--- jsr166/src/main/java/util/PriorityQueue.java 2005/11/23 05:33:25 1.53
+++ jsr166/src/main/java/util/PriorityQueue.java 2010/05/10 20:11:01 1.70
@@ -1,28 +1,45 @@
/*
- * @(#)PriorityQueue.java 1.8 05/08/27
+ * Copyright 2003-2006 Sun Microsystems, Inc. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
- * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
- * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
+ * 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. Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
*/
package java.util;
-import java.util.*; // for javadoc (till 6280605 is fixed)
/**
- * 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
- * null elements. A priority queue relying on natural
- * ordering also does not permit insertion of non-comparable objects
- * (doing so may result in ClassCastException).
+ * 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 poll,
- * remove, peek, and element access the
+ * 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
@@ -37,27 +54,27 @@ import java.util.*; // for javadoc (till
* 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 Arrays.sort(pq.toArray()).
+ * traversal, consider using {@code 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
+ * 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 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).
+ *
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
- * @version 1.8, 08/27/05
- * @author Josh Bloch
+ * @author Josh Bloch, Doug Lea
* @param the type of elements held in this collection
*/
public class PriorityQueue extends AbstractQueue
@@ -68,17 +85,12 @@ public class PriorityQueue extends Ab
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;
@@ -100,7 +112,7 @@ public class PriorityQueue extends Ab
private transient int modCount = 0;
/**
- * Creates a PriorityQueue with the default initial
+ * Creates a {@code PriorityQueue} with the default initial
* capacity (11) that orders its elements according to their
* {@linkplain Comparable natural ordering}.
*/
@@ -109,89 +121,46 @@ public class PriorityQueue extends Ab
}
/**
- * Creates a PriorityQueue with the specified initial
+ * 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 initialCapacity is less
- * than 1
+ * @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 that will be used to order
- * this priority queue. If null, the natural
- * ordering of the elements will be used.
- * @throws IllegalArgumentException if initialCapacity is
+ * @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 in the order presented.
- */
- private void fillFromSorted(Collection c) {
- for (Iterator i = c.iterator(); i.hasNext(); ) {
- int k = ++size;
- if (k >= queue.length)
- grow(k);
- queue[k] = i.next();
- }
- }
-
- /**
- * Initially fill elements of the queue array that is not to our knowledge
- * sorted, so we must rearrange the elements to guarantee the heap
- * invariant.
- */
- private void fillFromUnsorted(Collection c) {
- for (Iterator i = c.iterator(); i.hasNext(); ) {
- int k = ++size;
- if (k >= queue.length)
- grow(k);
- queue[k] = i.next();
- }
- 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. If the specified collection is an
- * instance of a {@link java.util.SortedSet} or is another
- * PriorityQueue, the priority queue will be ordered
- * according to the same ordering. Otherwise, this priority queue
- * will be ordered according to the natural ordering of its elements.
+ * 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
@@ -201,87 +170,133 @@ public class PriorityQueue extends Ab
* @throws NullPointerException if the specified collection or any
* of its elements are null
*/
+ @SuppressWarnings("unchecked")
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);
- } else {
- comparator = null;
- fillFromUnsorted(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);
}
}
/**
- * Creates a PriorityQueue containing the elements in the
- * specified priority queue. The priority queue has an initial
- * capacity of 110% of the size of the specified priority queue or
- * 1 if the priority queue is empty. This priority queue will be
+ * 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 c cannot be
- * compared to one another according to c's
+ * @throws ClassCastException if elements of {@code c} cannot be
+ * compared to one another according to {@code c}'s
* ordering
* @throws NullPointerException if the specified priority queue or any
* of its elements are null
*/
+ @SuppressWarnings("unchecked")
public PriorityQueue(PriorityQueue c) {
- initializeArray(c);
- comparator = (Comparator)c.comparator();
- fillFromSorted(c);
+ this.comparator = (Comparator) c.comparator();
+ initFromPriorityQueue(c);
}
/**
- * Creates a PriorityQueue containing the elements in the
- * specified sorted set. The priority queue has an initial
- * capacity of 110% of the size of the specified sorted set or 1
- * if the sorted set is empty. This priority queue will be ordered
+ * 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.
+ * into this priority queue
* @throws ClassCastException if elements of the specified sorted
* set cannot be compared to one another according to the
* sorted set's ordering
* @throws NullPointerException if the specified sorted set or any
* of its elements are null
*/
+ @SuppressWarnings("unchecked")
public PriorityQueue(SortedSet c) {
- initializeArray(c);
- comparator = (Comparator)c.comparator();
- fillFromSorted(c);
+ this.comparator = (Comparator) c.comparator();
+ initElementsFromCollection(c);
}
+ private void initFromPriorityQueue(PriorityQueue c) {
+ if (c.getClass() == PriorityQueue.class) {
+ this.queue = c.toArray();
+ this.size = c.size();
+ } else {
+ 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 (int i = 0; i < len; i++)
+ if (a[i] == null)
+ throw new NullPointerException();
+ this.queue = a;
+ this.size = a.length;
+ }
+
+ /**
+ * Initializes queue array with elements from the given Collection.
