java/util/PriorityQueue.java

 package java.util;

/**
 * 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
 * <tt>null</tt> elements.
 *
 * <p>The {@link #remove()} and {@link #poll()} methods remove and
 * return the head of the queue.
 *
 * <p>The {@link #element()} and {@link #peek()} methods return, but do
 * not delete, the head of the queue.
 *
 * <p>A priority queue has a <i>capacity</i>.  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.
 *
 * <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
 * <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
 * constant time for the retrieval methods (<tt>peek</tt>,
 * <tt>element</tt>, and <tt>size</tt>).
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 * @since 1.5
 * @author Josh Bloch
 */
public class PriorityQueue<E> extends AbstractQueue<E>
    implements Queue<E>, 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 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.)
     *
     * queue.length must be >= 2, even if size == 0.
     */
    private transient Object[] queue;

    /**
     * The number of elements in the priority queue.
     */
    private int size = 0;

    /**
     * The comparator, or null if priority queue uses elements'
     * natural ordering.
     */
    private final Comparator<? super E> comparator;

    /**
     * The number of times this priority queue has been
     * <i>structurally modified</i>.  See AbstractList for gory details.
     */
    private transient int modCount = 0;

    /**
     * Creates a <tt>PriorityQueue</tt> with the default initial capacity
     * (11) that orders its elements according to their natural
     * ordering (using <tt>Comparable</tt>.)
     */
    public PriorityQueue() {
        this(DEFAULT_INITIAL_CAPACITY, null);
    }

    /**
     * Creates a <tt>PriorityQueue</tt> with the specified initial capacity
     * that orders its elements according to their natural ordering
     * (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);
    }

    /**
     * Creates a <tt>PriorityQueue</tt> 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 <tt>null</tt> then the order depends on the elements' natural
     * ordering.
     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
     * than 1
     */
    public PriorityQueue(int initialCapacity, 
                         Comparator<? super E> comparator) {
        if (initialCapacity < 1)
            throw new IllegalArgumentException();
        this.queue = new Object[initialCapacity + 1];
        this.comparator = comparator;
    }

    /**
     * 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 <tt>PriorityQueue</tt> 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 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
     * 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.
     * @throws ClassCastException if elements of the specified collection
     *         cannot be compared to one another according to the priority
     *         queue's ordering.
     * @throws NullPointerException if <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    public PriorityQueue(Collection<? extends E> c) {
        initializeArray(c);
        if (c instanceof SortedSet<? extends E>) {
            SortedSet<? extends E> s = (SortedSet<? extends E>) c;
            comparator = (Comparator<? super E>)s.comparator();
            fillFromSorted(s);
        }
        else if (c instanceof PriorityQueue<? extends E>) {
            PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
            comparator = (Comparator<? super E>)s.comparator();
            fillFromSorted(s);
        }
        else {
            comparator = null;
            fillFromUnsorted(c);
        }
    }

    /**
     * Creates a <tt>PriorityQueue</tt> 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 <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    public PriorityQueue(PriorityQueue<? extends E> c) {
        initializeArray(c);
        comparator = (Comparator<? super E>)c.comparator();
        fillFromSorted(c);
    }

    /**
     * Creates a <tt>PriorityQueue</tt> 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 <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    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.
     *
     * @return <tt>true</tt>
     * @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 <tt>null</tt>.
     */
    public boolean offer(E o) {
        if (o == null)
            throw new NullPointerException();
        modCount++;
        ++size;

        // Grow backing store if necessary
        if (size >= queue.length) 
            grow(size);

        queue[size] = o;
        fixUp(size);
        return true;
    }

    public E poll() {
        if (size == 0)
            return null;
        return (E) remove(1);
    }

    public E peek() {
        return (E) queue[1];
    }

    // Collection Methods - the first two override to update docs

    /**
     * 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.
     */
    public boolean add(E o) {
        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.
     */
    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;

        if (comparator == null) {
            for (int i = 1; i <= size; i++) {
                if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
                    remove(i);
                    return true;
                }
            }
        } else {
            for (int i = 1; i <= size; i++) {
                if (comparator.compare((E)queue[i], (E)o) == 0) {
                    remove(i);
                    return true;
                }
            }
        }
        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.
         */
        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.
         */
        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.
         */
        private int expectedModCount = modCount;

        public boolean hasNext() {
            return cursor <= size;
        }

        public E next() {
            checkForComodification();
            if (cursor > size)
                throw new NoSuchElementException();
            E result = (E) queue[cursor];
            lastRet = cursor++;
            return result;
        }

        public void remove() {
            if (lastRet == 0)
                throw new IllegalStateException();
            checkForComodification();

