java/util/PriorityQueue.java

 package java.util;

/*
 * Todo
 *
 *   1) Make it serializable.
 */

/**
 * An unbounded priority queue based on a priority heap.  This queue orders
 * elements according to the order specified at creation time.  This order is
 * specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
 * either according to their <i>natural order</i> (see {@link Comparable}), or
 * according to a {@link Comparator}, depending on which constructor is used.
 * The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
 * minimal element with respect to the specified ordering.  If multiple
 * these elements are tied for least value, no guarantees are made as to
 * which of elements is returned.
 *
 * <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
 * the array used 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 list,
 * 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 <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</tt> methods; and constant time for the <tt>peek</tt>,
 * <tt>element</tt>, and <tt>size</tt> methods.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 */
public class PriorityQueue<E> extends AbstractQueue<E>
                              implements Queue<E>
{
    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
     * of n, d, 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 E[] 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<E> comparator;

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

    /**
     * Create a new priority queue with the default initial capacity (11)
     * that orders its elements according to their natural ordering.
     */
    public PriorityQueue() {
        this(DEFAULT_INITIAL_CAPACITY);
    }

    /**
     * Create a new priority queue with the specified initial capacity
     * that orders its elements according to their natural ordering.
     *
     * @param initialCapacity the initial capacity for this priority queue.
     */
    public PriorityQueue(int initialCapacity) {
        this(initialCapacity, null);
    }

    /**
     * Create a new priority queue with the specified initial capacity (11)
     * 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.
     */
    public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
        if (initialCapacity < 1)
            initialCapacity = 1;
        queue = new E[initialCapacity + 1];
        this.comparator = comparator;
    }

    /**
     * Create a new priority queue containing the elements in the specified
     * collection.  The priority queue has an initial capacity of 110% of the
     * size of the specified collection. 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 the
     * <tt>Sorted</tt> interface, the priority queue is ordered according to
     * its elements' natural order.
     *
     * @param initialElements 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 the specified collection or an
     *         element of the specified collection is <tt>null</tt>.
     */
    public PriorityQueue(Collection<E> initialElements) {
        int sz = initialElements.size();
        int initialCapacity = (int)Math.min((sz * 110L) / 100,
                                            Integer.MAX_VALUE - 1);
        if (initialCapacity < 1)
            initialCapacity = 1;
        queue = new E[initialCapacity + 1];

        /* Commented out to compile with generics compiler

        if (initialElements instanceof Sorted) {
            comparator = ((Sorted)initialElements).comparator();
            for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
                queue[++size] = i.next();
        } else {
        */
        {
            comparator = null;
            for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
                add(i.next());
        }
    }

    // Queue Methods

    /**
     * Remove and return the minimal element from this priority queue if
     * it contains one or more elements, otherwise <tt>null</tt>.  The term
     * <i>minimal</i> is defined according to this priority queue's order.
     *
     * @return the minimal element from this priority queue if it contains
     *         one or more elements, otherwise <tt>null</tt>.
     */
    public E poll() {
        if (size == 0)
            return null;
        return remove(1);
    }

    /**
     * Return, but do not remove, the minimal element from the priority queue,
     * or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
     * defined according to this priority queue's order.  This method returns
     * the same object reference that would be returned by by the
     * <tt>poll</tt> method.  The two methods differ in that this method
     * does not remove the element from the priority queue.
     *
     * @return the minimal element from this priority queue if it contains
     *         one or more elements, otherwise <tt>null</tt>.
     */
    public E peek() {
        return queue[1];
    }

    // Collection Methods

    /**
     * Removes a single instance of the specified element from this priority
     * queue, if it is present.  Returns true if this collection contained the
     * specified element (or equivalently, if this collection changed as a
     * result of the call).
     *
     * @param o element to be removed from this collection, if present.
     * @return <tt>true</tt> if this collection changed as a result of the
     *         call
     * @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 remove(Object element) {
        if (element == null)
            throw new NullPointerException();

        if (comparator == null) {
            for (int i = 1; i <= size; i++) {
                if (((Comparable)queue[i]).compareTo(element) == 0) {
                    remove(i);
                    return true;
                }
            }
        } else {
            for (int i = 1; i <= size; i++) {
                if (comparator.compare(queue[i], (E) element) == 0) {
                    remove(i);
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * Returns an iterator over the elements in this priority queue.  The
     * first element returned by this iterator is the same element that
     * would be returned by a call to <tt>peek</tt>.
     *
     * @return an <tt>Iterator</tt> over the elements in this priority 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.
         */
        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.
         */
        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.
         */
        int expectedModCount = modCount;

