java/util/PriorityQueue.java

 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.
 * The <em>head</em> 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
 * <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;

    /**
     * Create 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);
    }

    /**
     * Create 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.
     */
    public PriorityQueue(int initialCapacity) {
        this(initialCapacity, null);
    }

    /**
     * Create 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;
    }

    /**
     * Create 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
     * 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
     * <tt>Sorted</tt>, 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) {
        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();
        } else {
            comparator = null;
            for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
                add(i.next());
        }
    }

    // Queue Methods

    /**
     * Add the specified element to this priority queue.
     *
     * @param element the element to add.
     * @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 null.
     */
    public boolean offer(E element) {
        if (element == 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;
        }

        queue[size] = element;
        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

    // these first two override just to get the throws docs

    /**
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     * @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);
    }

    /**
     * @throws NullPointerException if any element is <tt>null</tt>.
     * @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);
    }

    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;
    }

    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();
        }
    }

    /**
     * Returns the number of elements in this priority queue.
     *
     * @return the number of elements in this priority queue.
     */
    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;
            }
        }
    }

    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 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; 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 synchronized void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in size, and any hidden stuff
        s.defaultReadObject();

        // Read in array length and allocate array
        int arrayLength = s.readInt();
        queue = new Object[arrayLength];

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

}

Revision:	1.17
Committed:	Thu Jul 31 19:49:42 2003 UTC (20 years, 9 months ago) by tim
Branch:	MAIN
Changes since 1.16:	+2 -2 lines
Log Message:	Fix broken doc links
#	User	Rev	Content
1	tim	1.2	package java.util;
2	tim	1.1
3			/**
4	tim	1.2	* An unbounded priority queue based on a priority heap. This queue orders
5	brian	1.6	* elements according to an order specified at construction time, which is
6	tim	1.17	* specified in the same manner as {@link java.util.TreeSet} and {@link java.util.TreeMap}:
7	dholmes	1.11	* elements are ordered
8	tim	1.2	* either according to their <i>natural order</i> (see {@link Comparable}), or
9	tim	1.17	* according to a {@link java.util.Comparator}, depending on which constructor is used.
10	dholmes	1.11	* The <em>head</em> of this queue is the least element with respect to the
11	tim	1.14	* specified ordering. If multiple elements are tied for least value, the
12			* head is one of those elements. A priority queue does not permit
13	dholmes	1.11	* <tt>null</tt> elements.
14	tim	1.14	*
15	dholmes	1.11	* <p>The {@link #remove()} and {@link #poll()} methods remove and
16			* return the head of the queue.
17			*
18			* <p>The {@link #element()} and {@link #peek()} methods return, but do
19			* not delete, the head of the queue.
20	tim	1.2	*
21	dl	1.7	* <p>A priority queue has a <i>capacity</i>. The capacity is the
22			* size of the array used internally to store the elements on the
23			* queue. It is always at least as large as the queue size. As
24			* elements are added to a priority queue, its capacity grows
25			* automatically. The details of the growth policy are not specified.
26	tim	1.2	*
27	dholmes	1.11	* <p>Implementation note: this implementation provides O(log(n)) time
28			* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
29			* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
30			* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
31			* constant time for the retrieval methods (<tt>peek</tt>,
32			* <tt>element</tt>, and <tt>size</tt>).
33	tim	1.2	*
