * 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 PriorityQueue with the specified initial capacity + * Creates a {@code PriorityQueue} with the default initial capacity and + * whose elements are ordered according to the specified comparator. + * + * @param comparator the comparator that will be used to order this + * priority queue. If {@code null}, the {@linkplain Comparable + * natural ordering} of the elements will be used. + * @since 1.8 + */ + public PriorityQueue(Comparator comparator) { + this(DEFAULT_INITIAL_CAPACITY, comparator); + } + + /** + * Creates a {@code PriorityQueue} with the specified initial capacity * that orders its elements according to the specified comparator. * - * @param initialCapacity the initial capacity for this priority queue. - * @param comparator the comparator used to order this priority queue. - * If null then the order depends on the elements' natural - * ordering. - * @throws IllegalArgumentException if initialCapacity is less - * than 1 + * @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, + 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) throw new IllegalArgumentException(); - this.queue = new Object[initialCapacity + 1]; + this.queue = new Object[initialCapacity]; this.comparator = comparator; } /** - * Common code to initialize underlying queue array across - * constructors below. + * 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 */ - private void initializeArray(Collection c) { - int sz = c.size(); - int initialCapacity = (int)Math.min((sz * 110L) / 100, - Integer.MAX_VALUE - 1); - if (initialCapacity < 1) - initialCapacity = 1; - - this.queue = new Object[initialCapacity + 1]; + @SuppressWarnings("unchecked") + 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); + } } /** - * Initially fill elements of the queue array under the - * knowledge that it is sorted or is another PQ, in which - * case we can just place the elements without fixups. + * 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 */ - private void fillFromSorted(Collection c) { - for (Iterator i = c.iterator(); i.hasNext(); ) - queue[++size] = i.next(); + @SuppressWarnings("unchecked") + public PriorityQueue(PriorityQueue c) { + this.comparator = (Comparator) c.comparator(); + initFromPriorityQueue(c); } - /** - * Initially fill elements of the queue array that is - * not to our knowledge sorted, so we must add them - * one by one. + * 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 */ - private void fillFromUnsorted(Collection c) { - for (Iterator i = c.iterator(); i.hasNext(); ) - add(i.next()); + @SuppressWarnings("unchecked") + public PriorityQueue(SortedSet c) { + this.comparator = (Comparator) c.comparator(); + initElementsFromCollection(c); } - /** - * Creates a PriorityQueue containing the elements in the - * specified collection. The priority queue has an initial - * capacity of 110% of the size of the specified collection or 1 - * if the collection is empty. If the specified collection is an - * instance of a {@link java.util.SortedSet} or is another - * PriorityQueue, 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. Otherwise, the priority queue is - * ordered according to its elements' natural order. - * - * @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 c or any element within it - * is null - */ - public PriorityQueue(Collection c) { - initializeArray(c); - if (c instanceof SortedSet) { - // @fixme double-cast workaround for compiler - SortedSet s = (SortedSet) (SortedSet)c; - comparator = (Comparator)s.comparator(); - fillFromSorted(s); - } else if (c instanceof PriorityQueue) { - PriorityQueue s = (PriorityQueue) c; - comparator = (Comparator)s.comparator(); - fillFromSorted(s); + private void initFromPriorityQueue(PriorityQueue c) { + if (c.getClass() == PriorityQueue.class) { + this.queue = c.toArray(); + this.size = c.size(); } else { - comparator = null; - fillFromUnsorted(c); + initFromCollection(c); } } + private void initElementsFromCollection(Collection c) { + Object[] a = c.toArray(); + // If c.toArray incorrectly doesn't return Object[], copy it. + if (a.getClass() != Object[].class) + a = Arrays.copyOf(a, a.length, Object[].class); + 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; + } + /** - * Creates a PriorityQueue containing the elements in the - * specified collection. The priority queue has an initial - * capacity of 110% of the size of the specified collection or 1 - * if the collection is empty. This priority queue will be sorted - * according to the same comparator as the given collection, or - * according to its elements' natural order if the collection is - * sorted according to its elements' natural order. + * Initializes queue array with elements from the given Collection. * - * @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 c or any element within it - * is null + * @param c the collection */ - public PriorityQueue(PriorityQueue c) { - initializeArray(c); - comparator = (Comparator)c.comparator(); - fillFromSorted(c); + private void initFromCollection(Collection c) { + initElementsFromCollection(c); + heapify(); } /** - * Creates a PriorityQueue containing the elements in the - * specified collection. The priority queue has an initial - * capacity of 110% of the size of the specified collection or 1 - * if the collection is empty. This priority queue will be sorted - * according to the same comparator as the given collection, or - * according to its elements' natural order if the collection is - * sorted according to its elements' natural order. - * - * @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 c or any element within it - * is null + * 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 */ - public PriorityQueue(SortedSet c) { - initializeArray(c); - comparator = (Comparator)c.comparator(); - fillFromSorted(c); - } + private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; /** - * Resize array, if necessary, to be able to hold given index + * Increases the capacity of the array. + * + * @param minCapacity the desired minimum capacity */ - private void grow(int index) { - int newlen = queue.length; - if (index < newlen) // don't need to grow - return; - if (index == Integer.MAX_VALUE) - throw new OutOfMemoryError(); - while (newlen <= index) { - if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow - newlen = Integer.MAX_VALUE; - else - newlen <<= 2; - } - Object[] newQueue = new Object[newlen]; - System.arraycopy(queue, 0, newQueue, 0, queue.length); - queue = newQueue; + 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); } - - // Queue Methods + 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); + } /** - * Add the specified element to this priority queue. + * Inserts the specified element into this priority queue. * - * @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. + * @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 o) { - if (o == null) + public boolean offer(E e) { + if (e == null) throw new NullPointerException(); modCount++; - ++size; - - // Grow backing store if necessary - if (size >= queue.length) - grow(size); - - queue[size] = o; - fixUp(size); + int i = size; + if (i >= queue.length) + grow(i + 1); + size = i + 1; + if (i == 0) + queue[0] = e; + else + siftUp(i, e); return true; } - public E poll() { - if (size == 0) - return null; - return (E) remove(1); - } - + @SuppressWarnings("unchecked") public E peek() { - return (E) queue[1]; + return (size == 0) ? null : (E) queue[0]; } - // Collection Methods - the first two override to update docs + private int indexOf(Object o) { + if (o != null) { + for (int i = 0; i < size; i++) + if (o.equals(queue[i])) + return i; + } + return -1; + } /** - * Adds the specified element to this queue. - * @return true (as per the general contract of - * Collection.add). + * 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). * - * @throws NullPointerException {@inheritDoc} - * @throws ClassCastException if the specified element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. + * @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 add(E o) { - return super.add(o); + public boolean remove(Object o) { + int i = indexOf(o); + if (i == -1) + return false; + else { + removeAt(i); + return true; + } } - /** - * Adds all of the elements in the specified collection to this queue. - * The behavior of this operation is undefined if - * the specified collection is modified while the operation is in - * progress. (This implies that the behavior of this call is undefined if - * the specified collection is this queue, and this queue is nonempty.) - *

