--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/18 18:10:02 1.2
+++ jsr166/src/main/java/util/PriorityQueue.java 2005/11/24 03:44:57 1.54
@@ -1,57 +1,86 @@
- package java.util;
-
/*
- * Todo
+ * @(#)PriorityQueue.java 1.8 05/08/27
*
- * 1) Make it serializable.
+ * 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 the order specified at creation time. This order is
- * specified as for {@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 {@link #peek}, {@link #poll}, and {@link #remove} methods return the
- * minimal element with respect to the specified ordering. If multiple
- * these elements are tied for least value, no guarantees are made as to
- * which of elements is returned.
+ * 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.
*
- *
Each priority queue has a capacity. The capacity is the size of
- * the 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 list,
- * its capacity grows automatically. The details of the growth policy are not
+ *
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.
*
- *
Implementation note: this implementation provides O(log(n)) time for
- * the offer, poll, remove() and add
- * methods; linear time for the remove(Object) and
- * contains methods; and constant time for the peek,
- * element, and size methods.
+ *
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,
+ * 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).
*
*
This class is a member of the
*
* 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
-{
+ 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
- * of n, d, n <= d.
+ * 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.
+ * 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.
*/
- private E[] queue;
+ private transient Object[] queue;
/**
* The number of elements in the priority queue.
@@ -62,211 +91,420 @@ public class PriorityQueue extends Ab
* The comparator, or null if priority queue uses elements'
* natural ordering.
*/
- private final Comparator comparator;
+ private final Comparator comparator;
/**
* The number of times this priority queue has been
* structurally modified. See AbstractList for gory details.
*/
- private int modCount = 0;
+ private transient int modCount = 0;
/**
- * Create a new priority queue with the default initial capacity (11)
- * that orders its elements according to their natural ordering.
+ * 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);
+ this(DEFAULT_INITIAL_CAPACITY, null);
}
/**
- * Create a new priority queue with the specified initial capacity
- * that orders its elements according to their natural ordering.
+ * 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.
+ * @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 new priority queue with the specified initial capacity (11)
+ * 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.
+ * @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 comparator) {
+ public PriorityQueue(int initialCapacity,
+ Comparator comparator) {
if (initialCapacity < 1)
- initialCapacity = 1;
- queue = new E[initialCapacity + 1];
+ throw new IllegalArgumentException();
+ this.queue = new Object[initialCapacity + 1];
this.comparator = comparator;
}
/**
- * Create a new priority queue 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 the
- * Sorted interface, the priority queue is ordered according to
- * its elements' natural order.
- *
- * @param initialElements 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.
+ * Common code to initialize underlying queue array across
+ * constructors below.
*/
- public PriorityQueue(Collection initialElements) {
- int sz = initialElements.size();
+ 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;
- queue = new E[initialCapacity + 1];
- /* Commented out to compile with generics compiler
+ this.queue = new Object[initialCapacity + 1];
+ }
- if (initialElements instanceof Sorted) {
- comparator = ((Sorted)initialElements).comparator();
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- queue[++size] = i.next();
+ /**
+ * 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.
+ *
+ * @param c the collection whose elements are to be placed
+ * into this priority queue
+ * @throws ClassCastException if elements of the specified collection
+ * cannot be compared to one another according to the priority
+ * queue's ordering
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
+ */
+ 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;
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- add(i.next());
+ fillFromUnsorted(c);
}
}
- // Queue Methods
+ /**
+ * 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
+ * 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 c) {
+ initializeArray(c);
+ comparator = (Comparator)c.comparator();
+ fillFromSorted(c);
+ }
/**
- * Remove and return the minimal element from this priority queue if
- * it contains one or more elements, otherwise null. The term
- * minimal is defined according to this priority queue's order.
+ * 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
+ * according to the same ordering as the given sorted set.
+ *
+ * @param c the sorted set whose elements are to be placed
+ * into this priority queue.
+ * @throws ClassCastException if elements of the specified sorted
+ * set cannot be compared to one another according to the
+ * sorted set's ordering
+ * @throws NullPointerException if the specified sorted set or any
+ * of its elements are null
+ */
+ public PriorityQueue(SortedSet c) {
+ initializeArray(c);
+ comparator = (Comparator)c.comparator();
+ fillFromSorted(c);
+ }
+
+ /**
+ * Resize array, if necessary, to be able to hold given index.