+ *
+ * @param c the collection
+ */
+ private void initFromCollection(Collection c) {
+ initElementsFromCollection(c);
+ heapify();
+ }
+
+ /**
+ * The maximum size of array to allocate.
+ * Some VMs reserve some header words in an array.
+ * Attempts to allocate larger arrays may result in
+ * OutOfMemoryError: Requested array size exceeds VM limit
+ */
+ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
+
/**
- * 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)
+ private void grow(int minCapacity) {
+ int oldCapacity = queue.length;
+ // Double size if small; else grow by 50%
+ int newCapacity = oldCapacity + ((oldCapacity < 64) ?
+ (oldCapacity + 2) :
+ (oldCapacity >> 1));
+ // overflow-conscious code
+ if (newCapacity - MAX_ARRAY_SIZE > 0)
+ newCapacity = hugeCapacity(minCapacity);
+ queue = Arrays.copyOf(queue, newCapacity);
+ }
+
+ private static int hugeCapacity(int minCapacity) {
+ if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
- while (newlen <= index) {
- if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow
- newlen = Integer.MAX_VALUE;
- else
- newlen <<= 2;
- }
- queue = Arrays.copyOf(queue, newlen);
+ return (minCapacity > MAX_ARRAY_SIZE) ?
+ Integer.MAX_VALUE :
+ MAX_ARRAY_SIZE;
}
/**
* Inserts the specified element into this priority queue.
*
- * @return true (as specified by {@link Collection#add})
+ * @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
@@ -294,7 +309,7 @@ public class PriorityQueue extends Ab
/**
* Inserts the specified element into this priority queue.
*
- * @return true (as specified by {@link Queue#offer})
+ * @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
@@ -304,97 +319,131 @@ public class PriorityQueue extends Ab
if (e == null)
throw new NullPointerException();
modCount++;
- ++size;
-
- // Grow backing store if necessary
- if (size >= queue.length)
- grow(size);
-
- queue[size] = e;
- 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 peek() {
if (size == 0)
return null;
- return (E) queue[1];
+ return (E) queue[0];
}
private int indexOf(Object o) {
- if (o == null)
- return -1;
- for (int i = 1; i <= size; i++)
- if (o.equals(queue[i]))
- return i;
+ if (o != null) {
+ for (int i = 0; i < size; i++)
+ if (o.equals(queue[i]))
+ return i;
+ }
return -1;
}
/**
* Removes a single instance of the specified element from this queue,
- * if it is present. More formally, removes an element e such
- * that o.equals(e), if this queue contains one or more such
- * elements. Returns true if this queue contained the specified element
- * (or equivalently, if this queue changed as a result of the call).
+ * 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 true if this queue changed as a result of the call
+ * @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;
- }
+ int i = indexOf(o);
+ if (i == -1)
+ return false;
+ else {
+ removeAt(i);
+ return true;
+ }
+ }
+
+ /**
+ * Version of remove using reference equality, not equals.
+ * Needed by iterator.remove.
+ *
+ * @param o element to be removed from this queue, if present
+ * @return {@code true} if removed
+ */
+ boolean removeEq(Object o) {
+ for (int i = 0; i < size; i++) {
+ if (o == queue[i]) {
+ removeAt(i);
+ return true;
+ }
+ }
+ return false;
}
/**
- * Returns true if this queue contains the specified element.
- * More formally, returns true if and only if this queue contains
- * at least one element e such that o.equals(e).
+ * 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 true if this queue contains the specified element
+ * @return {@code true} if this queue contains the specified element
*/
public boolean contains(Object o) {
- return indexOf(o) != -1;
+ return indexOf(o) != -1;
}
/**
- * Returns an array containing all of the elements in this queue,
+ * 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 list. (In other words, this method must allocate
+ * maintained by this queue. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
- * @return an array containing all of the elements in this queue.
+ *
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.copyOfRange(queue, 1, size+1);
+ return Arrays.copyOf(queue, size);
}
/**
- * Returns an array containing all of the elements in this queue.
- * The elements are in no particular order. The runtime type of
- * the returned array is that of the specified array. 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.
+ * 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
- * null. (This is useful in determining the length of the
- * queue only if the caller knows that the queue does not contain
- * any null elements.)
+ * {@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 the elements of the queue
+ * @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
@@ -403,8 +452,8 @@ public class PriorityQueue extends Ab
public T[] toArray(T[] a) {
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
- return (T[]) Arrays.copyOfRange(queue, 1, size+1, a.getClass());
- System.arraycopy(queue, 1, a, 0, size);
+ return (T[]) Arrays.copyOf(queue, size, a.getClass());
+ System.arraycopy(queue, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
@@ -420,98 +469,86 @@ public class PriorityQueue extends Ab
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,
* unless that element came from the forgetMeNot list.
- * Reset to 0 if element is deleted by a call to remove.
+ * Set to -1 if element is deleted by a call to remove.
*/
- private int lastRet = 0;
+ private int lastRet = -1;
/**
- * The modCount value that the iterator believes that the backing
- * List should have. If this expectation is violated, the iterator
- * has detected concurrent modification.