- * This implementation iterates over the specified collection, and adds - * each object returned by the iterator to this collection, in turn. - * @throws NullPointerException {@inheritDoc} - * @throws ClassCastException if any element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. + * 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 */ - public boolean addAll(Collection c) { - return super.addAll(c); + 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; + } - /** - * Removes a single instance of the specified element from this - * queue, if it is present. More formally, - * removes an element e such that (o==null ? e==null : - * o.equals(e)), if the queue contains one or more such - * elements. Returns true if the queue contained the - * specified element (or equivalently, if the queue changed as a - * result of the call). + /** + * Returns an array containing all of the elements in this queue. + * The elements are in no particular order. * - *

This implementation iterates over the queue looking for the - * specified element. If it finds the element, it removes the element - * from the queue using the iterator's remove method.

+ *

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 boolean remove(Object o) { - if (o == null) - return false; + public Object[] toArray() { + return Arrays.copyOf(queue, size); + } - if (comparator == null) { - for (int i = 1; i <= size; i++) { - if (((Comparable)queue[i]).compareTo((E)o) == 0) { - remove(i); - return true; - } - } - } else { - for (int i = 1; i <= size; i++) { - if (comparator.compare((E)queue[i], (E)o) == 0) { - remove(i); - return true; - } - } - } - return false; + /** + * 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 + */ + @SuppressWarnings("unchecked") + public T[] toArray(T[] a) { + final int size = this.size; + if (a.length < size) + // Make a new array of a's runtime type, but my contents: + return (T[]) Arrays.copyOf(queue, size, a.getClass()); + System.arraycopy(queue, 0, a, 0, size); + 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. + * @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. */ - private int cursor = 1; + private int cursor; /** - * 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. + * 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 = 0; + 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; + + /** + * 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 - * List should have. If this expectation is violated, the iterator + * Queue should have. If this expectation is violated, the iterator * has detected concurrent modification. */ private int expectedModCount = modCount; public boolean hasNext() { - return cursor <= size; + return cursor < size || + (forgetMeNot != null && !forgetMeNot.isEmpty()); } + @SuppressWarnings("unchecked") public E next() { - checkForComodification(); - if (cursor > size) - throw new NoSuchElementException(); - E result = (E) 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() { @@ -448,151 +572,338 @@ public class PriorityQueue extends Ab } /** - * Remove all elements from the priority queue. + * Removes all of the elements from this priority queue. + * The queue will be empty after this call returns. */ public void clear() { modCount++; - - // Null out element references to prevent memory leak - for (int i=1; i<=size; i++) + for (int i = 0; i < size; i++) queue[i] = null; - size = 0; } - /** - * Removes and returns the ith element from queue. Recall - * that queue is one-based, so 1 <= i <= size. - * - * XXX: Could further special-case i==size, but is it worth it? - * XXX: Could special-case i==0, but is it worth it? - */ - private E remove(int i) { - assert i <= size; + @SuppressWarnings("unchecked") + public E poll() { + if (size == 0) + return null; + int s = --size; modCount++; - - E result = (E) queue[i]; - queue[i] = queue[size]; - queue[size--] = null; // Drop extra ref to prevent memory leak - if (i <= size) - fixDown(i); + E result = (E) queue[0]; + E x = (E) queue[s]; + queue[s] = null; + if (s != 0) + siftDown(0, x); return result; } /** - * 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((E)queue[k]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } - } else { - while (k > 1) { - int j = k >> 1; - if (comparator.compare((E)queue[j], (E)queue[k]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; + * 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; } /** - * 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)queue[j]).compareTo((E)queue[j+1]) > 0) - j++; // j indexes smallest kid - if (((Comparable)queue[k]).compareTo((E)queue[j]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } - } else { - while ((j = k << 