--- jsr166/src/main/java/util/PriorityQueue.java 2003/07/28 09:40:07 1.12
+++ jsr166/src/main/java/util/PriorityQueue.java 2005/11/28 02:44:06 1.57
@@ -1,28 +1,49 @@
- package java.util;
+/*
+ * %W% %E%
+ *
+ * Copyright 2005 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 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 TreeSet} and {@link TreeMap}:
- * elements are ordered
- * either according to their natural order (see {@link Comparable}), or
- * according to a {@link Comparator}, depending on which constructor is used.
- * The 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.
+ * 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).
+ *
+ *
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
+ * 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 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.PriorityBlockingQueue} class.
*
*
Implementation note: this implementation provides O(log(n)) time
* for the insertion methods (offer, poll,
@@ -35,27 +56,26 @@
*
* Java Collections Framework.
* @since 1.5
+ * @version 1.8, 08/27/05
* @author Josh Bloch
+ * @param the type of elements held in this collection
*/
public class PriorityQueue extends AbstractQueue
- implements Queue, Sorted, 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 E[] queue;
+ private transient Object[] queue;
/**
* The number of elements in the priority queue.
@@ -66,7 +86,7 @@ public class PriorityQueue extends Ab
* The comparator, or null if priority queue uses elements'
* natural ordering.
*/
- private final Comparator comparator;
+ private final Comparator super E> comparator;
/**
* The number of times this priority queue has been
@@ -75,187 +95,337 @@ public class PriorityQueue extends Ab
private transient int modCount = 0;
/**
- * Create a PriorityQueue with the default initial capacity
- * (11) that orders its elements according to their natural
- * ordering (using Comparable.)
+ * Creates a 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);
}
/**
- * Create 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 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
*/
public PriorityQueue(int initialCapacity) {
this(initialCapacity, null);
}
/**
- * Create a PriorityQueue with the specified initial capacity
+ * Creates a 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.
- */
- 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 null, the natural
+ * ordering of the elements will be used.
+ * @throws IllegalArgumentException if initialCapacity is
+ * less than 1
+ */
+ 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)
- initialCapacity = 1;
- queue = (E[]) new Object[initialCapacity + 1];
+ throw new IllegalArgumentException();
+ this.queue = new Object[initialCapacity];
this.comparator = comparator;
}
/**
- * Create 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. If the specified collection
- * implements the {@link Sorted} interface, the priority queue will be
- * sorted according to the same comparator, or according to its elements'
- * natural order if the collection is sorted according to its elements'
- * natural order. If the specified collection does not implement
- * Sorted, the priority queue is ordered according to
- * its elements' natural order.
+ * Creates a PriorityQueue containing the elements in the
+ * 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
+ * will be ordered according to the natural ordering of its elements.
*
- * @param initialElements the collection whose elements are to be placed
- * into this priority queue.
+ * @param c the collection whose elements are to be placed
+ * into this priority queue
* @throws ClassCastException if elements of the specified collection
* cannot be compared to one another according to the priority
- * queue's ordering.
- * @throws NullPointerException if the specified collection or an
- * element of the specified collection is null.
- */
- public PriorityQueue(Collection initialElements) {
- int sz = initialElements.size();
- int initialCapacity = (int)Math.min((sz * 110L) / 100,
- Integer.MAX_VALUE - 1);
- if (initialCapacity < 1)
- initialCapacity = 1;
- queue = (E[]) new Object[initialCapacity + 1];
-
- if (initialElements instanceof Sorted) {
- comparator = ((Sorted)initialElements).comparator();
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- queue[++size] = i.next();
- } else {
+ * queue's ordering
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
+ */
+ public PriorityQueue(Collection extends E> c) {
+ 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;
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- add(i.next());
+ heapify();
}
}
- // Queue Methods
+ /**
+ * Creates a 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
+ * ordering
+ * @throws NullPointerException if the specified priority queue or any
+ * of its elements are null
+ */
+ public PriorityQueue(PriorityQueue extends E> c) {
+ comparator = (Comparator super E>)c.comparator();
+ initFromCollection(c);
+ }
/**
- * Add the specified element to this priority queue.
+ * Creates a 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 element the element to add.
- * @return true
- * @throws ClassCastException if the specified element cannot be compared
- * with elements currently in the priority queue according
- * to the priority queue's ordering.
- * @throws NullPointerException if the specified element is null.
+ * @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 boolean offer(E element) {
- if (element == null)
- throw new NullPointerException();
- modCount++;
- ++size;
+ public PriorityQueue(SortedSet extends E> c) {
+ comparator = (Comparator super E>)c.comparator();
+ initFromCollection(c);
+ }
- // Grow backing store if necessary
- while (size >= queue.length) {
- E[] newQueue = (E[]) new Object[2 * queue.length];
- System.arraycopy(queue, 0, newQueue, 0, queue.length);
- queue = newQueue;
- }
+ /**
+ * Initialize queue array with elements from the given Collection.
+ * @param c the collection
+ */
+ 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;
+ }
- queue[size] = element;
- fixUp(size);
+ /**
+ * Increases the capacity of the array.
+ *
+ * @param minCapacity the desired minimum capacity
+ */
+ private void grow(int minCapacity) {
+ if (minCapacity < 0) // overflow
+ throw new OutOfMemoryError();
+ int oldCapacity = queue.length;
+ // Double size if small; else grow by 50%
+ int newCapacity = ((oldCapacity < 64)?
+ ((oldCapacity + 1) * 2):
+ ((oldCapacity * 3) / 2));
+ if (newCapacity < minCapacity)
+ newCapacity = minCapacity;
+ queue = Arrays.copyOf(queue, newCapacity);
+ }
+
+ /**
+ * Inserts the specified element into this priority queue.