            PriorityQueue.this.remove(lastRet);
            if (lastRet < cursor)
                cursor--;
            lastRet = 0;
            expectedModCount = modCount;
        }

        final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }
    }

    public int size() {
        return size;
    }

    /**
     * Remove all elements from the priority queue.
     */
    public void clear() {
        modCount++;

        // Null out element references to prevent memory leak
        for (int i=1; i<=size; i++)
            queue[i] = null;

        size = 0;
    }

    /**
     * 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;
        modCount++;

        E result = (E) queue[i];
        queue[i] = queue[size];
        queue[size--] = null;  // Drop extra ref to prevent memory leak
        if (i <= size)
            fixDown(i);
        return result;
    }

    /**
     * Establishes the heap invariant (described above) assuming the heap
     * satisfies the invariant except possibly for the leaf-node indexed by k
     * (which may have a nextExecutionTime less than its parent's).
     *
     * This method functions by "promoting" queue[k] up the hierarchy
     * (by swapping it with its parent) repeatedly until queue[k]
     * is greater than or equal to its parent.
     */
    private void fixUp(int k) {
        if (comparator == null) {
            while (k > 1) {
                int j = k >> 1;
                if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
                    break;
                Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
                k = j;
            }
        } else {
            while (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;
                k = j;
            }
        }
    }

    /**
     * Establishes the heap invariant (described above) in the subtree
     * rooted at k, which is assumed to satisfy the heap invariant except
     * possibly for node k itself (which may be greater than its children).
     *
     * This method functions by "demoting" queue[k] down the hierarchy
     * (by swapping it with its smaller child) repeatedly until queue[k]
     * is less than or equal to its children.
     */
    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)
                    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)
                    j++; // j indexes smallest kid
                if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
                    break;
                Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
                k = j;
            }
        }
    }


    /**
     * 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;
    }

    /**
     * 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
     * <tt>Object</tt>) in the proper order.
     * @param s the stream
     */
    private 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; i<size; i++)
            s.writeObject(queue[i]);
    }

    /**
     * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
     * deserialize it).
     * @param s the stream
     */
    private 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 Object[arrayLength];

        // Read in all elements in the proper order.
        for (int i=0; i<size; i++)
            queue[i] = s.readObject();
    }

