--- jsr166/src/main/java/util/PriorityQueue.java	2003/08/05 12:11:08	1.22
+++ jsr166/src/main/java/util/PriorityQueue.java	2003/09/07 15:06:19	1.39
@@ -1,17 +1,22 @@
- package java.util;
+/*
+ * %W% %E%
+ *
+ * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
+ * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
+ */
+
+package java.util;
 
 /**
- * An unbounded 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 <i>natural order</i> (see {@link Comparable}), or
- * according to a {@link java.util.Comparator}, depending on which
- * constructor is used.
+ * 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 either according to
+ * their <i>natural order</i> (see {@link Comparable}), or according to a
+ * {@link java.util.Comparator}, depending on which constructor is used.
  * <p>The <em>head</em> of this queue is the <em>least</em> 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
+ * 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
  * <tt>null</tt> elements.
  *
  * <p>The {@link #remove()} and {@link #poll()} methods remove and
@@ -27,6 +32,18 @@
  * elements are added to a priority queue, its capacity grows
  * automatically.  The details of the growth policy are not specified.
  *
+ * <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
+ * guaranteed to traverse the elements of the PriorityQueue in any
+ * particular order. If you need ordered traversal, consider using
+ * <tt>Arrays.sort(pq.toArray())</tt>.
+ *
+ * <p> <strong>Note that this implementation is not synchronized.</strong>
+ * Multiple threads should not access a <tt>PriorityQueue</tt>
+ * instance concurrently if any of the threads modifies the list
+ * structurally. Instead, use the thread-safe {@link
+ * java.util.concurrent.PriorityBlockingQueue} class.
+ *
+ * 
  * <p>Implementation note: this implementation provides O(log(n)) time
  * for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
  * <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
@@ -38,11 +55,14 @@
  * <a href="{@docRoot}/../guide/collections/index.html">
  * Java Collections Framework</a>.
  * @since 1.5
+ * @version %I%, %G%
  * @author Josh Bloch
  */
 public class PriorityQueue<E> extends AbstractQueue<E>
     implements Queue<E>, java.io.Serializable {
 
+    private static final long serialVersionUID = -7720805057305804111L;
+
     private static final int DEFAULT_INITIAL_CAPACITY = 11;
 
     /**
@@ -80,7 +100,7 @@ public class PriorityQueue<E> extends Ab
     /**
      * Creates a <tt>PriorityQueue</tt> with the default initial capacity
      * (11) that orders its elements according to their natural
-     * ordering (using <tt>Comparable</tt>.)
+     * ordering (using <tt>Comparable</tt>).
      */
     public PriorityQueue() {
         this(DEFAULT_INITIAL_CAPACITY, null);
@@ -89,9 +109,11 @@ public class PriorityQueue<E> extends Ab
     /**
      * Creates a <tt>PriorityQueue</tt> with the specified initial capacity
      * that orders its elements according to their natural ordering
-     * (using <tt>Comparable</tt>.)
+     * (using <tt>Comparable</tt>).
      *
      * @param initialCapacity the initial capacity for this priority queue.
+     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
+     * than 1
      */
     public PriorityQueue(int initialCapacity) {
         this(initialCapacity, null);
@@ -108,7 +130,8 @@ public class PriorityQueue<E> extends Ab
      * @throws IllegalArgumentException if <tt>initialCapacity</tt> 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];
@@ -132,22 +155,22 @@ public class PriorityQueue<E> extends Ab
     /**
      * 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.
+     * case we can just place the elements in the order presented.
      */
     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.
+     * Initially fill elements of the queue array that is not to our knowledge
+     * sorted, so we must rearrange the elements to guarantee the heap
+     * invariant.
      */
     private void fillFromUnsorted(Collection<? extends E> c) {
         for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
-            add(i.next());
+            queue[++size] = i.next();
+        heapify();
     }
 