+ */
+ private void grow(int index) {
+ int newlen = queue.length;
+ if (index < newlen) // don't need to grow
+ return;
+ if (index == Integer.MAX_VALUE)
+ throw new OutOfMemoryError();
+ while (newlen <= index) {
+ if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow
+ newlen = Integer.MAX_VALUE;
+ else
+ newlen <<= 1;
+ }
+ queue = Arrays.copyOf(queue, newlen);
+ }
+
+ /**
+ * Inserts the specified element into this priority queue.
*
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
+ * @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 E poll() {
+ 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++;
+ ++size;
+
+ // Grow backing store if necessary
+ if (size >= queue.length)
+ grow(size);
+
+ queue[size] = e;
+ fixUp(size);
+ return true;
+ }
+
+ public E peek() {
if (size == 0)
return null;
- return remove(1);
+ return (E) queue[1];
+ }
+
+ private int indexOf(Object o) {
+ if (o == null)
+ return -1;
+ for (int i = 1; i <= size; i++)
+ if (o.equals(queue[i]))
+ return i;
+ return -1;
}
/**
- * Return, but do not remove, the minimal element from the priority queue,
- * or null if the queue is empty. The term minimal is
- * defined according to this priority queue's order. This method returns
- * the same object reference that would be returned by by the
- * poll method. The two methods differ in that this method
- * does not remove the element from the priority queue.
+ * 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).
*
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
+ * @param o element to be removed from this queue, if present
+ * @return true if this queue changed as a result of the call
*/
- public E peek() {
- return queue[1];
+ public boolean remove(Object o) {
+ int i = indexOf(o);
+ if (i == -1)
+ return false;
+ else {
+ removeAt(i);
+ return true;
+ }
}
- // Collection Methods
+ /**
+ * 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 contains(Object o) {
+ return indexOf(o) != -1;
+ }
/**
- * Removes a single instance of the specified element from this priority
- * queue, if it is present. Returns true if this collection contained the
- * specified element (or equivalently, if this collection changed as a
- * result of the call).
+ * Returns an array containing all of the elements in this queue,
+ * The elements are in no particular order.
*
- * @param o element to be removed from this collection, if present.
- * @return true if this collection changed as a result of the
- * call
- * @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.
+ * 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 element) {
- if (element == null)
- throw new NullPointerException();
+ public Object[] toArray() {
+ return Arrays.copyOfRange(queue, 1, size+1);
+ }
- if (comparator == null) {
- for (int i = 1; i <= size; i++) {
- if (((Comparable)queue[i]).compareTo(element) == 0) {
- remove(i);
- return true;
- }
- }
- } else {
- for (int i = 1; i <= size; i++) {
- if (comparator.compare(queue[i], (E) element) == 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.copyOfRange(queue, 1, size+1, a.getClass());
+ System.arraycopy(queue, 1, a, 0, size);
+ if (a.length > size)
+ a[size] = null;
+ return a;
}
/**
- * Returns an iterator over the elements in this priority queue. The
- * first element returned by this iterator is the same element that
- * would be returned by a call to peek.
+ * 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 {
+
/**
* Index (into queue array) of element to be returned by
* subsequent call to next.
*/
- int cursor = 1;
+ private int cursor = 1;
/**
- * 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.
+ * Reset to 0 if element is deleted by a call to remove.
*/
- int lastRet = 0;
+ 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.
*/
- int expectedModCount = modCount;
+ private int expectedModCount = modCount;
+
+ /**
+ * A list 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
+ * 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;
+
+ /**
+ * Element returned by the most recent call to next iff that
+ * element was drawn from the forgetMeNot list.
