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.
 * <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 Sorted, 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) {
            comparator = (Comparator<? super E>)((Sorted)c).comparator();
        } 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.
     *
     * @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
        while (size >= queue.length) {
            Object[] newQueue = new Object[2 * queue.length];
            System.arraycopy(queue, 0, newQueue, 0, queue.length);
            queue = newQueue;
        }

        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

    // 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 o) {
        return super.add(o);
    }

    /**
     * @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);
    }

    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:	1.20
Committed:	Tue Aug 5 06:18:17 2003 UTC (20 years, 9 months ago) by dholmes
Branch:	MAIN
Changes since 1.19:	+3 -9 lines
Log Message:	Regressed to describing a PQ as unbounded.
#	User	Rev	Content
1	tim	1.2	package java.util;
2	tim	1.1
3			/**
4	dholmes	1.20	* 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	1.19	* specified in the same manner as {@link java.util.TreeSet} and
7	dholmes	1.18	* {@link java.util.TreeMap}: elements are ordered
8	tim	1.2	* either according to their <i>natural order</i> (see {@link Comparable}), or
9	tim	1.19	* according to a {@link java.util.Comparator}, depending on which
10	dholmes	1.18	* constructor is used.
11	tim	1.19	* <p>The <em>head</em> of this queue is the <em>least</em> element with
12			* respect to the specified ordering.
13	dholmes	1.18	* If multiple elements are tied for least value, the
14	tim	1.14	* head is one of those elements. A priority queue does not permit
15	dholmes	1.11	* <tt>null</tt> elements.
16	tim	1.14	*
17	dholmes	1.11	* <p>The {@link #remove()} and {@link #poll()} methods remove and
18			* return the head of the queue.
19			*
20			* <p>The {@link #element()} and {@link #peek()} methods return, but do
21			* not delete, the head of the queue.
22	tim	1.2	*
23	dl	1.7	* <p>A priority queue has a <i>capacity</i>. The capacity is the
24			* size of the array used internally to store the elements on the
25	dholmes	1.20	* queue.
26	dholmes	1.18	* It is always at least as large as the queue size. As
27	dl	1.7	* elements are added to a priority queue, its capacity grows
28			* automatically. The details of the growth policy are not specified.
29	tim	1.2	*
30	dholmes	1.11	* <p>Implementation note: this implementation provides O(log(n)) time
31			* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
32			* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
33			* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
34			* constant time for the retrieval methods (<tt>peek</tt>,
35			* <tt>element</tt>, and <tt>size</tt>).
36	tim	1.2	*
37			* <p>This class is a member of the
38			* <a href="{@docRoot}/../guide/collections/index.html">
39			* Java Collections Framework</a>.
40	dl	1.7	* @since 1.5
41			* @author Josh Bloch
42	tim	1.2	*/
43			public class PriorityQueue<E> extends AbstractQueue<E>
44	dholmes	1.18	implements Sorted, Queue<E>, java.io.Serializable {
45	dholmes	1.11
46	tim	1.2	private static final int DEFAULT_INITIAL_CAPACITY = 11;
47	tim	1.1
48	tim	1.2	/**
49			* Priority queue represented as a balanced binary heap: the two children
50			* of queue[n] are queue[2n] and queue[2n + 1]. The priority queue is
51			* ordered by comparator, or by the elements' natural ordering, if
52	brian	1.6	* comparator is null: For each node n in the heap and each descendant d
53			* of n, n <= d.
54	tim	1.2	*
55	brian	1.6	* The element with the lowest value is in queue[1], assuming the queue is
56			* nonempty. (A one-based array is used in preference to the traditional
57			* zero-based array to simplify parent and child calculations.)
58	tim	1.2	*
59			* queue.length must be >= 2, even if size == 0.
60			*/
61	tim	1.16	private transient Object[] queue;
62	tim	1.1
63	tim	1.2	/**
64			* The number of elements in the priority queue.
65			*/
66			private int size = 0;
67	tim	1.1
68	tim	1.2	/**
69			* The comparator, or null if priority queue uses elements'
70			* natural ordering.
