--- jsr166/src/main/java/util/PriorityQueue.java 2003/07/31 19:49:42 1.17
+++ jsr166/src/main/java/util/PriorityQueue.java 2003/08/25 23:50:24 1.33
@@ -1,14 +1,17 @@
package java.util;
/**
- * An unbounded priority queue based on a priority heap. This queue orders
+ * An unbounded priority {@linkplain Queue 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
+ * 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
+ * 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.
*
@@ -20,10 +23,23 @@
*
*
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
+ * 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 Iterator provided in method {@link #iterator()} is not
+ * guaranteed to traverse the elements of the PriorityQueue 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.BlockingPriorityQueue} class.
+ *
+ *
*
Implementation note: this implementation provides O(log(n)) time
* for the insertion methods (offer, poll,
* remove() and add) methods; linear time for the
@@ -40,6 +56,8 @@
public class PriorityQueue extends AbstractQueue
implements Queue, java.io.Serializable {
+ private static final long serialVersionUID = -7720805057305804111L;
+
private static final int DEFAULT_INITIAL_CAPACITY = 11;
/**
@@ -75,27 +93,29 @@ public class PriorityQueue extends Ab
private transient int modCount = 0;
/**
- * Create a PriorityQueue with the default initial capacity
+ * Creates a PriorityQueue with the default initial capacity
* (11) that orders its elements according to their natural
- * ordering (using Comparable.)
+ * ordering (using Comparable).
*/
public PriorityQueue() {
this(DEFAULT_INITIAL_CAPACITY, null);
}
/**
- * Create a PriorityQueue with the specified initial capacity
+ * Creates a PriorityQueue with the specified initial capacity
* that orders its elements according to their natural ordering
- * (using Comparable.)
+ * (using Comparable).
*
* @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.
@@ -105,7 +125,8 @@ public class PriorityQueue extends Ab
* @throws IllegalArgumentException if initialCapacity is less
* than 1
*/
- public PriorityQueue(int initialCapacity, Comparator super E> comparator) {
+ public PriorityQueue(int initialCapacity,
+ Comparator super E> comparator) {
if (initialCapacity < 1)
throw new IllegalArgumentException();
this.queue = new Object[initialCapacity + 1];
@@ -113,16 +134,51 @@ public class PriorityQueue extends Ab
}
/**
- * 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; 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.
+ * Common code to initialize underlying queue array across
+ * constructors below.
+ */
+ private void initializeArray(Collection extends E> c) {
+ int sz = c.size();
+ int initialCapacity = (int)Math.min((sz * 110L) / 100,
+ Integer.MAX_VALUE - 1);
+ if (initialCapacity < 1)
+ initialCapacity = 1;
+
+ this.queue = new Object[initialCapacity + 1];
+ }
+
+ /**
+ * 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 without fixups.
+ */
+ private void fillFromSorted(Collection extends E> c) {
+ for (Iterator extends E> i = c.iterator(); i.hasNext(); )
+ queue[++size] = i.next();
+ }
+
+
+ /**
+ * Initially fill elements of the queue array that is
+ * not to our knowledge sorted, so we must add them
+ * one by one.
+ */
+ private void fillFromUnsorted(Collection extends E> c) {
+ for (Iterator extends E> i = c.iterator(); i.hasNext(); )
+ add(i.next());
+ }
+
+ /**
+ * 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 sorted
+ * according to the same comparator, or according to its elements'
+ * natural order if the collection is sorted according to its
+ * elements' natural order. Otherwise, the priority queue is
+ * ordered according to its elements' natural order.
*
* @param c the collection whose elements are to be placed
* into this priority queue.
@@ -133,52 +189,112 @@ public class PriorityQueue extends Ab
* is null
*/
public PriorityQueue(Collection extends E> c) {
- int sz = c.size();
- int initialCapacity = (int)Math.min((sz * 110L) / 100,
- Integer.MAX_VALUE - 1);
- if (initialCapacity < 1)
- initialCapacity = 1;
-
- this.queue = new Object[initialCapacity + 1];
-
- if (c instanceof Sorted) {
- // FIXME: this code assumes too much
- this.comparator = (Comparator super E>) ((Sorted)c).comparator();
- for (Iterator extends E> i = c.iterator(); i.hasNext(); )
- queue[++size] = i.next();
+ initializeArray(c);
+ if (c instanceof SortedSet) {
+ // @fixme double-cast workaround for compiler
+ SortedSet extends E> s = (SortedSet extends E>) (SortedSet)c;
+ comparator = (Comparator super E>)s.comparator();
+ fillFromSorted(s);
+ } else if (c instanceof PriorityQueue) {
+ PriorityQueue extends E> s = (PriorityQueue extends E>) c;
+ comparator = (Comparator super E>)s.comparator();
+ fillFromSorted(s);
} else {
comparator = null;
- for (Iterator extends E> i = c.iterator(); i.hasNext(); )
- add(i.next());
+ fillFromUnsorted(c);
}
}
+ /**
+ * 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. This priority queue will be sorted
+ * according to the same comparator as the given collection, or
+ * according to its elements' natural order if the collection is
+ * sorted according to its elements' natural order.
