--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/18 18:10:02 1.2
+++ jsr166/src/main/java/util/PriorityQueue.java 2003/07/28 09:40:07 1.12
@@ -1,57 +1,61 @@
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.
+ * 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.
*
- *
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.
+ *
The {@link #element()} and {@link #peek()} methods return, but do
+ * not delete, the head of the queue.
*
- *
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.
+ *
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 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, Sorted, 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.
@@ -68,19 +72,21 @@ 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 PriorityQueue with the default initial capacity
+ * (11) that orders its elements according to their natural
+ * ordering (using Comparable.)
*/
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.
+ * 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.
*/
@@ -89,28 +95,30 @@ public class PriorityQueue extends Ab
}
/**
- * Create a new priority queue with the specified initial capacity (11)
+ * Create 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) {
if (initialCapacity < 1)
initialCapacity = 1;
- queue = new E[initialCapacity + 1];
+ queue = (E[]) new Object[initialCapacity + 1];
this.comparator = comparator;
}
/**
- * Create a new priority queue containing the elements in the specified
+ * 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 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
@@ -127,17 +135,13 @@ public class PriorityQueue extends Ab
Integer.MAX_VALUE - 1);
if (initialCapacity < 1)
initialCapacity = 1;
- queue = new E[initialCapacity + 1];
-
- /* Commented out to compile with generics compiler
+ 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 {
- */
- {
comparator = null;
for (Iterator i = initialElements.iterator(); i.hasNext(); )
add(i.next());
@@ -147,64 +151,78 @@ 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.
+ * Add the specified element to this priority queue.
*
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
+ * @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++;
+ ++size;
+
+ // 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;
+ }
+
+ queue[size] = element;
+ fixUp(size);
+ return true;
+ }
+
public E poll() {
if (size == 0)
return null;
return remove(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.
- *
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
- */
public E peek() {
return queue[1];
}
// Collection Methods
+ // these first two override just to get the throws docs
+
/**
- * 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).
- *
- * @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.
+ * @throws NullPointerException if the specified element is null.
*/
- public boolean remove(Object element) {
- if (element == null)
+ public boolean add(E element) {
+ return super.add(element);
+ }
+
+ // /**
+ // * @throws NullPointerException if any element is null.
+ // */
+ // public boolean addAll(Collection c) {
+ // return super.addAll(c);
+ // }
+
+ /**
+ * @throws NullPointerException if the specified element is null.
+ */
+ public boolean remove(Object o) {
+ if (o == null)
throw new NullPointerException();
if (comparator == null) {
for (int i = 1; i <= size; i++) {
- if (((Comparable)queue[i]).compareTo(element) == 0) {
+ 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) element) == 0) {
+ if (comparator.compare(queue[i], (E)o) == 0) {
remove(i);
return true;
}
@@ -215,8 +233,9 @@ 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.
*/
@@ -229,21 +248,21 @@ 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;
@@ -286,33 +305,6 @@ public class PriorityQueue extends Ab
}
/**
- * 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.
*/
public void clear() {
@@ -405,14 +397,50 @@ public class PriorityQueue extends Ab
}
}
+ public Comparator comparator() {
+ return comparator;
+ }
+
/**
- * Returns the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
+ * Save the state of the instance to a stream (that
+ * is, serialize it).
*
- * @return the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
+ * @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
*/
- Comparator comparator() {
- return comparator;
+ 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 = (E[]) new Object[arrayLength];
+
+ // Read in all elements in the proper order.
+ for (int i=0; i