--- jsr166/src/main/java/util/PriorityQueue.java 2005/11/22 11:44:47 1.52
+++ jsr166/src/main/java/util/PriorityQueue.java 2006/02/16 08:17:21 1.62
@@ -1,12 +1,11 @@
/*
- * @(#)PriorityQueue.java 1.8 05/08/27
+ * %W% %E%
*
- * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
+ * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util;
-import java.util.*; // for javadoc (till 6280605 is fixed)
/**
* An unbounded priority {@linkplain Queue queue} based on a priority
@@ -56,7 +55,7 @@ import java.util.*; // for javadoc (till
*
* Java Collections Framework.
* @since 1.5
- * @version 1.8, 08/27/05
+ * @version %I%, %G%
* @author Josh Bloch
* @param the type of elements held in this collection
*/
@@ -68,17 +67,12 @@ 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;
@@ -134,60 +128,17 @@ public class PriorityQueue extends Ab
*/
public PriorityQueue(int initialCapacity,
Comparator super E> comparator) {
+ // Note: This restriction of at least one is not actually needed,
+ // but continues for 1.5 compatibility
if (initialCapacity < 1)
throw new IllegalArgumentException();
- this.queue = new Object[initialCapacity + 1];
+ this.queue = new Object[initialCapacity];
this.comparator = comparator;
}
/**
- * Common code to initialize underlying queue array across
- * constructors below.
- */
- private void initializeArray(Collection extends E> 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 extends E> c) {
- for (Iterator extends E> 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 extends E> c) {
- for (Iterator extends E> 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
+ * specified collection. 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
@@ -202,26 +153,22 @@ public class PriorityQueue extends Ab
* of its elements are null
*/
public PriorityQueue(Collection extends E> c) {
- initializeArray(c);
- if (c instanceof SortedSet) {
- SortedSet extends E> s = (SortedSet extends E>)c;
- comparator = (Comparator super E>)s.comparator();
- fillFromSorted(s);
- } else if (c instanceof PriorityQueue) {
- PriorityQueue extends E> s = (PriorityQueue extends E>) c;
- comparator = (Comparator super E>)s.comparator();
- fillFromSorted(s);
- } else {
+ initFromCollection(c);
+ if (c instanceof SortedSet)
+ comparator = (Comparator super E>)
+ ((SortedSet extends E>)c).comparator();
+ else if (c instanceof PriorityQueue)
+ comparator = (Comparator super E>)
+ ((PriorityQueue extends E>)c).comparator();
+ else {
comparator = null;
- fillFromUnsorted(c);
+ heapify();
}
}
/**
* 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
+ * specified priority queue. This priority queue will be
* ordered according to the same ordering as the given priority
* queue.
*
@@ -234,16 +181,13 @@ public class PriorityQueue extends Ab
* of its elements are null
*/
public PriorityQueue(PriorityQueue extends E> c) {
- initializeArray(c);
comparator = (Comparator super E>)c.comparator();
- fillFromSorted(c);
+ initFromCollection(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
+ * 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
@@ -255,27 +199,41 @@ public class PriorityQueue extends Ab
* of its elements are null
*/
public PriorityQueue(SortedSet extends E> c) {
- initializeArray(c);
comparator = (Comparator super E>)c.comparator();
- fillFromSorted(c);
+ initFromCollection(c);
}
/**
- * Resize array, if necessary, to be able to hold given index.
+ * Initialize 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 extends E> c) {
+ Object[] a = c.toArray();
+ // If c.toArray incorrectly doesn't return Object[], copy it.
+ if (a.getClass() != Object[].class)
+ a = Arrays.copyOf(a, a.length, Object[].class);
+ 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;
- }
- queue = Arrays.copyOf(queue, newlen);
+ 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);
}
/**
@@ -304,29 +262,29 @@ 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;
}
@@ -351,6 +309,23 @@ public class PriorityQueue extends Ab
}
/**
+ * Version of remove using reference equality, not equals.
+ * Needed by iterator.remove.
+ *
+ * @param o element to be removed from this queue, if present
+ * @return 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).
@@ -370,10 +345,10 @@ public class PriorityQueue extends Ab
* maintained by this list. (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.
+ * @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);
}
/**
@@ -403,8 +378,8 @@ 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 +395,87 @@ 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.
- */
- private int lastRet = 0;
-
- /**
- * The modCount value that the iterator believes that the backing
- * List should have. If this expectation is violated, the iterator
- * has detected concurrent modification.
+ * Set to -1 if element is deleted by a call to remove.
*/
- private int expectedModCount = modCount;
+ private int lastRet = -1;
/**
- * 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.
*/
- 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
+ * List 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 && lastRetElt == null)
+ throw new IllegalStateException();
+ 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);
- lastRetElt = null;
} else {
- throw new IllegalStateException();
+ PriorityQueue.this.removeEq(lastRetElt);
+ lastRetElt = null;
}
-
expectedModCount = modCount;
}
- final void checkForComodification() {
- if (modCount != expectedModCount)
- throw new ConcurrentModificationException();
- }
}
public int size() {
@@ -524,52 +488,48 @@ 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 traverseing 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 +538,97 @@ 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 super E>)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 super E>)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 super E> key = (Comparable super E>) x;
+ while (k > 0) {
+ int parent = (k - 1) >>> 1;
+ Object e = queue[parent];
+ if (key.compareTo((E)e) >= 0)
+ break;
+ queue[k] = e;
+ k = parent;
+ }
+ queue[k] = key;
+ }
+
+ 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 super E> key = (Comparable super E>)x;
+ int half = size >>> 1; // loop while a non-leaf
+ while (k < half) {
+ int child = (k << 1) + 1; // assume left child is least
+ Object c = queue[child];
+ int right = child + 1;
+ if (right < size &&
+ ((Comparable super E>)c).compareTo((E)queue[right]) > 0)
+ c = queue[child = right];
+ if (key.compareTo((E)c) <= 0)
+ break;
+ queue[k] = c;
+ k = child;
+ }
+ queue[k] = key;
+ }
+
+ 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;
}
/**
@@ -646,8 +636,8 @@ 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]);
}
/**
@@ -678,10 +668,11 @@ public class PriorityQueue extends Ab
s.defaultWriteObject();
// Write out array length
- s.writeInt(queue.length);
+ // For compatibility with 1.5 version, must be at least 2.
+ s.writeInt(Math.max(2, queue.length));
// Write out all elements in the proper order.
- for (int i=1; i<=size; i++)
+ for (int i=0; i extends Ab
queue = new Object[arrayLength];
// Read in all elements in the proper order.
- for (int i=1; i<=size; i++)
+ for (int i=0; i