71			*/
72	tim	1.16	private final Comparator<? super E> comparator;
73	tim	1.2
74			/**
75			* The number of times this priority queue has been
76			* <i>structurally modified</i>. See AbstractList for gory details.
77			*/
78	dl	1.5	private transient int modCount = 0;
79	tim	1.2
80			/**
81	dholmes	1.11	* Create a <tt>PriorityQueue</tt> with the default initial capacity
82	dl	1.7	* (11) that orders its elements according to their natural
83			* ordering (using <tt>Comparable</tt>.)
84	tim	1.2	*/
85			public PriorityQueue() {
86	dholmes	1.11	this(DEFAULT_INITIAL_CAPACITY, null);
87	tim	1.1	}
88	tim	1.2
89			/**
90	dholmes	1.11	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
91	dl	1.7	* that orders its elements according to their natural ordering
92			* (using <tt>Comparable</tt>.)
93	tim	1.2	*
94			* @param initialCapacity the initial capacity for this priority queue.
95			*/
96			public PriorityQueue(int initialCapacity) {
97			this(initialCapacity, null);
98	tim	1.1	}
99	tim	1.2
100			/**
101	dholmes	1.11	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
102	tim	1.2	* that orders its elements according to the specified comparator.
103			*
104			* @param initialCapacity the initial capacity for this priority queue.
105			* @param comparator the comparator used to order this priority queue.
106	dholmes	1.11	* If <tt>null</tt> then the order depends on the elements' natural
107			* ordering.
108	dholmes	1.15	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
109			* than 1
110	tim	1.2	*/
111	tim	1.16	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
112	tim	1.2	if (initialCapacity < 1)
113	dholmes	1.15	throw new IllegalArgumentException();
114	tim	1.16	this.queue = new Object[initialCapacity + 1];
115	tim	1.2	this.comparator = comparator;
116	tim	1.1	}
117
118	tim	1.2	/**
119	dholmes	1.11	* Create a <tt>PriorityQueue</tt> containing the elements in the specified
120	tim	1.2	* collection. The priority queue has an initial capacity of 110% of the
121	dholmes	1.20	* size of the specified collection or 1 if the collection is empty.
122	dholmes	1.15	* If the specified collection
123	tim	1.2	* implements the {@link Sorted} interface, the priority queue will be
124			* sorted according to the same comparator, or according to its elements'
125			* natural order if the collection is sorted according to its elements'
126	brian	1.6	* natural order. If the specified collection does not implement
127			* <tt>Sorted</tt>, the priority queue is ordered according to
128	tim	1.2	* its elements' natural order.
129			*
130	dholmes	1.15	* @param c the collection whose elements are to be placed
131	tim	1.2	* into this priority queue.
132			* @throws ClassCastException if elements of the specified collection
133			* cannot be compared to one another according to the priority
134			* queue's ordering.
135	dholmes	1.15	* @throws NullPointerException if <tt>c</tt> or any element within it
136			* is <tt>null</tt>
137	tim	1.2	*/
138	tim	1.16	public PriorityQueue(Collection<? extends E> c) {
139	dholmes	1.15	int sz = c.size();
140	tim	1.2	int initialCapacity = (int)Math.min((sz * 110L) / 100,
141			Integer.MAX_VALUE - 1);
142			if (initialCapacity < 1)
143			initialCapacity = 1;
144	dholmes	1.15
145	tim	1.16	this.queue = new Object[initialCapacity + 1];
146	tim	1.2
147	dholmes	1.15	if (c instanceof Sorted) {
148	tim	1.19	comparator = (Comparator<? super E>)((Sorted)c).comparator();
149	tim	1.2	} else {
150			comparator = null;
151			}
152	dholmes	1.18
153			for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
154			add(i.next());
155	tim	1.1	}
156
157	tim	1.2	// Queue Methods
158
159			/**
160	dholmes	1.11	* Add the specified element to this priority queue.