}

Revision:	1.23
Committed:	Wed Aug 6 01:57:53 2003 UTC (20 years, 9 months ago) by dholmes
Branch:	MAIN
Changes since 1.22:	+54 -13 lines
Log Message:	Final major updates to Collection related classes.
#	User	Rev	Content
1	tim	1.2	package java.util;
2	tim	1.1
3			/**
4	dholmes	1.23	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
5			* This queue orders
6	brian	1.6	* elements according to an order specified at construction time, which is
7	tim	1.19	* specified in the same manner as {@link java.util.TreeSet} and
8	dholmes	1.18	* {@link java.util.TreeMap}: elements are ordered
9	tim	1.2	* either according to their <i>natural order</i> (see {@link Comparable}), or
10	tim	1.19	* according to a {@link java.util.Comparator}, depending on which
11	dholmes	1.18	* constructor is used.
12	tim	1.19	* <p>The <em>head</em> of this queue is the <em>least</em> element with
13			* respect to the specified ordering.
14	dholmes	1.18	* If multiple elements are tied for least value, the
15	tim	1.14	* head is one of those elements. A priority queue does not permit
16	dholmes	1.11	* <tt>null</tt> elements.
17	tim	1.14	*
18	dholmes	1.11	* <p>The {@link #remove()} and {@link #poll()} methods remove and
19			* return the head of the queue.
20			*
21			* <p>The {@link #element()} and {@link #peek()} methods return, but do
22			* not delete, the head of the queue.
23	tim	1.2	*
24	dl	1.7	* <p>A priority queue has a <i>capacity</i>. The capacity is the
25			* size of the array used internally to store the elements on the
26	dholmes	1.20	* queue.
27	dholmes	1.18	* It is always at least as large as the queue size. As
28	dl	1.7	* elements are added to a priority queue, its capacity grows
29			* automatically. The details of the growth policy are not specified.
30	tim	1.2	*
31	dholmes	1.11	* <p>Implementation note: this implementation provides O(log(n)) time
32			* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
33			* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
34			* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
35			* constant time for the retrieval methods (<tt>peek</tt>,
36			* <tt>element</tt>, and <tt>size</tt>).
37	tim	1.2	*
38			* <p>This class is a member of the
39			* <a href="{@docRoot}/../guide/collections/index.html">
40			* Java Collections Framework</a>.
41	dl	1.7	* @since 1.5
42			* @author Josh Bloch
43	tim	1.2	*/
44			public class PriorityQueue<E> extends AbstractQueue<E>
45	dl	1.22	implements Queue<E>, java.io.Serializable {
46	dholmes	1.11
47	tim	1.2	private static final int DEFAULT_INITIAL_CAPACITY = 11;
48	tim	1.1
49	tim	1.2	/**
50			* Priority queue represented as a balanced binary heap: the two children
51			* of queue[n] are queue[2n] and queue[2n + 1]. The priority queue is
52			* ordered by comparator, or by the elements' natural ordering, if
53	brian	1.6	* comparator is null: For each node n in the heap and each descendant d
54			* of n, n <= d.
55	tim	1.2	*
56	brian	1.6	* The element with the lowest value is in queue[1], assuming the queue is
57			* nonempty. (A one-based array is used in preference to the traditional
58			* zero-based array to simplify parent and child calculations.)
59	tim	1.2	*
60			* queue.length must be >= 2, even if size == 0.
61			*/
62	tim	1.16	private transient Object[] queue;
63	tim	1.1
64	tim	1.2	/**
65			* The number of elements in the priority queue.
66			*/
67			private int size = 0;
68	tim	1.1
69	tim	1.2	/**
70			* The comparator, or null if priority queue uses elements'
71			* natural ordering.
72			*/
73	tim	1.16	private final Comparator<? super E> comparator;
74	tim	1.2
75			/**
76			* The number of times this priority queue has been
77			* <i>structurally modified</i>. See AbstractList for gory details.
78			*/
79	dl	1.5	private transient int modCount = 0;
80	tim	1.2
81			/**
82	dholmes	1.21	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
83	dl	1.7	* (11) that orders its elements according to their natural
84			* ordering (using <tt>Comparable</tt>.)
85	tim	1.2	*/
86			public PriorityQueue() {
87	dholmes	1.11	this(DEFAULT_INITIAL_CAPACITY, null);
88	tim	1.1	}
89	tim	1.2
90			/**
91	dholmes	1.21	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
92	dl	1.7	* that orders its elements according to their natural ordering
93			* (using <tt>Comparable</tt>.)
94	tim	1.2	*