+ *
+ * @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
+ */
+ public PriorityQueue(PriorityQueue extends E> c) {
+ initializeArray(c);
+ comparator = (Comparator super E>)c.comparator();
+ fillFromSorted(c);
+ }
+
+ /**
+ * 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. This priority queue will be sorted
+ * according to the same comparator as the given collection, or
+ * according to its elements' natural order if the collection is
+ * sorted according to its elements' natural order.
+ *
+ * @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
+ */
+ public PriorityQueue(SortedSet extends E> c) {
+ initializeArray(c);
+ comparator = (Comparator super E>)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 <<= 2;
+ }
+ Object[] newQueue = new Object[newlen];
+ System.arraycopy(queue, 0, newQueue, 0, queue.length);
+ queue = newQueue;
+ }
+
// Queue Methods
+
+
/**
* 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.
+ * @throws NullPointerException if the specified element is null.
*/
- public boolean offer(E element) {
- if (element == null)
+ public boolean offer(E o) {
+ if (o == null)
throw new NullPointerException();
modCount++;
++size;
// Grow backing store if necessary
- while (size >= queue.length) {
- Object[] newQueue = new Object[2 * queue.length];
- System.arraycopy(queue, 0, newQueue, 0, queue.length);
- queue = newQueue;
- }
+ if (size >= queue.length)
+ grow(size);
- queue[size] = element;
+ queue[size] = o;
fixUp(size);
return true;
}
@@ -193,22 +309,33 @@ public class PriorityQueue extends Ab
return (E) queue[1];
}
- // Collection Methods
-
- // these first two override just to get the throws docs
+ // Collection Methods - the first two override to update docs
/**
- * @throws NullPointerException if the specified element is null.
+ * Adds the specified element to this queue.
+ * @return true (as per the general contract of
+ * Collection.add).
+ *
+ * @throws NullPointerException {@inheritDoc}
* @throws ClassCastException if the specified element cannot be compared
* with elements currently in the priority queue according
* to the priority queue's ordering.
*/
- public boolean add(E element) {
- return super.add(element);
+ public boolean add(E o) {
+ return super.add(o);
}
+
/**
- * @throws NullPointerException if any element is null.
+ * Adds all of the elements in the specified collection to this queue.
+ * The behavior of this operation is undefined if
+ * the specified collection is modified while the operation is in
+ * progress. (This implies that the behavior of this call is undefined if
+ * the specified collection is this queue, and this queue is nonempty.)
+ *
+ * This implementation iterates over the specified collection, and adds
+ * each object returned by the iterator to this collection, in turn.
+ * @throws NullPointerException {@inheritDoc}
* @throws ClassCastException if any element cannot be compared
* with elements currently in the priority queue according
* to the priority queue's ordering.
@@ -217,6 +344,21 @@ public class PriorityQueue extends Ab
return super.addAll(c);
}
+
+ /**
+ * Removes a single instance of the specified element from this
+ * queue, if it is present. More formally,
+ * removes an element e such that (o==null ? e==null :
+ * o.equals(e)), if the queue contains one or more such
+ * elements. Returns true if the queue contained the
+ * specified element (or equivalently, if the queue changed as a
+ * result of the call).
+ *
+ * This implementation iterates over the queue looking for the
+ * specified element. If it finds the element, it removes the element
+ * from the queue using the iterator's remove method.
+ *
+ */
public boolean remove(Object o) {
if (o == null)
return false;
@@ -239,6 +381,12 @@ public class PriorityQueue extends Ab
return false;
}
+ /**
+ * 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();
}
@@ -283,8 +431,7 @@ public class PriorityQueue extends Ab
checkForComodification();
PriorityQueue.this.remove(lastRet);
- if (lastRet < cursor)
- cursor--;
+ cursor--;
lastRet = 0;
expectedModCount = modCount;
}
@@ -295,11 +442,6 @@ 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;
}
@@ -321,8 +463,6 @@ public class PriorityQueue extends Ab
* 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?
*/
private E remove(int i) {
assert i <= size;
@@ -377,7 +517,7 @@ public class PriorityQueue extends Ab
private void fixDown(int k) {
int j;
if (comparator == null) {
- while ((j = k << 1) <= size) {
+ 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((E)queue[j]) <= 0)
@@ -386,7 +526,7 @@ public class PriorityQueue extends Ab
k = j;
}
} else {
- while ((j = k << 1) <= size) {
+ while ((j = k << 1) <= size && (j > 0)) {
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)
@@ -397,6 +537,15 @@ public class PriorityQueue extends Ab
}
}
+
+ /**
+ * Returns the comparator used to order this collection, or null
+ * if this collection is sorted according to its elements natural ordering
+ * (using Comparable).
+ *
+ * @return the comparator used to order this collection, or null
+ * if this collection is sorted according to its elements natural ordering.
+ */
public Comparator super E> comparator() {
return comparator;
}
@@ -410,7 +559,7 @@ 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();
@@ -428,7 +577,7 @@ public class PriorityQueue extends Ab
* 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();