--- jsr166/src/main/java/util/PriorityQueue.java 2003/08/04 01:48:39 1.18 +++ jsr166/src/main/java/util/PriorityQueue.java 2005/11/29 08:52:26 1.59 @@ -1,31 +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) /** - * A priority queue based on a priority heap. This queue orders - * elements according to an order specified at construction time, which is - * specified in the same manner as {@link java.util.TreeSet} and - * {@link java.util.TreeMap}: elements are ordered - * either according to their natural order (see {@link Comparable}), or - * according to a {@link java.util.Comparator}, depending on which - * constructor is used. - *

The head of this queue is the least element with - * respect to the specified ordering. - * If multiple elements are tied for least value, the - * head is one of those elements. A priority queue does not permit - * null elements. + * An unbounded priority {@linkplain Queue queue} based on a priority + * heap. The elements of the priority queue are ordered according to + * their {@linkplain Comparable natural ordering}, or by a {@link + * Comparator} provided at queue construction time, depending on which + * constructor is used. A priority queue does not permit + * 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 #remove()} and {@link #poll()} methods remove and - * return 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. * - *

The {@link #element()} and {@link #peek()} methods return, but do - * not delete, the head of the queue. + *

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()). * - *

A priority queue has a capacity. The capacity is the - * size of the array used internally to store the elements on the - * queue, and is limited to Integer.MAX_VALUE-1. - * 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. + *

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, @@ -38,25 +56,24 @@ * * 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 Sorted, Queue, java.io.Serializable { + implements java.io.Serializable { + + private static final long serialVersionUID = -7720805057305804111L; private static final int DEFAULT_INITIAL_CAPACITY = 11; /** - * Priority queue represented as a balanced binary heap: the two children - * of queue[n] are queue[2*n] and queue[2*n + 1]. The priority queue is - * ordered by comparator, or by the elements' natural ordering, if - * comparator is null: For each node n in the heap and each descendant d - * of n, n <= d. - * - * The element with the lowest value is in queue[1], assuming the queue is - * nonempty. (A one-based array is used in preference to the traditional - * zero-based array to simplify parent and child calculations.) - * - * queue.length must be >= 2, even if size == 0. + * Priority queue represented as a balanced binary heap: the two + * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The + * priority queue is ordered by comparator, or by the elements' + * natural ordering, if comparator is null: For each node n in the + * heap and each descendant d of n, n <= d. The element with the + * lowest value is in queue[0], assuming the queue is nonempty. */ private transient Object[] queue; @@ -78,191 +95,339 @@ 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.) + * 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 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. - * @throws IllegalArgumentException if initialCapacity is less - * than 1 - */ - public PriorityQueue(int initialCapacity, Comparator comparator) { + * @param initialCapacity the initial capacity for this priority queue + * @param comparator the comparator that will be used to order + * this priority queue. If null, the natural + * ordering of the elements will be used. + * @throws IllegalArgumentException if 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; } /** - * 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 (bounded by - * Integer.MAX_VALUE-1); or 1 if the collection is empty. - * 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 c the collection whose elements are to be placed - * into this priority queue. + * @param c the collection whose elements are to be placed + * into this priority queue * @throws ClassCastException if elements of the specified collection * cannot be compared to one another according to the priority - * queue's ordering. - * @throws NullPointerException if c or any element within it - * is null + * queue's ordering + * @throws NullPointerException if the specified collection or any + * of its elements are null */ public PriorityQueue(Collection c) { - int sz = c.size(); - int initialCapacity = (int)Math.min((sz * 110L) / 100, - Integer.MAX_VALUE - 1); - if (initialCapacity < 1) - initialCapacity = 1; + initFromCollection(c); + if (c instanceof SortedSet) + comparator = (Comparator) + ((SortedSet)c).comparator(); + else if (c instanceof PriorityQueue) + comparator = (Comparator) + ((PriorityQueue)c).comparator(); + else { + comparator = null; + heapify(); + } + } - this.queue = new Object[initialCapacity + 1]; + /** + * 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 c) { + comparator = (Comparator)c.comparator(); + initFromCollection(c); + } - // FIXME: if c is larger than Integer.MAX_VALUE we'll - // overflow the array + /** + * 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 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) { + comparator = (Comparator)c.comparator(); + initFromCollection(c); + } - if (c instanceof Sorted) { - comparator = ((Sorted)c).comparator(); - } else { - comparator = null; - } + /** + * Initialize queue array with elements from the given Collection. + * @param c the collection + */ + private void initFromCollection(Collection c) { + Object[] a = c.toArray(); + // If c.toArray incorrectly doesn't return Object[], copy it. + if (a.getClass() != Object[].class) + a = Arrays.copyOf(a, a.length, Object[].class); + queue = a; + size = a.length; + } - for (Iterator i = c.iterator(); i.hasNext(); ) - add(i.next()); + /** + * 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 / 2) * 3)); + if (newCapacity < 0) // overflow + newCapacity = Integer.MAX_VALUE; + if (newCapacity < minCapacity) + newCapacity = minCapacity; + queue = Arrays.copyOf(queue, newCapacity); } - // Queue Methods + /** + * 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); + } /** - * Add the specified element to this priority queue. + * Inserts the specified element into this priority queue. * - * @return true - * @throws ClassCastException if the specified element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. - * @throws NullPointerException if the specified element is null. + * @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 o) { - if (o == null) + public boolean offer(E e) { + if (e == null) throw new NullPointerException(); modCount++; - ++size; - - // Grow backing store if necessary - // FIXME: watch for overflow - // FIXME: what if we're full? - while (size >= queue.length) { - Object[] newQueue = new Object[2 * queue.length]; - System.arraycopy(queue, 0, newQueue, 0, queue.length); - queue = newQueue; - } - - queue[size] = o; - fixUp(size); + int i = size; + if (i >= queue.length) + grow(i + 1); + size = i + 1; + if (i == 0) + queue[0] = e; + else + siftUp(i, e); return true; } - public E poll() { + public E peek() { if (size == 0) return null; - return (E) remove(1); + return (E) queue[0]; } - public E peek() { - return (E) queue[1]; + private int indexOf(Object o) { + if (o != null) { + for (int i = 0; i < size; i++) + if (o.equals(queue[i])) + return i; + } + return -1; } - // Collection Methods + /** + * Removes a single instance of the specified element from this queue, + * if it is present. More formally, removes an element 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. - * @throws ClassCastException if the specified element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. + * 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 o) { - return super.add(o); + public boolean contains(Object o) { + return indexOf(o) != -1; } /** - * @throws ClassCastException if any element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. - * @throws NullPointerException if c or any element in c - * is null + * Returns an array containing all of the elements in this queue, + * The elements are in no particular order. + * + *