95			* @param initialCapacity the initial capacity for this priority queue.
96	dholmes	1.23	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
97			* than 1
98	tim	1.2	*/
99			public PriorityQueue(int initialCapacity) {
100			this(initialCapacity, null);
101	tim	1.1	}
102	tim	1.2
103			/**
104	dholmes	1.21	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
105	tim	1.2	* that orders its elements according to the specified comparator.
106			*
107			* @param initialCapacity the initial capacity for this priority queue.
108			* @param comparator the comparator used to order this priority queue.
109	dholmes	1.11	* If <tt>null</tt> then the order depends on the elements' natural
110			* ordering.
111	dholmes	1.15	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
112			* than 1
113	tim	1.2	*/
114	dholmes	1.23	public PriorityQueue(int initialCapacity,
115			Comparator<? super E> comparator) {
116	tim	1.2	if (initialCapacity < 1)
117	dholmes	1.15	throw new IllegalArgumentException();
118	tim	1.16	this.queue = new Object[initialCapacity + 1];
119	tim	1.2	this.comparator = comparator;
120	tim	1.1	}
121
122	tim	1.2	/**
123	dl	1.22	* Common code to initialize underlying queue array across
124			* constructors below.
125			*/
126			private void initializeArray(Collection<? extends E> c) {
127			int sz = c.size();
128			int initialCapacity = (int)Math.min((sz * 110L) / 100,
129			Integer.MAX_VALUE - 1);
130			if (initialCapacity < 1)
131			initialCapacity = 1;
132
133			this.queue = new Object[initialCapacity + 1];
134			}
135
136			/**
137			* Initially fill elements of the queue array under the
138			* knowledge that it is sorted or is another PQ, in which
139			* case we can just place the elements without fixups.
140			*/
141			private void fillFromSorted(Collection<? extends E> c) {
142			for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
143			queue[++size] = i.next();
144			}
145
146
147			/**
148			* Initially fill elements of the queue array that is
149			* not to our knowledge sorted, so we must add them
150			* one by one.
151			*/
152			private void fillFromUnsorted(Collection<? extends E> c) {
153			for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
154			add(i.next());
155			}
156
157			/**
158			* Creates a <tt>PriorityQueue</tt> containing the elements in the
159			* specified collection. The priority queue has an initial
160			* capacity of 110% of the size of the specified collection or 1
161			* if the collection is empty. If the specified collection is an
162			* instance of a {@link SortedSet} or is another
163			* <tt>PriorityQueue</tt>, the priority queue will be sorted
164			* according to the same comparator, or according to its elements'
165			* natural order if the collection is sorted according to its
166			* elements' natural order. Otherwise, the priority queue is
167			* ordered according to its elements' natural order.
168	tim	1.2	*
169	dholmes	1.15	* @param c the collection whose elements are to be placed
170	tim	1.2	* into this priority queue.
171			* @throws ClassCastException if elements of the specified collection
172			* cannot be compared to one another according to the priority
173			* queue's ordering.
174	dholmes	1.15	* @throws NullPointerException if <tt>c</tt> or any element within it
175			* is <tt>null</tt>
176	tim	1.2	*/
177	tim	1.16	public PriorityQueue(Collection<? extends E> c) {
178	dl	1.22	initializeArray(c);
179			if (c instanceof SortedSet<? extends E>) {
180			SortedSet<? extends E> s = (SortedSet<? extends E>) c;
181			comparator = (Comparator<? super E>)s.comparator();
182			fillFromSorted(s);
183			}
184			else if (c instanceof PriorityQueue<? extends E>) {
185			PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
186			comparator = (Comparator<? super E>)s.comparator();
187			fillFromSorted(s);
188			}
189			else {
190	tim	1.2	comparator = null;
191	dl	1.22	fillFromUnsorted(c);
192	tim	1.2	}
193	dl	1.22	}
194
195			/**
196			* Creates a <tt>PriorityQueue</tt> containing the elements in the
197			* specified collection. The priority queue has an initial
198			* capacity of 110% of the size of the specified collection or 1
199			* if the collection is empty. This priority queue will be sorted
200			* according to the same comparator as the given collection, or
201			* according to its elements' natural order if the collection is