161	tim	1.2	*
162	dholmes	1.11	* @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	dholmes	1.18	* @throws NullPointerException if the specified element is <tt>null</tt>.
167	tim	1.2	*/
168	dholmes	1.18	public boolean offer(E o) {
169			if (o == null)
170	dholmes	1.11	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	dholmes	1.18	queue[size] = o;
182	dholmes	1.11	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	dholmes	1.18	public boolean add(E o) {
207			return super.add(o);
208	dholmes	1.11	}
209
210	tim	1.14	/**
211	dholmes	1.15	* @throws ClassCastException if any element cannot be compared
212			* with elements currently in the priority queue according
213			* to the priority queue's ordering.
214	dholmes	1.18	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
215			* is <tt>null</tt>
216	tim	1.14	*/
217			public boolean addAll(Collection<? extends E> c) {
218			return super.addAll(c);
219			}
220	dholmes	1.11
221	dl	1.12	public boolean remove(Object o) {
222	dholmes	1.11	if (o == null)
223	dholmes	1.15	return false;
224	tim	1.2
225			if (comparator == null) {
226			for (int i = 1; i <= size; i++) {
227	tim	1.16	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
228	tim	1.2	remove(i);
229			return true;
230			}
231			}
232			} else {
233			for (int i = 1; i <= size; i++) {
234	tim	1.16	if (comparator.compare((E)queue[i], (E)o) == 0) {
235	tim	1.2	remove(i);
236			return true;
237			}
238			}
239			}
240	tim	1.1	return false;
241			}
242	tim	1.2
243			public Iterator<E> iterator() {
244	dl	1.7	return new Itr();
245	tim	1.2	}
246
247			private class Itr implements Iterator<E> {
248	dl	1.7	/**
249			* Index (into queue array) of element to be returned by
250	tim	1.2	* subsequent call to next.
251	dl	1.7	*/
252			private int cursor = 1;
253	tim	1.2
254	dl	1.7	/**
255			* Index of element returned by most recent call to next or
256			* previous. Reset to 0 if this element is deleted by a call
257			* to remove.
258			*/
259			private int lastRet = 0;
260
261			/**
262			* The modCount value that the iterator believes that the backing
263			* List should have. If this expectation is violated, the iterator
264			* has detected concurrent modification.
265			*/
266			private int expectedModCount = modCount;
267	tim	1.2
268	dl	1.7	public boolean hasNext() {
269			return cursor <= size;
270			}
271
272			public E next() {
273	tim	1.2	checkForComodification();
274			if (cursor > size)
275	dl	1.7	throw new NoSuchElementException();
276	tim	1.16	E result = (E) queue[cursor];
277	tim	1.2	lastRet = cursor++;
278			return result;
279	dl	1.7	}
280	tim	1.2
281	dl	1.7	public void remove() {
282			if (lastRet == 0)
283			throw new IllegalStateException();
284	tim	1.2	checkForComodification();
285
286			PriorityQueue.this.remove(lastRet);
287			if (lastRet < cursor)
288			cursor--;
289			lastRet = 0;
290			expectedModCount = modCount;
291	dl	1.7	}
292	tim	1.2
293	dl	1.7	final void checkForComodification() {
294			if (modCount != expectedModCount)
295			throw new ConcurrentModificationException();
296			}
297	tim	1.2	}
298
299			/**
300			* Returns the number of elements in this priority queue.
301	tim	1.10	*
302	tim	1.2	* @return the number of elements in this priority queue.
303			*/
304	tim	1.1	public int size() {
305	tim	1.2	return size;
306	tim	1.1	}
307	tim	1.2
308			/**
309			* Remove all elements from the priority queue.
310			*/
311			public void clear() {
312			modCount++;
313
314			// Null out element references to prevent memory leak
315			for (int i=1; i<=size; i++)
316			queue[i] = null;
317
318			size = 0;
319			}
320
321			/**
322			* Removes and returns the ith element from queue. Recall
323			* that queue is one-based, so 1 <= i <= size.
324			*
325			* XXX: Could further special-case i==size, but is it worth it?