+ */
+ private Object lastRetElt = null;
public boolean hasNext() {
- return cursor <= size;
+ return cursor <= size || forgetMeNot != null;
}
public E next() {
checkForComodification();
- if (cursor > size)
+ E result;
+ if (cursor <= size) {
+ result = (E) queue[cursor];
+ lastRet = cursor++;
+ }
+ else if (forgetMeNot == null)
throw new NoSuchElementException();
- E result = queue[cursor];
- lastRet = cursor++;
+ else {
+ int remaining = forgetMeNot.size();
+ result = forgetMeNot.remove(remaining - 1);
+ if (remaining == 1)
+ forgetMeNot = null;
+ lastRet = 0;
+ lastRetElt = result;
+ }
return result;
}
public void remove() {
- if (lastRet == 0)
- throw new IllegalStateException();
checkForComodification();
- PriorityQueue.this.remove(lastRet);
- if (lastRet < cursor)
- cursor--;
- lastRet = 0;
+ if (lastRet != 0) {
+ E moved = PriorityQueue.this.removeAt(lastRet);
+ lastRet = 0;
+ if (moved == null) {
+ cursor--;
+ } else {
+ if (forgetMeNot == null)
+ forgetMeNot = new ArrayList();
+ forgetMeNot.add(moved);
+ }
+ } else if (lastRetElt != null) {
+ PriorityQueue.this.remove(lastRetElt);
+ lastRetElt = null;
+ } else {
+ throw new IllegalStateException();
+ }
+
expectedModCount = modCount;
}
@@ -276,44 +514,13 @@ public class PriorityQueue extends Ab
}
}
- /**
- * Returns the number of elements in this priority queue.
- *
- * @return the number of elements in this priority queue.
- */
public int size() {
return size;
}
/**
- * Add the specified element to this priority queue.
- *
- * @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.
- */
- public boolean offer(E element) {
- if (element == null)
- throw new NullPointerException();
- modCount++;
-
- // Grow backing store if necessary
- if (++size == queue.length) {
- E[] newQueue = new E[2 * queue.length];
- System.arraycopy(queue, 0, newQueue, 0, size);
- queue = newQueue;
- }
-
- queue[size] = element;
- fixUp(size);
- return true;
- }
-
- /**
- * 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++;
@@ -325,23 +532,49 @@ public class PriorityQueue extends Ab
size = 0;
}
+ public E poll() {
+ if (size == 0)
+ return null;
+ 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);
+
+ return result;
+ }
+
/**
- * Removes and returns the ith element from queue. Recall
- * that queue is one-based, so 1 <= i <= size.
+ * Removes and returns the ith element from queue. (Recall that queue
+ * is one-based, so 1 <= i <= size.)
*
- * XXX: Could further special-case i==size, but is it worth it?
- * XXX: Could special-case i==0, but is it worth it?
+ * 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.
*/
- 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];
+ E moved = (E) queue[size];
+ queue[i] = moved;
queue[size--] = null; // Drop extra ref to prevent memory leak
- if (i <= size)
+ if (i <= size) {
fixDown(i);
- return result;
+ if (queue[i] == moved) {
+ fixUp(i);
+ if (queue[i] != moved)
+ return moved;
+ }
+ }
+ return null;
}
/**
@@ -357,17 +590,17 @@ public class PriorityQueue extends Ab
if (comparator == null) {
while (k > 1) {
int j = k >> 1;
- if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
+ if (((Comparable)queue[j]).compareTo((E)queue[k]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object 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)
+ int j = k >>> 1;
+ if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
@@ -385,34 +618,90 @@ public class PriorityQueue extends Ab
private void fixDown(int k) {
int j;
if (comparator == null) {
- while ((j = k << 1) <= size) {
- if (j 0)
+ 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(queue[j]) <= 0)
+
+ if (((Comparable)queue[k]).compareTo((E)queue[j]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object 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)
+ while ((j = k << 1) <= size && (j > 0)) {
+ if (j 0)
j++; // j indexes smallest kid
- if (comparator.compare(queue[k], queue[j]) <= 0)
+ if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
}
/**
- * Returns the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
- *
- * @return the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
+ * 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/2; i >= 1; i--)
+ fixDown(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.
*/
- Comparator comparator() {
+ public Comparator comparator() {
return comparator;
}
+
+ /**
+ * Save the state of the instance to a stream (that
+ * is, serialize 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.
+ * @param s the stream
+ */
+ 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);
+
+ // Write out all elements in the proper order.
+ for (int i=1; i<=size; i++)
+ s.writeObject(queue[i]);
+ }
+
+ /**
+ * Reconstitute the PriorityQueue instance from a stream
+ * (that is, deserialize it).
+ * @param s the stream
+ */
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ // Read in size, and any hidden stuff
+ s.defaultReadObject();
+
+ // Read in array length and allocate array
+ int arrayLength = s.readInt();
+ queue = new Object[arrayLength];
+
+ // Read in all elements in the proper order.
+ for (int i=1; i<=size; i++)
+ queue[i] = (E) s.readObject();
+ }
+
}