202			* sorted according to its elements' natural order.
203			*
204			* @param c the collection whose elements are to be placed
205			* into this priority queue.
206			* @throws ClassCastException if elements of the specified collection
207			* cannot be compared to one another according to the priority
208			* queue's ordering.
209			* @throws NullPointerException if <tt>c</tt> or any element within it
210			* is <tt>null</tt>
211			*/
212			public PriorityQueue(PriorityQueue<? extends E> c) {
213			initializeArray(c);
214			comparator = (Comparator<? super E>)c.comparator();
215			fillFromSorted(c);
216			}
217	dholmes	1.18
218	dl	1.22	/**
219			* Creates a <tt>PriorityQueue</tt> containing the elements in the
220			* specified collection. The priority queue has an initial
221			* capacity of 110% of the size of the specified collection or 1
222			* if the collection is empty. This priority queue will be sorted
223			* according to the same comparator as the given collection, or
224			* according to its elements' natural order if the collection is
225			* sorted according to its elements' natural order.
226			*
227			* @param c the collection whose elements are to be placed
228			* into this priority queue.
229			* @throws ClassCastException if elements of the specified collection
230			* cannot be compared to one another according to the priority
231			* queue's ordering.
232			* @throws NullPointerException if <tt>c</tt> or any element within it
233			* is <tt>null</tt>
234			*/
235			public PriorityQueue(SortedSet<? extends E> c) {
236			initializeArray(c);
237			comparator = (Comparator<? super E>)c.comparator();
238			fillFromSorted(c);
239	tim	1.1	}
240
241	dl	1.22	/**
242			* Resize array, if necessary, to be able to hold given index
243			*/
244			private void grow(int index) {
245			int newlen = queue.length;
246			if (index < newlen) // don't need to grow
247			return;
248			if (index == Integer.MAX_VALUE)
249			throw new OutOfMemoryError();
250			while (newlen <= index) {
251			if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow
252			newlen = Integer.MAX_VALUE;
253			else
254			newlen <<= 2;
255			}
256			Object[] newQueue = new Object[newlen];
257			System.arraycopy(queue, 0, newQueue, 0, queue.length);
258			queue = newQueue;
259			}
260
261	tim	1.2	// Queue Methods
262
263	dholmes	1.23
264
265	tim	1.2	/**
266	dholmes	1.11	* Add the specified element to this priority queue.
267	tim	1.2	*
268	dholmes	1.11	* @return <tt>true</tt>
269			* @throws ClassCastException if the specified element cannot be compared
270			* with elements currently in the priority queue according
271			* to the priority queue's ordering.
272	dholmes	1.18	* @throws NullPointerException if the specified element is <tt>null</tt>.
273	tim	1.2	*/
274	dholmes	1.18	public boolean offer(E o) {
275			if (o == null)
276	dholmes	1.11	throw new NullPointerException();
277			modCount++;
278			++size;
279
280			// Grow backing store if necessary
281	dl	1.22	if (size >= queue.length)
282			grow(size);
283	dholmes	1.11
284	dholmes	1.18	queue[size] = o;
285	dholmes	1.11	fixUp(size);
286			return true;
287			}
288
289	tim	1.1	public E poll() {
290	tim	1.2	if (size == 0)
291			return null;
292	tim	1.16	return (E) remove(1);
293	tim	1.1	}
294	tim	1.2
295	tim	1.1	public E peek() {
296	tim	1.16	return (E) queue[1];
297	tim	1.1	}
298
299	dholmes	1.23	// Collection Methods - the first two override to update docs
300	dholmes	1.11
301			/**
302	dholmes	1.23	* Adds the specified element to this queue.
303			* @return <tt>true</tt> (as per the general contract of
304			* <tt>Collection.add</tt>).
305			*
306			* @throws NullPointerException {@inheritDoc}
307	dholmes	1.15	* @throws ClassCastException if the specified element cannot be compared
308			* with elements currently in the priority queue according
309			* to the priority queue's ordering.
310	dholmes	1.11	*/
311	dholmes	1.18	public boolean add(E o) {
312			return super.add(o);
313	dholmes	1.11	}
314
315	dholmes	1.23
316	tim	1.14	/**
317	dholmes	1.23	* Adds all of the elements in the specified collection to this queue.
318			* The behavior of this operation is undefined if
319			* the specified collection is modified while the operation is in
320			* progress. (This implies that the behavior of this call is undefined if
