--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/19 02:45:07 1.4 +++ jsr166/src/main/java/util/PriorityQueue.java 2003/07/13 22:51:22 1.9 @@ -1,57 +1,54 @@ package java.util; -/* - * Todo - * - * 1) Make it serializable. - */ - /** * 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 + * 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 {@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. + * elements are tied for least value, no guarantees are made as to + * which of these elements is returned. * - *

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 - * 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. * - *

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. + *

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 + * @author Josh Bloch */ public class PriorityQueue extends AbstractQueue - implements Queue -{ + implements Queue, + java.io.Serializable { 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 E[] queue; /** * The number of elements in the priority queue. @@ -68,11 +65,12 @@ public class PriorityQueue extends Ab * 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. + * Create a new priority queue with the default initial capacity + * (11) that orders its elements according to their natural + * ordering (using Comparable.) */ public PriorityQueue() { this(DEFAULT_INITIAL_CAPACITY); @@ -80,7 +78,8 @@ public class PriorityQueue extends Ab /** * Create a new priority queue with the specified initial capacity - * that orders its elements according to their natural ordering. + * that orders its elements according to their natural ordering + * (using Comparable.) * * @param initialCapacity the initial capacity for this priority queue. */ @@ -109,8 +108,8 @@ public class PriorityQueue extends Ab * 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 + * natural order. If the specified collection does not implement + * Sorted, the priority queue is ordered according to * its elements' natural order. * * @param initialElements the collection whose elements are to be placed @@ -129,6 +128,7 @@ public class PriorityQueue extends Ab initialCapacity = 1; queue = new E[initialCapacity + 1]; + if (initialElements instanceof Sorted) { comparator = ((Sorted)initialElements).comparator(); for (Iterator i = initialElements.iterator(); i.hasNext(); ) @@ -143,9 +143,10 @@ public class PriorityQueue extends Ab // Queue Methods /** - * 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. + * Remove and return the minimal element from this priority queue + * if it contains one or more elements, otherwise return + * null. The term minimal is defined according to + * this priority queue's order. * * @return the minimal element from this priority queue if it contains * one or more elements, otherwise null. @@ -157,12 +158,13 @@ public class PriorityQueue extends Ab } /** - * 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. + * Return, but do not remove, the minimal element from the + * priority queue, or return 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. * * @return the minimal element from this priority queue if it contains * one or more elements, otherwise null. @@ -179,7 +181,8 @@ public class PriorityQueue extends Ab * specified element (or equivalently, if this collection changed as a * result of the call). * - * @param o element to be removed from this collection, if present. + * @param element the 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 @@ -211,9 +214,10 @@ public class PriorityQueue extends Ab /** * 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. - * + * 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. + * * @return an Iterator over the elements in this priority queue. */ public Iterator iterator() { @@ -225,21 +229,21 @@ public class PriorityQueue extends Ab * 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. */ - 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; public boolean hasNext() { return cursor <= size; @@ -274,7 +278,7 @@ 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() { @@ -295,11 +299,12 @@ public class PriorityQueue extends Ab if (element == null) throw new NullPointerException(); modCount++; + ++size; // Grow backing store if necessary - if (++size == queue.length) { + while (size >= queue.length) { E[] newQueue = new E[2 * queue.length]; - System.arraycopy(queue, 0, newQueue, 0, size); + System.arraycopy(queue, 0, newQueue, 0, queue.length); queue = newQueue; } @@ -408,7 +413,49 @@ public class PriorityQueue extends Ab * @return the comparator associated with this priority queue, or * null if it uses its elements' natural ordering. */ - 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 synchronized 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=0; iArrayList instance from a stream (that is, + * deserialize it). + * @param s the stream + */ + private synchronized 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 E[arrayLength]; + + // Read in all elements in the proper order. + for (int i=0; i