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

        public E next() {
            checkForComodification();
            if (cursor > size)
                throw new NoSuchElementException();
            E result = 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;
    }

    /**
     * Add the specified element to this priority queue.
     *
     * @param element the element to add.
     * @return true
     * @throws ClassCastException if the specified element cannot be compared
     *            with elements currently in the priority queue according
     *            to the priority queue's ordering.
     * @throws NullPointerException if the specified element is null.
     */
    public boolean offer(E element) {
        if (element == null)
            throw new NullPointerException();
        modCount++;

        // Grow backing store if necessary
        if (++size == queue.length) {
            E[] newQueue = new E[2 * queue.length];
            System.arraycopy(queue, 0, newQueue, 0, size);
            queue = newQueue;
        }

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

    /**
     * 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 = 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)queue[j]).compareTo(queue[k]) <= 0)
                    break;
                E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
                k = j;
            }
        } else {
            while (k > 1) {
                int j = k >> 1;
                if (comparator.compare(queue[j], queue[k]) <= 0)
                    break;
                E 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)queue[j]).compareTo(queue[j+1]) > 0)
                    j++; // j indexes smallest kid
                if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
                    break;
                E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
                k = j;
            }
        } else {
            while ((j = k << 1) <= size) {
                if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
                    j++; // j indexes smallest kid
                if (comparator.compare(queue[k], queue[j]) <= 0)
                    break;
                E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
                k = j;
            }
        }
    }