321			* the specified collection is this queue, and this queue is nonempty.)
322			* <p>
323			* This implementation iterates over the specified collection, and adds
324			* each object returned by the iterator to this collection, in turn.
325			* @throws NullPointerException {@inheritDoc}
326	dholmes	1.15	* @throws ClassCastException if any element cannot be compared
327			* with elements currently in the priority queue according
328			* to the priority queue's ordering.
329	tim	1.14	*/
330			public boolean addAll(Collection<? extends E> c) {
331			return super.addAll(c);
332			}
333	dholmes	1.11
334	dholmes	1.23
335			/**
336			* Removes a single instance of the specified element from this
337			* queue, if it is present. More formally,
338			* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
339			* o.equals(e))</tt>, if the queue contains one or more such
340			* elements. Returns <tt>true</tt> if the queue contained the
341			* specified element (or equivalently, if the queue changed as a
342			* result of the call).
343			*
344			* <p>This implementation iterates over the queue looking for the
345			* specified element. If it finds the element, it removes the element
346			* from the queue using the iterator's remove method.<p>
347			*
348			*/
349	dl	1.12	public boolean remove(Object o) {
350	dholmes	1.11	if (o == null)
351	dholmes	1.15	return false;
352	tim	1.2
353			if (comparator == null) {
354			for (int i = 1; i <= size; i++) {
355	tim	1.16	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
356	tim	1.2	remove(i);
357			return true;
358			}
359			}
360			} else {
361			for (int i = 1; i <= size; i++) {
362	tim	1.16	if (comparator.compare((E)queue[i], (E)o) == 0) {
363	tim	1.2	remove(i);
364			return true;
365			}
366			}
367			}
368	tim	1.1	return false;
369			}
370	tim	1.2
371	dholmes	1.23	/**
372			* Returns an iterator over the elements in this queue. The iterator
373			* does not return the elements in any particular order.
374			*
375			* @return an iterator over the elements in this queue.
376			*/
377	tim	1.2	public Iterator<E> iterator() {
378	dl	1.7	return new Itr();
379	tim	1.2	}
380
381			private class Itr implements Iterator<E> {
382	dl	1.7	/**
383			* Index (into queue array) of element to be returned by
384	tim	1.2	* subsequent call to next.
385	dl	1.7	*/
386			private int cursor = 1;
387	tim	1.2
388	dl	1.7	/**
389			* Index of element returned by most recent call to next or
390			* previous. Reset to 0 if this element is deleted by a call
391			* to remove.
392			*/
393			private int lastRet = 0;
394
395			/**
396			* The modCount value that the iterator believes that the backing
397			* List should have. If this expectation is violated, the iterator
398			* has detected concurrent modification.
399			*/
400			private int expectedModCount = modCount;
401	tim	1.2
402	dl	1.7	public boolean hasNext() {
403			return cursor <= size;
404			}
405
406			public E next() {
407	tim	1.2	checkForComodification();
408			if (cursor > size)
409	dl	1.7	throw new NoSuchElementException();
410	tim	1.16	E result = (E) queue[cursor];
411	tim	1.2	lastRet = cursor++;
412			return result;
413	dl	1.7	}
414	tim	1.2
415	dl	1.7	public void remove() {
416			if (lastRet == 0)
417			throw new IllegalStateException();
418	tim	1.2	checkForComodification();
419
420			PriorityQueue.this.remove(lastRet);
421			if (lastRet < cursor)
422			cursor--;
423			lastRet = 0;
424			expectedModCount = modCount;
425	dl	1.7	}
426	tim	1.2
427	dl	1.7	final void checkForComodification() {
428			if (modCount != expectedModCount)
429			throw new ConcurrentModificationException();
430			}
431	tim	1.2	}
432
433	tim	1.1	public int size() {
434	tim	1.2	return size;
435	tim	1.1	}
436	tim	1.2
437			/**
438			* Remove all elements from the priority queue.
439			*/
440			public void clear() {
441			modCount++;
442
443			// Null out element references to prevent memory leak
444			for (int i=1; i<=size; i++)
445			queue[i] = null;
446
447			size = 0;
448			}
449
450			/**
451			* Removes and returns the ith element from queue. Recall
452			* that queue is one-based, so 1 <= i <= size.
453			*
454			* XXX: Could further special-case i==size, but is it worth it?
455			* XXX: Could special-case i==0, but is it worth it?
456			*/
457			private E remove(int i) {
458			assert i <= size;