34			* <p>This class is a member of the
35			* <a href="{@docRoot}/../guide/collections/index.html">
36			* Java Collections Framework</a>.
37	dl	1.7	* @since 1.5
38			* @author Josh Bloch
39	tim	1.2	*/
40			public class PriorityQueue<E> extends AbstractQueue<E>
41	dl	1.13	implements Queue<E>, java.io.Serializable {
42	dholmes	1.11
43	tim	1.2	private static final int DEFAULT_INITIAL_CAPACITY = 11;
44	tim	1.1
45	tim	1.2	/**
46			* Priority queue represented as a balanced binary heap: the two children
47			* of queue[n] are queue[2n] and queue[2n + 1]. The priority queue is
48			* ordered by comparator, or by the elements' natural ordering, if
49	brian	1.6	* comparator is null: For each node n in the heap and each descendant d
50			* of n, n <= d.
51	tim	1.2	*
52	brian	1.6	* The element with the lowest value is in queue[1], assuming the queue is
53			* nonempty. (A one-based array is used in preference to the traditional
54			* zero-based array to simplify parent and child calculations.)
55	tim	1.2	*
56			* queue.length must be >= 2, even if size == 0.
57			*/
58	tim	1.16	private transient Object[] queue;
59	tim	1.1
60	tim	1.2	/**
61			* The number of elements in the priority queue.
62			*/
63			private int size = 0;
64	tim	1.1
65	tim	1.2	/**
66			* The comparator, or null if priority queue uses elements'
67			* natural ordering.
68			*/
69	tim	1.16	private final Comparator<? super E> comparator;
70	tim	1.2
71			/**
72			* The number of times this priority queue has been
73			* <i>structurally modified</i>. See AbstractList for gory details.
74			*/
75	dl	1.5	private transient int modCount = 0;
76	tim	1.2
77			/**
78	dholmes	1.11	* Create a <tt>PriorityQueue</tt> with the default initial capacity
79	dl	1.7	* (11) that orders its elements according to their natural
80			* ordering (using <tt>Comparable</tt>.)
81	tim	1.2	*/
82			public PriorityQueue() {
83	dholmes	1.11	this(DEFAULT_INITIAL_CAPACITY, null);
84	tim	1.1	}
85	tim	1.2
86			/**
87	dholmes	1.11	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
88	dl	1.7	* that orders its elements according to their natural ordering
89			* (using <tt>Comparable</tt>.)
90	tim	1.2	*
91			* @param initialCapacity the initial capacity for this priority queue.
92			*/
93			public PriorityQueue(int initialCapacity) {
94			this(initialCapacity, null);
95	tim	1.1	}
96	tim	1.2
97			/**
98	dholmes	1.11	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
99	tim	1.2	* that orders its elements according to the specified comparator.
100			*
101			* @param initialCapacity the initial capacity for this priority queue.
102			* @param comparator the comparator used to order this priority queue.
103	dholmes	1.11	* If <tt>null</tt> then the order depends on the elements' natural
104			* ordering.
105	dholmes	1.15	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
106			* than 1
107	tim	1.2	*/
108	tim	1.16	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
109	tim	1.2	if (initialCapacity < 1)
110	dholmes	1.15	throw new IllegalArgumentException();
111	tim	1.16	this.queue = new Object[initialCapacity + 1];
112	tim	1.2	this.comparator = comparator;
113	tim	1.1	}
114
115	tim	1.2	/**
116	dholmes	1.11	* Create a <tt>PriorityQueue</tt> containing the elements in the specified
117	tim	1.2	* collection. The priority queue has an initial capacity of 110% of the
118	tim	1.16	* size of the specified collection; or 1 if the collection is empty.
119	dholmes	1.15	* If the specified collection
120	tim	1.2	* implements the {@link Sorted} interface, the priority queue will be
121			* sorted according to the same comparator, or according to its elements'
122			* natural order if the collection is sorted according to its elements'
123	brian	1.6	* natural order. If the specified collection does not implement
124			* <tt>Sorted</tt>, the priority queue is ordered according to
125	tim	1.2	* its elements' natural order.
126			*
127	dholmes	1.15	* @param c the collection whose elements are to be placed
128	tim	1.2	* into this priority queue.
129			* @throws ClassCastException if elements of the specified collection
130			* cannot be compared to one another according to the priority
131			* queue's ordering.
132	dholmes	1.15	* @throws NullPointerException if <tt>c</tt> or any element within it
133			* is <tt>null</tt>
134	tim	1.2	*/
135	tim	1.16	public PriorityQueue(Collection<? extends E> c) {
136	dholmes	1.15	int sz = c.size();
137	tim	1.2	int initialCapacity = (int)Math.min((sz * 110L) / 100,
138			Integer.MAX_VALUE - 1);
139			if (initialCapacity < 1)
140			initialCapacity = 1;
141	dholmes	1.15
142	tim	1.16	this.queue = new Object[initialCapacity + 1];
143	tim	1.2
144	dholmes	1.15	if (c instanceof Sorted) {