The returned array will be "safe" in that no references to it are + * maintained by this 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 addAll(Collection c) { - return super.addAll(c); + public Object[] toArray() { + return Arrays.copyOf(queue, size); } - public boolean remove(Object o) { - if (o == null) - return false; - - if (comparator == null) { - for (int i = 1; i <= size; i++) { - if (((Comparable)queue[i]).compareTo((E)o) == 0) { - remove(i); - return true; - } - } - } else { - for (int i = 1; i <= size; i++) { - if (comparator.compare((E)queue[i], (E)o) == 0) { - remove(i); - return true; - } - } - } - return false; + /** + * Returns an array containing all of the elements in this queue. + * The 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 queue. The iterator + * does not return the elements in any particular order. + * + * @return an iterator over the elements in this queue + */ public Iterator iterator() { return new Itr(); } - private class Itr implements Iterator { + private final class Itr implements Iterator { /** * Index (into queue array) of element to be returned by * subsequent call to next. */ - private int cursor = 1; + private int cursor = 0; /** - * Index of element returned by most recent call to next or - * previous. Reset to 0 if this element is deleted by a call - * to remove. + * Index of element returned by most recent call to next, + * unless that element came from the forgetMeNot list. + * Set to -1 if element is deleted by a call to remove. */ - private int lastRet = 0; + private int lastRet = -1; + + /** + * A queue of elements that were moved from the unvisited portion of + * the heap into the visited portion as a result of "unlucky" element + * removals during the iteration. (Unlucky element removals are those + * that require a siftup instead of a siftdown.) We must visit all of + * the elements in this list to complete the iteration. We do this + * after we've completed the "normal" iteration. + * + * We expect that most iterations, even those involving removals, + * will not use need to store elements in this field. + */ + private ArrayDeque forgetMeNot = null; + + /** + * Element returned by the most recent call to next iff that + * element was drawn from the forgetMeNot list. + */ + private E lastRetElt = null; /** * The modCount value that the iterator believes that the backing @@ -272,138 +437,219 @@ 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 = (E) queue[cursor]; - lastRet = cursor++; - return result; + if (expectedModCount != modCount) + throw new ConcurrentModificationException(); + if (cursor < size) + return (E) queue[lastRet = cursor++]; + if (forgetMeNot != null) { + lastRet = -1; + lastRetElt = forgetMeNot.poll(); + if (lastRetElt != null) + return lastRetElt; + } + throw new NoSuchElementException(); } public void remove() { - if (lastRet == 0) + if (expectedModCount != modCount) + throw new ConcurrentModificationException(); + if (lastRet == -1 && 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 = (E) queue[i]; - queue[i] = queue[size]; - queue[size--] = null; // Drop extra ref to prevent memory leak - if (i <= size) - fixDown(i); - return result; + int s = --size; + if (s == i) // removed last element + queue[i] = null; + else { + E moved = (E) queue[s]; + queue[s] = null; + siftDown(i, moved); + if (queue[i] == moved) { + siftUp(i, moved); + if (queue[i] != moved) + return moved; + } + } + return null; } /** - * Establishes the heap invariant (described above) assuming the heap - * satisfies the invariant except possibly for the leaf-node indexed by k - * (which may have a nextExecutionTime less than its parent's). - * - * This method functions by "promoting" queue[k] up the hierarchy - * (by swapping it with its parent) repeatedly until queue[k] - * is greater than or equal to its parent. - */ - private void fixUp(int k) { - if (comparator == null) { - while (k > 1) { - int j = k >> 1; - if (((Comparable)queue[j]).compareTo((E)queue[k]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } - } else { - while (k > 1) { - int j = k >> 1; - if (comparator.compare((E)queue[j], (E)queue[k]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } + * Inserts item x at position k, maintaining heap invariant by + * promoting x up the tree until it is greater than or equal to + * its parent, or is the root. + * + * To simplify and speed up coercions and comparisons. the + * Comparable and Comparator versions are separated into different + * methods that are otherwise identical. (Similarly for siftDown.) + * + * @param k the position to fill + * @param x the item to insert + */ + private void siftUp(int k, E x) { + if (comparator != null) + siftUpUsingComparator(k, x); + else + siftUpComparable(k, x); + } + + private void siftUpComparable(int k, E x) { + Comparable key = (Comparable) x; + while (k > 0) { + int parent = (k - 1) >>> 1; + Object e = queue[parent]; + if (key.compareTo((E)e) >= 0) + break; + queue[k] = e; + k = parent; } + queue[k] = key; + } + + private void siftUpUsingComparator(int k, E x) { + while (k > 0) { + int parent = (k - 1) >>> 1; + Object e = queue[parent]; + if (comparator.compare(x, (E)e) >= 0) + break; + queue[k] = e; + k = parent; + } + queue[k] = x; } /** - * Establishes the heap invariant (described above) in the subtree - * rooted at k, which is assumed to satisfy the heap invariant except - * possibly for node k itself (which may be greater than its children). - * - * This method functions by "demoting" queue[k] down the hierarchy - * (by swapping it with its smaller child) repeatedly until queue[k] - * is less than or equal to its children. - */ - private void fixDown(int k) { - int j; - if (comparator == null) { - while ((j = k << 1) <= size) { - if (j)queue[j]).compareTo((E)queue[j+1]) > 0) - j++; // j indexes smallest kid - if (((Comparable)queue[k]).compareTo((E)queue[j]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } - } else { - while ((j = k << 1) <= size) { - if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0) - j++; // j indexes smallest kid - if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } + * Inserts item x at position k, maintaining heap invariant by + * demoting x down the tree repeatedly until it is less than or + * equal to its children or is a leaf. + * + * @param k the position to fill + * @param x the item to insert + */ + private void siftDown(int k, E x) { + if (comparator != null) + siftDownUsingComparator(k, x); + else + siftDownComparable(k, x); + } + + private void siftDownComparable(int k, E x) { + Comparable key = (Comparable)x; + int half = size >>> 1; // loop while a non-leaf + while (k < half) { + int child = (k << 1) + 1; // assume left child is least + Object c = queue[child]; + int right = child + 1; + if (right < size && + ((Comparable)c).compareTo((E)queue[right]) > 0) + c = queue[child = right]; + if (key.compareTo((E)c) <= 0) + break; + queue[k] = c; + k = child; } + queue[k] = key; } + private void siftDownUsingComparator(int k, E x) { + int half = size >>> 1; + while (k < half) { + int child = (k << 1) + 1; + Object c = queue[child]; + int right = child + 1; + if (right < size && + comparator.compare((E)c, (E)queue[right]) > 0) + c = queue[child = right]; + if (comparator.compare(x, (E)c) <= 0) + break; + queue[k] = c; + k = child; + } + queue[k] = x; + } + + /** + * Establishes the heap invariant (described above) in the entire tree, + * assuming nothing about the order of the elements prior to the call. + */ + private void heapify() { + for (int i = (size >>> 1) - 1; i >= 0; i--) + siftDown(i, (E)queue[i]); + } + + /** + * Returns the comparator used to order the elements in this + * queue, or 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 comparator() { return comparator; } @@ -417,13 +663,14 @@ 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(); @@ -446,8 +693,7 @@ public class PriorityQueue extends Ab // Read in all elements in the proper order. for (int i=0; i