459			modCount++;
460
461	tim	1.16	E result = (E) queue[i];
462	tim	1.2	queue[i] = queue[size];
463			queue[size--] = null; // Drop extra ref to prevent memory leak
464			if (i <= size)
465			fixDown(i);
466			return result;
467	tim	1.1	}
468
469	tim	1.2	/**
470			* Establishes the heap invariant (described above) assuming the heap
471			* satisfies the invariant except possibly for the leaf-node indexed by k
472			* (which may have a nextExecutionTime less than its parent's).
473			*
474			* This method functions by "promoting" queue[k] up the hierarchy
475			* (by swapping it with its parent) repeatedly until queue[k]
476			* is greater than or equal to its parent.
477			*/
478			private void fixUp(int k) {
479			if (comparator == null) {
480			while (k > 1) {
481			int j = k >> 1;
482	tim	1.16	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
483	tim	1.2	break;
484	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
485	tim	1.2	k = j;
486			}
487			} else {
488			while (k > 1) {
489			int j = k >> 1;
490	tim	1.16	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
491	tim	1.2	break;
492	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
493	tim	1.2	k = j;
494			}
495			}
496			}
497
498			/**
499			* Establishes the heap invariant (described above) in the subtree
500			* rooted at k, which is assumed to satisfy the heap invariant except
501			* possibly for node k itself (which may be greater than its children).
502			*
503			* This method functions by "demoting" queue[k] down the hierarchy
504			* (by swapping it with its smaller child) repeatedly until queue[k]
505			* is less than or equal to its children.
506			*/
507			private void fixDown(int k) {
508			int j;
509			if (comparator == null) {
510			while ((j = k << 1) <= size) {
511	tim	1.16	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
512	tim	1.2	j++; // j indexes smallest kid
513	tim	1.16	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
514	tim	1.2	break;
515	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
516	tim	1.2	k = j;
517			}
518			} else {
519			while ((j = k << 1) <= size) {
520	tim	1.16	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
521	tim	1.2	j++; // j indexes smallest kid
522	tim	1.16	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
523	tim	1.2	break;
524	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
525	tim	1.2	k = j;
526			}
527			}
528			}
529
530	dholmes	1.23
531			/**
532			* Returns the comparator used to order this collection, or <tt>null</tt>
533			* if this collection is sorted according to its elements natural ordering
534			* (using <tt>Comparable</tt>.)
535			*
536			* @return the comparator used to order this collection, or <tt>null</tt>
537			* if this collection is sorted according to its elements natural ordering.
538			*/
539	tim	1.16	public Comparator<? super E> comparator() {
540	tim	1.2	return comparator;
541			}
542	dl	1.5
543			/**
544			* Save the state of the instance to a stream (that
545			* is, serialize it).
546			*
547			* @serialData The length of the array backing the instance is
548			* emitted (int), followed by all of its elements (each an
549			* <tt>Object</tt>) in the proper order.
550	dl	1.7	* @param s the stream
551	dl	1.5	*/
552	dl	1.22	private void writeObject(java.io.ObjectOutputStream s)
553	dl	1.5	throws java.io.IOException{
554	dl	1.7	// Write out element count, and any hidden stuff
555			s.defaultWriteObject();
556	dl	1.5
557			// Write out array length
558			s.writeInt(queue.length);
559
560	dl	1.7	// Write out all elements in the proper order.
561			for (int i=0; i<size; i++)
562	dl	1.5	s.writeObject(queue[i]);
563			}
564
565			/**
566			* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
567			* deserialize it).
568	dl	1.7	* @param s the stream
569	dl	1.5	*/
570	dl	1.22	private void readObject(java.io.ObjectInputStream s)
571	dl	1.5	throws java.io.IOException, ClassNotFoundException {
572	dl	1.7	// Read in size, and any hidden stuff
573			s.defaultReadObject();
574	dl	1.5
575			// Read in array length and allocate array
576			int arrayLength = s.readInt();
577	tim	1.16	queue = new Object[arrayLength];
578	dl	1.5
579	dl	1.7	// Read in all elements in the proper order.
580			for (int i=0; i<size; i++)
581	tim	1.16	queue[i] = s.readObject();
582	dl	1.5	}
583
584	tim	1.1	}
585	dholmes	1.11