145			// FIXME: this code assumes too much
146	tim	1.16	this.comparator = (Comparator<? super E>) ((Sorted)c).comparator();
147			for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
148	tim	1.2	queue[++size] = i.next();
149			} else {
150			comparator = null;
151	tim	1.16	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
152	tim	1.2	add(i.next());
153			}
154	tim	1.1	}
155
156	tim	1.2	// Queue Methods
157
158			/**
159	dholmes	1.11	* Add the specified element to this priority queue.
160	tim	1.2	*
161	dholmes	1.11	* @param element the element to add.
162			* @return <tt>true</tt>
163			* @throws ClassCastException if the specified element cannot be compared
164			* with elements currently in the priority queue according
165			* to the priority queue's ordering.
166			* @throws NullPointerException if the specified element is null.
167	tim	1.2	*/
168	dholmes	1.11	public boolean offer(E element) {
169			if (element == null)
170			throw new NullPointerException();
171			modCount++;
172			++size;
173
174			// Grow backing store if necessary
175			while (size >= queue.length) {
176	tim	1.16	Object[] newQueue = new Object[2 * queue.length];
177	dholmes	1.11	System.arraycopy(queue, 0, newQueue, 0, queue.length);
178			queue = newQueue;
179			}
180
181			queue[size] = element;
182			fixUp(size);
183			return true;
184			}
185
186	tim	1.1	public E poll() {
187	tim	1.2	if (size == 0)
188			return null;
189	tim	1.16	return (E) remove(1);
190	tim	1.1	}
191	tim	1.2
192	tim	1.1	public E peek() {
193	tim	1.16	return (E) queue[1];
194	tim	1.1	}
195
196	tim	1.2	// Collection Methods
197
198	dholmes	1.11	// these first two override just to get the throws docs
199
200			/**
201			* @throws NullPointerException if the specified element is <tt>null</tt>.
202	dholmes	1.15	* @throws ClassCastException if the specified element cannot be compared
203			* with elements currently in the priority queue according
204			* to the priority queue's ordering.
205	dholmes	1.11	*/
206			public boolean add(E element) {
207			return super.add(element);
208			}
209
210	tim	1.14	/**
211			* @throws NullPointerException if any element is <tt>null</tt>.
212	dholmes	1.15	* @throws ClassCastException if any element cannot be compared
213			* with elements currently in the priority queue according
214			* to the priority queue's ordering.
215	tim	1.14	*/
216			public boolean addAll(Collection<? extends E> c) {
217			return super.addAll(c);
218			}
219	dholmes	1.11
220	dl	1.12	public boolean remove(Object o) {
221	dholmes	1.11	if (o == null)
222	dholmes	1.15	return false;
223	tim	1.2
224			if (comparator == null) {
225			for (int i = 1; i <= size; i++) {
226	tim	1.16	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
227	tim	1.2	remove(i);
228			return true;
229			}
230			}
231			} else {
232			for (int i = 1; i <= size; i++) {
233	tim	1.16	if (comparator.compare((E)queue[i], (E)o) == 0) {
234	tim	1.2	remove(i);
235			return true;
236			}
237			}
238			}
239	tim	1.1	return false;
240			}
241	tim	1.2
242			public Iterator<E> iterator() {
243	dl	1.7	return new Itr();
244	tim	1.2	}
245
246			private class Itr implements Iterator<E> {
247	dl	1.7	/**
248			* Index (into queue array) of element to be returned by
249	tim	1.2	* subsequent call to next.
250	dl	1.7	*/
251			private int cursor = 1;
252	tim	1.2
253	dl	1.7	/**
254			* Index of element returned by most recent call to next or
255			* previous. Reset to 0 if this element is deleted by a call
256			* to remove.
257			*/
258			private int lastRet = 0;
259
260			/**
261			* The modCount value that the iterator believes that the backing
262			* List should have. If this expectation is violated, the iterator
263			* has detected concurrent modification.
264			*/
265			private int expectedModCount = modCount;
266	tim	1.2
267	dl	1.7	public boolean hasNext() {
268			return cursor <= size;
269			}
270
271			public E next() {
272	tim	1.2	checkForComodification();
273			if (cursor > size)
274	dl	1.7	throw new NoSuchElementException();
275	tim	1.16	E result = (E) queue[cursor];
276	tim	1.2	lastRet = cursor++;
277			return result;
278	dl	1.7	}
279	tim	1.2
280	dl	1.7	public void remove() {
281			if (lastRet == 0)
282			throw new IllegalStateException();
283	tim	1.2	checkForComodification();
284
285			PriorityQueue.this.remove(lastRet);
286			if (lastRet < cursor)
287			cursor--;
288			lastRet = 0;
289			expectedModCount = modCount;
290	dl	1.7	}
291	tim	1.2
292	dl	1.7	final void checkForComodification() {
293			if (modCount != expectedModCount)
294			throw new ConcurrentModificationException();
295			}
296	tim	1.2	}
297
298			/**
299			* Returns the number of elements in this priority queue.
300	tim	1.10	*