1) <= size) { - if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0) - j++; // j indexes smallest kid - if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } + * 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 key = (Comparable) 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 key = (Comparable)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) 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. + */ + @SuppressWarnings("unchecked") + private void heapify() { + for (int i = (size >>> 1) - 1; i >= 0; i--) + siftDown(i, (E) queue[i]); + } /** - * Returns the comparator used to order this collection, or null - * if this collection is sorted according to its elements natural ordering - * (using Comparable). + * 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 collection, or null - * if this collection is sorted according to its elements natural ordering. + * @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; } /** - * Save the state of the instance to a stream (that - * is, serialize it). + * Saves this queue to a stream (that is, serializes it). * * @serialData The length of the array backing the instance is - * emitted (int), followed by all of its elements (each an - * Object) in the proper order. + * emitted (int), followed by all of its elements + * (each an {@code Object}) in the proper order. * @param s the stream + * @throws java.io.IOException if an I/O error occurs */ private void writeObject(java.io.ObjectOutputStream s) - throws java.io.IOException{ + throws java.io.IOException { // Write out element count, and any hidden stuff s.defaultWriteObject(); - // Write out array length - s.writeInt(queue.length); + // Write out array length, for compatibility with 1.5 version + s.writeInt(Math.max(2, size + 1)); - // Write out all elements in the proper order. - for (int i=0; iArrayList instance from a stream (that is, - * deserialize it). + * Reconstitutes the {@code PriorityQueue} instance from a stream + * (that is, deserializes it). + * * @param s the stream + * @throws ClassNotFoundException if the class of a serialized object + * could not be found + * @throws java.io.IOException if an I/O error occurs */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in size, and any hidden stuff s.defaultReadObject(); - // Read in array length and allocate array - int arrayLength = s.readInt(); - queue = new Object[arrayLength]; + // Read in (and discard) array length + s.readInt(); + + queue = new Object[size]; - // Read in all elements in the proper order. - for (int i=0; ilate-binding + * and fail-fast {@link Spliterator} over the elements in this + * queue. + * + *

The {@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<>(this, 0, -1, 0); + } + static final class PriorityQueueSpliterator implements Spliterator { + /* + * This is very similar to ArrayList Spliterator, except for + * extra null checks. + */ + private final PriorityQueue pq; + 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(PriorityQueue pq, int origin, int fence, + int expectedModCount) { + this.pq = pq; + 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 = pq.modCount; + hi = fence = pq.size; + } + return hi; + } + + public PriorityQueueSpliterator trySplit() { + int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; + return (lo >= mid) ? null : + new PriorityQueueSpliterator<>(pq, lo, index = mid, + expectedModCount); + } + + @SuppressWarnings("unchecked") + public void forEachRemaining(Consumer action) { + int i, hi, mc; // hoist accesses and checks from loop + PriorityQueue q; Object[] a; + if (action == null) + throw new NullPointerException(); + if ((q = pq) != null && (a = q.queue) != null) { + if ((hi = fence) < 0) { + mc = q.modCount; + hi = q.size; + } + else + mc = expectedModCount; + if ((i = index) >= 0 && (index = hi) <= a.length) { + for (E e;; ++i) { + if (i < hi) { + if ((e = (E) a[i]) == null) // must be CME + break; + action.accept(e); + } + else if (q.modCount != mc) + break; + else + return; + } + } + } + throw new ConcurrentModificationException(); + } + + public boolean tryAdvance(Consumer action) { + if (action == null) + throw new NullPointerException(); + int hi = getFence(), lo = index; + if (lo >= 0 && lo < hi) { + index = lo + 1; + @SuppressWarnings("unchecked") E e = (E)pq.queue[lo]; + if (e == null) + throw new ConcurrentModificationException(); + action.accept(e); + if (pq.modCount != expectedModCount) + throw new ConcurrentModificationException(); + return true; + } + return false; + } + + public long estimateSize() { + return (long) (getFence() - index); + } + + public int characteristics() { + return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL; + } + } +}