+ *
+ * @return 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);
+ }
+
+ /**
+ * Inserts the specified element into this priority queue.
+ *
+ * @return true (as specified by {@link Queue#offer})
+ * @throws ClassCastException if the specified element cannot be
+ * compared with elements currently in this priority queue
+ * according to the priority queue's ordering
+ * @throws NullPointerException if the specified element is null
+ */
+ public boolean offer(E e) {
+ if (e == null)
+ throw new NullPointerException();
+ modCount++;
+ int i = size;
+ if (i >= queue.length)
+ grow(i + 1);
+ 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 remove(1);
+ return (E) queue[0];
}
- public E peek() {
- return 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 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).
+ *
+ * @param o element to be removed from this queue, if present
+ * @return 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 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.
+ * 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).
+ *
+ * @param o object to be checked for containment in this queue
+ * @return true if this queue contains the specified element
*/
- public boolean add(E element) {
- return super.add(element);
+ public boolean contains(Object o) {
+ return indexOf(o) != -1;
}
- // /**
- // * @throws NullPointerException if any element is null.
- // */
- // public boolean addAll(Collection c) {
- // return super.addAll(c);
- // }
-
/**
- * @throws NullPointerException if the specified element 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 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.
*/
- public boolean remove(Object o) {
- if (o == null)
- throw new NullPointerException();
+ public Object[] toArray() {
+ return Arrays.copyOf(queue, size);
+ }
- if (comparator == null) {
- for (int i = 1; i <= size; i++) {
- if (((Comparable)queue[i]).compareTo(o) == 0) {
- remove(i);
- return true;
- }
- }
- } else {
- for (int i = 1; i <= size; i++) {
- if (comparator.compare(queue[i], (E)o) == 0) {
- remove(i);
- return true;
- }
- }
- }
- return false;
+ /**
+ * 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.
+ *
+ *
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.)
+ *
+ * @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
+ * @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 priority queue. The
- * elements of the priority queue will be returned by this iterator in the
- * order specified by the queue, which is to say the order they would be
- * returned by repeated calls to poll.
+ * 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 priority 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 = 0;
+
+ /**
+ * Index of element returned by most recent call to next,
+ * unless that element came from the forgetMeNot list.
+ * Set to -1 if element is deleted by a call to remove.
+ */
+ private int lastRet = -1;
+
+ /**
+ * A queue of elements that were moved from the unvisited portion of
+ * the heap into the visited portion as a result of "unlucky" element
+ * removals during the iteration. (Unlucky element removals are those
+ * that require a siftup instead of a siftdown.) We must visit all of
+ * the elements in this list to complete the iteration. We do this
+ * after we've completed the "normal" iteration.
+ *
+ * We expect that most iterations, even those involving removals,
+ * will not use need to store elements in this field.
+ */
+ private ArrayDeque forgetMeNot = null;
/**
- * Index of element returned by most recent call to next or
- * previous. Reset to 0 if this element is deleted by a call
- * to remove.
+ * Element returned by the most recent call to next iff that
+ * element was drawn from the forgetMeNot list.
*/
- private int lastRet = 0;
+ private E lastRetElt = null;
/**
* The modCount value that the iterator believes that the backing
@@ -265,139 +435,220 @@ public class PriorityQueue extends Ab
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 = 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 && lastRetElt == null)
throw new IllegalStateException();
- checkForComodification();
-
- PriorityQueue.this.remove(lastRet);
- if (lastRet < cursor)
- cursor--;
- lastRet = 0;
+ 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 {
+ PriorityQueue.this.removeEq(lastRetElt);
+ lastRetElt = null;
+ }
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 traverseing elements.
*/
- private E remove(int i) {
- assert i <= size;
+ private E removeAt(int i) {
+ assert i >= 0 && i < size;
modCount++;
-
- E result = queue[i];
- queue[i] = queue[size];
- queue[size--] = null; // Drop extra ref to prevent memory leak
- if (i <= size)
- fixDown(i);
- return result;
+ 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(queue[k]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
- }
- } else {
- while (k > 1) {
- int j = k >> 1;
- if (comparator.compare(queue[j], queue[k]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
- }
+ * 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;
}
/**
- * Establishes the heap invariant (described above) in the subtree
- * rooted at k, which is assumed to satisfy the heap invariant except
- * possibly for node k itself (which may be greater than its children).
- *
- * This method functions by "demoting" queue[k] down the hierarchy
- * (by swapping it with its smaller child) repeatedly until queue[k]
- * is less than or equal to its children.
- */
- private void fixDown(int k) {
- int j;
- if (comparator == null) {
- while ((j = k << 1) <= size) {
- if (j 0)
- j++; // j indexes smallest kid
- if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
- }
- } else {
- while ((j = k << 1) <= size) {
- if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
- j++; // j indexes smallest kid
- if (comparator.compare(queue[k], queue[j]) <= 0)
- break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
- k = j;
- }
+ * 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;
}
- public Comparator comparator() {
+ 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 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.
+ */
+ public Comparator super E> comparator() {
return comparator;
}
@@ -410,13 +661,14 @@ public class PriorityQueue extends Ab
* Object) in the proper order.
* @param s the stream
*/
- private synchronized void writeObject(java.io.ObjectOutputStream s)
+ private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException{
// Write out element count, and any hidden stuff
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=0; i extends Ab
}
/**
- * Reconstitute the ArrayList instance from a stream (that is,
- * deserialize it).
+ * Reconstitute the PriorityQueue instance from a stream
+ * (that is, deserialize it).
* @param s the stream
*/
- private synchronized void readObject(java.io.ObjectInputStream s)
+ 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 = (E[]) new Object[arrayLength];
+ queue = new Object[arrayLength];
// Read in all elements in the proper order.
for (int i=0; i