--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/18 20:36:01 1.3
+++ 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
@@ -129,15 +128,12 @@ public class PriorityQueue extends Ab
initialCapacity = 1;
queue = new E[initialCapacity + 1];
- /* Commented out to compile with generics compiler
if (initialElements instanceof Sorted) {
comparator = ((Sorted)initialElements).comparator();
for (Iterator i = initialElements.iterator(); i.hasNext(); )
queue[++size] = i.next();
} else {
- */
- {
comparator = null;
for (Iterator i = initialElements.iterator(); i.hasNext(); )
add(i.next());
@@ -147,9 +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.
@@ -161,12 +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.
@@ -183,7 +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
@@ -215,9 +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() {
@@ -229,21 +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;
@@ -278,7 +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() {
@@ -299,11 +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;
}
@@ -412,7 +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