--- jsr166/src/main/java/util/PriorityQueue.java 2003/08/05 12:11:08 1.22
+++ jsr166/src/main/java/util/PriorityQueue.java 2006/03/07 07:11:39 1.63
@@ -1,62 +1,79 @@
- package java.util;
+/*
+ * %W% %E%
+ *
+ * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
+ * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
+ */
+
+package java.util;
/**
- * An unbounded priority 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.
+ * 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 {@link #remove()} and {@link #poll()} methods remove and
- * return the head of the queue.
+ *
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.
*
- *
The {@link #element()} and {@link #peek()} methods return, but do
- * not delete, 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.
*
- *
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.
+ *
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())}.
*
- *
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).
+ *
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 enqueing and dequeing 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
+ * @version %I%, %G%
+ * @author Josh Bloch, Doug Lea
+ * @param the type of elements held in this collection
*/
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;
@@ -78,434 +95,589 @@ public class PriorityQueue extends Ab
private transient int modCount = 0;
/**
- * 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.
+ * 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 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
- */
- public PriorityQueue(int initialCapacity, Comparator 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)
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.
- */
- 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];
- }
-
- /**
- * 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.
- */
- private void fillFromSorted(Collection c) {
- for (Iterator i = c.iterator(); i.hasNext(); )
- queue[++size] = i.next();
- }
-
-
- /**
- * Initially fill elements of the queue array that is
- * not to our knowledge sorted, so we must add them
- * one by one.
- */
- private void fillFromUnsorted(Collection c) {
- for (Iterator i = c.iterator(); i.hasNext(); )
- add(i.next());
- }
-
- /**
- * 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 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.
+ * 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.
+ * @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
+ * queue's ordering
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
*/
public PriorityQueue(Collection c) {
- initializeArray(c);
- if (c instanceof SortedSet) {
- SortedSet s = (SortedSet) c;
- comparator = (Comparator)s.comparator();
- fillFromSorted(s);
- }
- else if (c instanceof PriorityQueue) {
- PriorityQueue s = (PriorityQueue) c;
- comparator = (Comparator)s.comparator();
- fillFromSorted(s);
- }
+ initFromCollection(c);
+ if (c instanceof SortedSet)
+ comparator = (Comparator)
+ ((SortedSet)c).comparator();
+ else if (c instanceof PriorityQueue)
+ comparator = (Comparator)
+ ((PriorityQueue)c).comparator();
else {
comparator = null;
- fillFromUnsorted(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.
+ * 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 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 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) {
- initializeArray(c);
comparator = (Comparator)c.comparator();
- fillFromSorted(c);
+ initFromCollection(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. 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.
+ * 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 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 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) {
- initializeArray(c);
comparator = (Comparator)c.comparator();
- fillFromSorted(c);
+ initFromCollection(c);
}
/**
- * Resize array, if necessary, to be able to hold given index
+ * Initializes queue array with elements from the given Collection.
+ *
+ * @param c the collection
*/
- private void grow(int index) {
- int newlen = queue.length;
- if (index < newlen) // don't need to grow
- return;
- if (index == Integer.MAX_VALUE)
+ private void initFromCollection(Collection c) {
+ Object[] a = c.toArray();
+ // If c.toArray incorrectly doesn't return Object[], copy it.
+ if (a.getClass() != Object[].class)
+ a = Arrays.copyOf(a, a.length, Object[].class);
+ queue = a;
+ size = a.length;
+ }
+
+ /**
+ * Increases the capacity of the array.
+ *
+ * @param minCapacity the desired minimum capacity
+ */
+ private void grow(int minCapacity) {
+ if (minCapacity < 0) // overflow
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;
- }
-
- // Queue Methods
-
- /**
- * Add the specified element to 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.
+ int oldCapacity = queue.length;
+ // Double size if small; else grow by 50%
+ int newCapacity = ((oldCapacity < 64)?
+ ((oldCapacity + 1) * 2):
+ ((oldCapacity / 2) * 3));
+ if (newCapacity < 0) // overflow
+ newCapacity = Integer.MAX_VALUE;
+ if (newCapacity < minCapacity)
+ newCapacity = minCapacity;
+ 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 offer(E o) {
- if (o == 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++;
- ++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() {
+ public E peek() {
if (size == 0)
return null;
- return (E) remove(1);
+ return (E) queue[0];
}
- public E peek() {
- return (E) queue[1];
+ private int indexOf(Object o) {
+ if (o != null) {
+ for (int i = 0; i < size; i++)
+ if (o.equals(queue[i]))
+ return i;
+ }
+ return -1;
}
- // Collection Methods
+ /**
+ * 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;
+ }
+ }
- // these first two override just to get the throws docs
+ /**
+ * 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;
+ }
/**
- * @throws NullPointerException if the specified element is null.
- * @throws ClassCastException if the specified element cannot be compared
- * with elements currently in the priority queue according
- * to the priority queue's ordering.
+ * 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 add(E o) {
- return super.add(o);
+ public boolean contains(Object o) {
+ return indexOf(o) != -1;
}
/**
- * @throws ClassCastException if any element cannot be compared
- * with elements currently in the priority queue according
- * to the priority queue's ordering.
- * @throws NullPointerException if c or any element in c
- * is null
+ * 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 boolean addAll(Collection c) {
- return super.addAll(c);
+ public Object[] toArray() {
+ return Arrays.copyOf(queue, size);
}
- public boolean remove(Object o) {
- if (o == null)
- return false;
-
- 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 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 String:
+ *
+ *
+ * String[] y = x.toArray(new String[0]);
+ *
+ * Note that toArray(new Object[0]) is identical in function to
+ * 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) {
+ 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.
*/
- private int cursor = 1;
+ private int cursor = 0;
/**
- * 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 = null;
+
+ /**
+ * Element returned by the most recent call to next iff that
+ * element was drawn from the forgetMeNot list.
+ */
+ private E lastRetElt = null;
/**
* 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());
}
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();
- }
}
- /**
- * Returns the number of elements in this priority queue.
- *
- * @return the number of elements in this priority queue.
- */
public int size() {
return size;
}
/**
- * 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;
}
+ 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 and returns the ith element from queue. Recall
- * that queue is one-based, so 1 <= i <= size.
+ * Removes the ith element from queue.
*
- * XXX: Could further special-case i==size, but is it worth it?
- * XXX: Could special-case i==0, but is it worth it?
+ * 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.
*/
- private E remove(int i) {
- assert i <= size;
+ private E removeAt(int i) {
+ assert i >= 0 && i < 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);
- return result;
+ 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) 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;
- }
+ * 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);
+ }
+
+ 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;
+ }
+
+ 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;
}
/**
- * 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
+ * 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);
+ }
+
+ 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;
+ }
+
+ 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.
+ */
+ private void heapify() {
+ for (int i = (size >>> 1) - 1; i >= 0; i--)
+ siftDown(i, (E) queue[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 comparator() {
return comparator;
}
/**
- * Save the state of the instance to a stream (that
- * is, serialize it).
+ * Saves the state of the instance 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
*/
private void writeObject(java.io.ObjectOutputStream s)
@@ -513,17 +685,18 @@ public class PriorityQueue extends Ab
// 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
*/
private void readObject(java.io.ObjectInputStream s)
@@ -531,14 +704,13 @@ public class PriorityQueue extends Ab
// 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; i