    /**
     * Returns the comparator associated with this priority queue, or
     * <tt>null</tt> if it uses its elements' natural ordering.
     *
     * @return the comparator associated with this priority queue, or
     *         <tt>null</tt> if it uses its elements' natural ordering.
     */
    Comparator<E> comparator() {
        return comparator;
    }
}
Revision:	1.3
Committed:	Sun May 18 20:36:01 2003 UTC (20 years, 11 months ago) by tim
Branch:	MAIN
Changes since 1.2:	+1 -1 lines
Log Message:	Added another type parameter
#	Content
1	package java.util;
2
3	/*
4	* Todo
5	*
6	* 1) Make it serializable.
7	*/
8
9	/**
10	* An unbounded priority queue based on a priority heap. This queue orders
11	* elements according to the order specified at creation time. This order is
12	* specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
13	* either according to their <i>natural order</i> (see {@link Comparable}), or
14	* according to a {@link Comparator}, depending on which constructor is used.
15	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
16	* minimal element with respect to the specified ordering. If multiple
17	* these elements are tied for least value, no guarantees are made as to
18	* which of elements is returned.
19	*
20	* <p>Each priority queue has a <i>capacity</i>. The capacity is the size of
21	* the array used to store the elements on the queue. It is always at least
22	* as large as the queue size. As elements are added to a priority list,
23	* its capacity grows automatically. The details of the growth policy are not
24	* specified.
25	*
26	*<p>Implementation note: this implementation provides O(log(n)) time for
27	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
28	* methods; linear time for the <tt>remove(Object)</tt> and
29	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
30	* <tt>element</tt>, and <tt>size</tt> methods.
31	*
32	* <p>This class is a member of the
33	* <a href="{@docRoot}/../guide/collections/index.html">
34	* Java Collections Framework</a>.
35	*/
36	public class PriorityQueue<E> extends AbstractQueue<E>
37	implements Queue<E>
38	{
39	private static final int DEFAULT_INITIAL_CAPACITY = 11;
40
41	/**
42	* Priority queue represented as a balanced binary heap: the two children
43	* of queue[n] are queue[2n] and queue[2n + 1]. The priority queue is
44	* ordered by comparator, or by the elements' natural ordering, if
45	* comparator is null: For each node n in the heap, and each descendant
46	* of n, d, n <= d.
47	*
48	* The element with the lowest value is in queue[1] (assuming the queue is
49	* nonempty). A one-based array is used in preference to the traditional
50	* zero-based array to simplify parent and child calculations.
51	*
52	* queue.length must be >= 2, even if size == 0.
53	*/
54	private E[] queue;
55
56	/**
57	* The number of elements in the priority queue.
58	*/
59	private int size = 0;
60
61	/**
62	* The comparator, or null if priority queue uses elements'
63	* natural ordering.
64	*/
65	private final Comparator<E> comparator;
66
67	/**
68	* The number of times this priority queue has been
69	* <i>structurally modified</i>. See AbstractList for gory details.
70	*/
71	private int modCount = 0;
72
73	/**
74	* Create a new priority queue with the default initial capacity (11)
75	* that orders its elements according to their natural ordering.
76	*/
77	public PriorityQueue() {
78	this(DEFAULT_INITIAL_CAPACITY);
79	}
80
81	/**
82	* Create a new priority queue with the specified initial capacity
83	* that orders its elements according to their natural ordering.
84	*
85	* @param initialCapacity the initial capacity for this priority queue.
86	*/
87	public PriorityQueue(int initialCapacity) {
88	this(initialCapacity, null);
89	}
90
91	/**
92	* Create a new priority queue with the specified initial capacity (11)
93	* that orders its elements according to the specified comparator.
94	*
95	* @param initialCapacity the initial capacity for this priority queue.
96	* @param comparator the comparator used to order this priority queue.
97	*/
98	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
99	if (initialCapacity < 1)
100	initialCapacity = 1;
101	queue = new E[initialCapacity + 1];
102	this.comparator = comparator;
103	}
104
105	/**
106	* Create a new priority queue containing the elements in the specified
107	* collection. The priority queue has an initial capacity of 110% of the
108	* size of the specified collection. If the specified collection
109	* implements the {@link Sorted} interface, the priority queue will be
110	* sorted according to the same comparator, or according to its elements'
111	* natural order if the collection is sorted according to its elements'
112	* natural order. If the specified collection does not implement the
113	* <tt>Sorted</tt> interface, the priority queue is ordered according to
114	* its elements' natural order.
115	*
116	* @param initialElements the collection whose elements are to be placed
117	* into this priority queue.
118	* @throws ClassCastException if elements of the specified collection
119	* cannot be compared to one another according to the priority
120	* queue's ordering.
121	* @throws NullPointerException if the specified collection or an
122	* element of the specified collection is <tt>null</tt>.
123	*/
124	public PriorityQueue(Collection<E> initialElements) {
125	int sz = initialElements.size();
126	int initialCapacity = (int)Math.min((sz * 110L) / 100,
127	Integer.MAX_VALUE - 1);
128	if (initialCapacity < 1)
129	initialCapacity = 1;
130	queue = new E[initialCapacity + 1];
131