301	tim	1.2	* @return the number of elements in this priority queue.
302			*/
303	tim	1.1	public int size() {
304	tim	1.2	return size;
305	tim	1.1	}
306	tim	1.2
307			/**
308			* Remove all elements from the priority queue.
309			*/
310			public void clear() {
311			modCount++;
312
313			// Null out element references to prevent memory leak
314			for (int i=1; i<=size; i++)
315			queue[i] = null;
316
317			size = 0;
318			}
319
320			/**
321			* Removes and returns the ith element from queue. Recall
322			* that queue is one-based, so 1 <= i <= size.
323			*
324			* XXX: Could further special-case i==size, but is it worth it?
325			* XXX: Could special-case i==0, but is it worth it?
326			*/
327			private E remove(int i) {
328			assert i <= size;
329			modCount++;
330
331	tim	1.16	E result = (E) queue[i];
332	tim	1.2	queue[i] = queue[size];
333			queue[size--] = null; // Drop extra ref to prevent memory leak
334			if (i <= size)
335			fixDown(i);
336			return result;
337	tim	1.1	}
338
339	tim	1.2	/**
340			* Establishes the heap invariant (described above) assuming the heap
341			* satisfies the invariant except possibly for the leaf-node indexed by k
342			* (which may have a nextExecutionTime less than its parent's).
343			*
344			* This method functions by "promoting" queue[k] up the hierarchy
345			* (by swapping it with its parent) repeatedly until queue[k]
346			* is greater than or equal to its parent.
347			*/
348			private void fixUp(int k) {
349			if (comparator == null) {
350			while (k > 1) {
351			int j = k >> 1;
352	tim	1.16	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
353	tim	1.2	break;
354	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
355	tim	1.2	k = j;
356			}
357			} else {
358			while (k > 1) {
359			int j = k >> 1;
360	tim	1.16	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
361	tim	1.2	break;
362	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
363	tim	1.2	k = j;
364			}
365			}
366			}
367
368			/**
369			* Establishes the heap invariant (described above) in the subtree
370			* rooted at k, which is assumed to satisfy the heap invariant except
371			* possibly for node k itself (which may be greater than its children).
372			*
373			* This method functions by "demoting" queue[k] down the hierarchy
374			* (by swapping it with its smaller child) repeatedly until queue[k]
375			* is less than or equal to its children.
376			*/
377			private void fixDown(int k) {
378			int j;
379			if (comparator == null) {
380			while ((j = k << 1) <= size) {
381	tim	1.16	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
382	tim	1.2	j++; // j indexes smallest kid
383	tim	1.16	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
384	tim	1.2	break;
385	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
386	tim	1.2	k = j;
387			}
388			} else {
389			while ((j = k << 1) <= size) {
390	tim	1.16	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
391	tim	1.2	j++; // j indexes smallest kid
392	tim	1.16	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
393	tim	1.2	break;
394	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
395	tim	1.2	k = j;
396			}
397			}
398			}
399
400	tim	1.16	public Comparator<? super E> comparator() {
401	tim	1.2	return comparator;
402			}
403	dl	1.5
404			/**
405			* Save the state of the instance to a stream (that
406			* is, serialize it).
407			*
408			* @serialData The length of the array backing the instance is
409			* emitted (int), followed by all of its elements (each an
410			* <tt>Object</tt>) in the proper order.
411	dl	1.7	* @param s the stream
412	dl	1.5	*/
413			private synchronized void writeObject(java.io.ObjectOutputStream s)
414			throws java.io.IOException{
415	dl	1.7	// Write out element count, and any hidden stuff
416			s.defaultWriteObject();
417	dl	1.5
418			// Write out array length
419			s.writeInt(queue.length);
420
421	dl	1.7	// Write out all elements in the proper order.
422			for (int i=0; i<size; i++)
423	dl	1.5	s.writeObject(queue[i]);
424			}
425
426			/**
427			* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
428			* deserialize it).
429	dl	1.7	* @param s the stream
430	dl	1.5	*/
431			private synchronized void readObject(java.io.ObjectInputStream s)
432			throws java.io.IOException, ClassNotFoundException {
433	dl	1.7	// Read in size, and any hidden stuff
434			s.defaultReadObject();
435	dl	1.5
436			// Read in array length and allocate array
437			int arrayLength = s.readInt();
438	tim	1.16	queue = new Object[arrayLength];
439	dl	1.5
440	dl	1.7	// Read in all elements in the proper order.
441			for (int i=0; i<size; i++)
442	tim	1.16	queue[i] = s.readObject();
443	dl	1.5	}
444
445	tim	1.1	}
446	dholmes	1.11