- */
- private int expectedModCount = modCount;
-
- /**
- * A list of elements that were moved from the unvisited portion of
+ * 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 fixup instead of a fixdown.) We must visit all of
+ * 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 use need to store elements in this field.
+ * will not need to store elements in this field.
*/
- private ArrayList forgetMeNot = null;
+ private ArrayDeque forgetMeNot = null;
/**
* Element returned by the most recent call to next iff that
* element was drawn from the forgetMeNot list.
*/
- private Object lastRetElt = null;
+ private E lastRetElt = null;
+
+ /**
+ * The modCount value that the iterator believes that the backing
+ * Queue should have. If this expectation is violated, the iterator
+ * has detected concurrent modification.
+ */
+ private int expectedModCount = modCount;
public boolean hasNext() {
- return cursor <= size || forgetMeNot != null;
+ return cursor < size ||
+ (forgetMeNot != null && !forgetMeNot.isEmpty());
}
public E next() {
- checkForComodification();
- E result;
- if (cursor <= size) {
- result = (E) queue[cursor];
- lastRet = cursor++;
- }
- else if (forgetMeNot == null)
- throw new NoSuchElementException();
- else {
- int remaining = forgetMeNot.size();
- result = forgetMeNot.remove(remaining - 1);
- if (remaining == 1)
- forgetMeNot = null;
- lastRet = 0;
- lastRetElt = 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;
}
- return result;
+ throw new NoSuchElementException();
}
public void remove() {
- checkForComodification();
-
- if (lastRet != 0) {
+ if (expectedModCount != modCount)
+ throw new ConcurrentModificationException();
+ if (lastRet != -1) {
E moved = PriorityQueue.this.removeAt(lastRet);
- lastRet = 0;
- if (moved == null) {
+ lastRet = -1;
+ if (moved == null)
cursor--;
- } else {
+ else {
if (forgetMeNot == null)
- forgetMeNot = new ArrayList();
+ forgetMeNot = new ArrayDeque();
forgetMeNot.add(moved);
}
} else if (lastRetElt != null) {
- PriorityQueue.this.remove(lastRetElt);
+ PriorityQueue.this.removeEq(lastRetElt);
lastRetElt = null;
} else {
throw new IllegalStateException();
}
-
expectedModCount = modCount;
}
-
- final void checkForComodification() {
- if (modCount != expectedModCount)
- throw new ConcurrentModificationException();
- }
}
public int size() {
@@ -524,52 +561,48 @@ public class PriorityQueue extends Ab
*/
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[1];
- queue[1] = queue[size];
- queue[size--] = null; // Drop extra ref to prevent memory leak
- if (size > 1)
- fixDown(1);
-
+ 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.
*
- * Normally this method leaves the elements at positions from 1 up to i-1,
- * inclusive, untouched. Under these circumstances, it returns null.
- * Occasionally, in order to maintain the heap invariant, it must move
- * the last element of the list to some index in the range [2, i-1],
- * and move the element previously at position (i/2) to position i.
- * Under these circumstances, this method returns the element that was
- * previously at the end of the list and is now at some position between
- * 2 and i-1 inclusive.
+ * 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 removeAt(int i) {
- assert i > 0 && i <= size;
+ assert i >= 0 && i < size;
modCount++;
-
- E moved = (E) queue[size];
- queue[i] = moved;
- queue[size--] = null; // Drop extra ref to prevent memory leak
- if (i <= size) {
- fixDown(i);
+ 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) {
- fixUp(i);
+ siftUp(i, moved);
if (queue[i] != moved)
return moved;
}
@@ -578,67 +611,97 @@ public class PriorityQueue extends Ab
}
/**
- * 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;
- }
- }
- }
-
- /**
- * 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 && (j > 0)) {
- 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 && (j > 0)) {
- if (j 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);
+ }
+
+ 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;
+ }
+
+ /**
+ * 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;
}
/**
@@ -646,30 +709,30 @@ public class PriorityQueue extends Ab
* assuming nothing about the order of the elements prior to the call.
*/
private void heapify() {
- for (int i = size/2; i >= 1; i--)
- fixDown(i);
+ 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 null if this queue is sorted according to
+ * 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
- * null if this queue is sorted according to the
- * natural ordering of its elements.
+ * {@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)
@@ -677,17 +740,18 @@ 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=1; i<=size; i++)
+ // Write out all elements in the "proper order".
+ for (int i = 0; i < size; i++)
s.writeObject(queue[i]);
}
/**
- * Reconstitute the PriorityQueue 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)
@@ -695,13 +759,17 @@ 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 all elements in the proper order.
- for (int i=1; i<=size; i++)
- queue[i] = (E) s.readObject();
- }
+ // Read in (and discard) array length
+ s.readInt();
+
+ queue = new Object[size];
+ // Read in all elements.
+ for (int i = 0; i < size; i++)
+ queue[i] = s.readObject();
+
+ // Elements are guaranteed to be in "proper order", but the
+ // spec has never explained what that might be.
+ heapify();
+ }
}