     /**
@@ -155,7 +178,7 @@ public class PriorityQueue<E> extends Ab
      * 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 SortedSet} or is another
+     * instance of a {@link java.util.SortedSet} or is another
      * <tt>PriorityQueue</tt>, 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
@@ -172,17 +195,16 @@ public class PriorityQueue<E> extends Ab
      */
     public PriorityQueue(Collection<? extends E> c) {
         initializeArray(c);
-        if (c instanceof SortedSet<? extends E>) {
-            SortedSet<? extends E> s = (SortedSet<? extends E>) 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<? extends E>) {
+        } else if (c instanceof PriorityQueue) {
             PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
             comparator = (Comparator<? super E>)s.comparator();
             fillFromSorted(s);
-        }
-        else {
+        } else {
             comparator = null;
             fillFromUnsorted(c);
         }
@@ -254,6 +276,7 @@ public class PriorityQueue<E> extends Ab
         queue = newQueue;
     }
             
+
     // Queue Methods
 
     /**
@@ -283,19 +306,21 @@ public class PriorityQueue<E> extends Ab
     public E poll() {
         if (size == 0)
             return null;
-        return (E) remove(1);
+        return remove();
     }
 
     public E peek() {
         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 <tt>null</tt>.
+     * Adds the specified element to this queue.
+     * @return <tt>true</tt> (as per the general contract of
+     * <tt>Collection.add</tt>).
+     *
+     * @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.
@@ -304,17 +329,40 @@ public class PriorityQueue<E> extends Ab
         return super.add(o);
     }
 
+   
     /**
+     * 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.)
+     * <p>
+     * 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.
-     * @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
-     * is <tt>null</tt>
      */
     public boolean addAll(Collection<? extends E> c) {
         return super.addAll(c);
     }
 
+
+    /**
+     * Removes a single instance of the specified element from this
+     * queue, if it is present.  More formally,
+     * removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
+     * o.equals(e))</tt>, if the queue contains one or more such
+     * elements.  Returns <tt>true</tt> if the queue contained the
+     * specified element (or equivalently, if the queue changed as a
+     * result of the call).
+     *
+     * <p>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.<p>
+     *
+     */
     public boolean remove(Object o) {
         if (o == null)
             return false;
@@ -322,14 +370,14 @@ public class PriorityQueue<E> extends Ab
         if (comparator == null) {
             for (int i = 1; i <= size; i++) {
                 if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
-                    remove(i);
+                    removeAt(i);
                     return true;
                 }
             }
         } else {
             for (int i = 1; i <= size; i++) {
                 if (comparator.compare((E)queue[i], (E)o) == 0) {
-                    remove(i);
+                    removeAt(i);
                     return true;
                 }
             }
@@ -337,11 +385,18 @@ public class PriorityQueue<E> 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<E> iterator() {
         return new Itr();
     }
 
     private class Itr implements Iterator<E> {
+
         /**
          * Index (into queue array) of element to be returned by
          * subsequent call to next.
@@ -349,9 +404,9 @@ public class PriorityQueue<E> extends Ab
         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.
+         * Index of element returned by most recent call to next,
+         * unless that element came from the forgetMeNot list.
+         * Reset to 0 if element is deleted by a call to remove.
          */
         private int lastRet = 0;
 
@@ -362,28 +417,69 @@ public class PriorityQueue<E> extends Ab
          */
         private int expectedModCount = modCount;
 
+        /**
+         * A list 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 fixup instead of a fixdown.)  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 ArrayList<E> forgetMeNot = null;
+
+        /**
+         * Element returned by the most recent call to next iff that
+         * element was drawn from the forgetMeNot list.
+         */
+        private Object lastRetElt = null;
+
         public boolean hasNext() {
-            return cursor <= size;
+            return cursor <= size || forgetMeNot != null;
         }
 
         public E next() {
             checkForComodification();
-            if (cursor > size)
+            E result;
+            if (cursor <= size) {
+                result = (E) queue[cursor];
+                lastRet = cursor++;
+            }
+            else if (forgetMeNot == null)
                 throw new NoSuchElementException();
-            E result = (E) queue[cursor];
-            lastRet = cursor++;
+            else {
+                int remaining = forgetMeNot.size();
+                result = forgetMeNot.remove(remaining - 1);
+                if (remaining == 1) 
+                    forgetMeNot = null;
+                lastRet = 0;
+                lastRetElt = result;
+            }
             return result;
         }
 
         public void remove() {
-            if (lastRet == 0)
-                throw new IllegalStateException();
             checkForComodification();
 