326			* XXX: Could special-case i==0, but is it worth it?
327			*/
328			private E remove(int i) {
329			assert i <= size;
330			modCount++;
331
332	tim	1.16	E result = (E) queue[i];
333	tim	1.2	queue[i] = queue[size];
334			queue[size--] = null; // Drop extra ref to prevent memory leak
335			if (i <= size)
336			fixDown(i);
337			return result;
338	tim	1.1	}
339
340	tim	1.2	/**
341			* Establishes the heap invariant (described above) assuming the heap
342			* satisfies the invariant except possibly for the leaf-node indexed by k
343			* (which may have a nextExecutionTime less than its parent's).
344			*
345			* This method functions by "promoting" queue[k] up the hierarchy
346			* (by swapping it with its parent) repeatedly until queue[k]
347			* is greater than or equal to its parent.
348			*/
349			private void fixUp(int k) {
350			if (comparator == null) {
351			while (k > 1) {
352			int j = k >> 1;
353	tim	1.16	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
354	tim	1.2	break;
355	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
356	tim	1.2	k = j;
357			}
358			} else {
359			while (k > 1) {
360			int j = k >> 1;
361	tim	1.16	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
362	tim	1.2	break;
363	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
364	tim	1.2	k = j;
365			}
366			}
367			}
368
369			/**
370			* Establishes the heap invariant (described above) in the subtree
371			* rooted at k, which is assumed to satisfy the heap invariant except
372			* possibly for node k itself (which may be greater than its children).
373			*
374			* This method functions by "demoting" queue[k] down the hierarchy
375			* (by swapping it with its smaller child) repeatedly until queue[k]
376			* is less than or equal to its children.
377			*/
378			private void fixDown(int k) {
379			int j;
380			if (comparator == null) {
381			while ((j = k << 1) <= size) {
382	tim	1.16	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
383	tim	1.2	j++; // j indexes smallest kid
384	tim	1.16	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
385	tim	1.2	break;
386	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
387	tim	1.2	k = j;
388			}
389			} else {
390			while ((j = k << 1) <= size) {
391	tim	1.16	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
392	tim	1.2	j++; // j indexes smallest kid
393	tim	1.16	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
394	tim	1.2	break;
395	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
396	tim	1.2	k = j;
397			}
398			}
399			}
400
401	tim	1.16	public Comparator<? super E> comparator() {
402	tim	1.2	return comparator;
403			}
404	dl	1.5
405			/**
406			* Save the state of the instance to a stream (that
407			* is, serialize it).
408			*
409			* @serialData The length of the array backing the instance is
410			* emitted (int), followed by all of its elements (each an
411			* <tt>Object</tt>) in the proper order.
412	dl	1.7	* @param s the stream
413	dl	1.5	*/
414			private synchronized void writeObject(java.io.ObjectOutputStream s)
415			throws java.io.IOException{
416	dl	1.7	// Write out element count, and any hidden stuff
417			s.defaultWriteObject();
418	dl	1.5
419			// Write out array length
420			s.writeInt(queue.length);
421
422	dl	1.7	// Write out all elements in the proper order.
423			for (int i=0; i<size; i++)
424	dl	1.5	s.writeObject(queue[i]);
425			}
426
427			/**
428			* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
429			* deserialize it).
430	dl	1.7	* @param s the stream
431	dl	1.5	*/
432			private synchronized void readObject(java.io.ObjectInputStream s)
433			throws java.io.IOException, ClassNotFoundException {
434	dl	1.7	// Read in size, and any hidden stuff
435			s.defaultReadObject();
436	dl	1.5
437			// Read in array length and allocate array
438			int arrayLength = s.readInt();
439	tim	1.16	queue = new Object[arrayLength];
440	dl	1.5
441	dl	1.7	// Read in all elements in the proper order.
442			for (int i=0; i<size; i++)
443	tim	1.16	queue[i] = s.readObject();
444	dl	1.5	}
445
446	tim	1.1	}
447	dholmes	1.11