-            PriorityQueue.this.remove(lastRet);
-            if (lastRet < cursor)
-                cursor--;
-            lastRet = 0;
+            if (lastRet != 0) {
+                E moved = PriorityQueue.this.removeAt(lastRet);
+                lastRet = 0;
+                if (moved == null) {
+                    cursor--;
+                } else {
+                    if (forgetMeNot == null)
+                        forgetMeNot = new ArrayList<E>();
+                    forgetMeNot.add(moved);
+                }
+            } else if (lastRetElt != null) {
+                PriorityQueue.this.remove(lastRetElt);
+                lastRetElt = null;
+            } else {
+                throw new IllegalStateException();
+            }
+
             expectedModCount = modCount;
         }
 
@@ -393,11 +489,6 @@ public class PriorityQueue<E> 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;
     }
@@ -416,22 +507,51 @@ public class PriorityQueue<E> extends Ab
     }
 
     /**
-     * Removes and returns the ith element from queue.  Recall
-     * that queue is one-based, so 1 <= i <= size.
+     * Removes and returns the first element from queue.
+     */
+    public E remove() {
+        if (size == 0)
+            throw new NoSuchElementException();
+        modCount++;
+
+        E result = (E) queue[1];
+        queue[1] = queue[size];
+        queue[size--] = null;  // Drop extra ref to prevent memory leak
+        if (size > 1)
+            fixDown(1);
+
+        return result;
+    }
+
+    /**
+     * 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?
+     * Normally this method leaves the elements at positions from 1 up to i-1,
+     * inclusive, untouched.  Under these circumstances, it returns null.
+     * Occasionally, in order to maintain the heap invariant, it must move
+     * the last element of the list to some index in the range [2, i-1],
+     * and move the element previously at position (i/2) to position i.
+     * Under these circumstances, this method returns the element that was
+     * previously at the end of the list and is now at some position between
+     * 2 and i-1 inclusive.
      */
-    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];
+        E moved = (E) queue[size];
+        queue[i] = moved;
         queue[size--] = null;  // Drop extra ref to prevent memory leak
-        if (i <= size)
+        if (i <= size) {
             fixDown(i);
-        return result;
+            if (queue[i] == moved) {
+                fixUp(i);
+                if (queue[i] != moved)
+                    return moved;
+            }
+        }
+        return null;
     }
 
     /**
@@ -454,7 +574,7 @@ public class PriorityQueue<E> extends Ab
             }
         } else {
             while (k > 1) {
-                int j = 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;
@@ -475,17 +595,20 @@ public class PriorityQueue<E> extends Ab
     private void fixDown(int k) {
         int j;
         if (comparator == null) {
-            while ((j = k << 1) <= size) {
-                if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
+            while ((j = k << 1) <= size && (j > 0)) {
+                if (j<size && 
+                    ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
                     j++; // j indexes smallest kid
+
                 if (((Comparable<E>)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)
+            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)
                     break;
@@ -495,6 +618,23 @@ public class PriorityQueue<E> extends Ab
         }
     }
 
+    /**
+     * 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/2; i >= 1; i--)
+            fixDown(i);
+    }
+
+    /**
+     * Returns the comparator used to order this collection, or <tt>null</tt>
+     * if this collection is sorted according to its elements natural ordering
+     * (using <tt>Comparable</tt>).
+     *
+     * @return the comparator used to order this collection, or <tt>null</tt>
+     * if this collection is sorted according to its elements natural ordering.
+     */
     public Comparator<? super E> comparator() {
         return comparator;
     }
@@ -517,7 +657,7 @@ public class PriorityQueue<E> extends Ab
         s.writeInt(queue.length);
 
         // Write out all elements in the proper order.
-        for (int i=0; i<size; i++)
+        for (int i=1; i<=size; i++)
             s.writeObject(queue[i]);
     }
 
@@ -536,9 +676,8 @@ public class PriorityQueue<E> extends Ab
         queue = new Object[arrayLength];
 
         // Read in all elements in the proper order.
-        for (int i=0; i<size; i++)
-            queue[i] = s.readObject();
+        for (int i=1; i<=size; i++)
+            queue[i] = (E) s.readObject();
     }
 
 }
-