132	/* Commented out to compile with generics compiler
133
134	if (initialElements instanceof Sorted) {
135	comparator = ((Sorted)initialElements).comparator();
136	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
137	queue[++size] = i.next();
138	} else {
139	*/
140	{
141	comparator = null;
142	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	add(i.next());
144	}
145	}
146
147	// Queue Methods
148
149	/**
150	* Remove and return the minimal element from this priority queue if
151	* it contains one or more elements, otherwise <tt>null</tt>. The term
152	* <i>minimal</i> is defined according to this priority queue's order.
153	*
154	* @return the minimal element from this priority queue if it contains
155	* one or more elements, otherwise <tt>null</tt>.
156	*/
157	public E poll() {
158	if (size == 0)
159	return null;
160	return remove(1);
161	}
162
163	/**
164	* Return, but do not remove, the minimal element from the priority queue,
165	* or <tt>null</tt> if the queue is empty. The term <i>minimal</i> is
166	* defined according to this priority queue's order. This method returns
167	* the same object reference that would be returned by by the
168	* <tt>poll</tt> method. The two methods differ in that this method
169	* does not remove the element from the priority queue.
170	*
171	* @return the minimal element from this priority queue if it contains
172	* one or more elements, otherwise <tt>null</tt>.
173	*/
174	public E peek() {
175	return queue[1];
176	}
177
178	// Collection Methods
179
180	/**
181	* Removes a single instance of the specified element from this priority
182	* queue, if it is present. Returns true if this collection contained the
183	* specified element (or equivalently, if this collection changed as a
184	* result of the call).
185	*
186	* @param o element to be removed from this collection, if present.
187	* @return <tt>true</tt> if this collection changed as a result of the
188	* call
189	* @throws ClassCastException if the specified element cannot be compared
190	* with elements currently in the priority queue according
191	* to the priority queue's ordering.
192	* @throws NullPointerException if the specified element is null.
193	*/
194	public boolean remove(Object element) {
195	if (element == null)
196	throw new NullPointerException();
197
198	if (comparator == null) {
199	for (int i = 1; i <= size; i++) {
200	if (((Comparable)queue[i]).compareTo(element) == 0) {
201	remove(i);
202	return true;
203	}
204	}
205	} else {
206	for (int i = 1; i <= size; i++) {
207	if (comparator.compare(queue[i], (E) element) == 0) {
208	remove(i);
209	return true;
210	}
211	}
212	}
213	return false;
214	}
215
216	/**
217	* Returns an iterator over the elements in this priority queue. The
218	* first element returned by this iterator is the same element that
219	* would be returned by a call to <tt>peek</tt>.
220	*
221	* @return an <tt>Iterator</tt> over the elements in this priority queue.
222	*/
223	public Iterator<E> iterator() {
224	return new Itr();
225	}
226
227	private class Itr implements Iterator<E> {
228	/**
229	* Index (into queue array) of element to be returned by
230	* subsequent call to next.
231	*/
232	int cursor = 1;
233
234	/**
235	* Index of element returned by most recent call to next or
236	* previous. Reset to 0 if this element is deleted by a call
237	* to remove.
238	*/
239	int lastRet = 0;
240
241	/**
242	* The modCount value that the iterator believes that the backing
243	* List should have. If this expectation is violated, the iterator
244	* has detected concurrent modification.
245	*/
246	int expectedModCount = modCount;
247
248	public boolean hasNext() {
249	return cursor <= size;
250	}
251
252	public E next() {
253	checkForComodification();
254	if (cursor > size)
255	throw new NoSuchElementException();
256	E result = queue[cursor];
257	lastRet = cursor++;
258	return result;
259	}
260
261	public void remove() {
262	if (lastRet == 0)
263	throw new IllegalStateException();
264	checkForComodification();
265
266	PriorityQueue.this.remove(lastRet);
267	if (lastRet < cursor)
268	cursor--;
269	lastRet = 0;
270	expectedModCount = modCount;
271	}
272
273	final void checkForComodification() {
274	if (modCount != expectedModCount)
275	throw new ConcurrentModificationException();
276	}
277	}
278
279	/**
280	* Returns the number of elements in this priority queue.
281	*
282	* @return the number of elements in this priority queue.
283	*/
284	public int size() {
285	return size;
286	}
287
288	/**
289	* Add the specified element to this priority queue.
290	*
291	* @param element the element to add.
292	* @return true
293	* @throws ClassCastException if the specified element cannot be compared
294	* with elements currently in the priority queue according
295	* to the priority queue's ordering.
296	* @throws NullPointerException if the specified element is null.
297	*/
298	public boolean offer(E element) {
299	if (element == null)
300	throw new NullPointerException();
301	modCount++;
302
303	// Grow backing store if necessary
304	if (++size == queue.length) {
305	E[] newQueue = new E[2 * queue.length];
306	System.arraycopy(queue, 0, newQueue, 0, size);
307	queue = newQueue;
308	}
309
310	queue[size] = element;
311	fixUp(size);
312	return true;
313	}
314
315	/**
316	* Remove all elements from the priority queue.
317	*/
318	public void clear() {
319	modCount++;
320
321	// Null out element references to prevent memory leak
322	for (int i=1; i<=size; i++)
323	queue[i] = null;
324
325	size = 0;
326	}
327
328	/**
329	* Removes and returns the ith element from queue. Recall
330	* that queue is one-based, so 1 <= i <= size.
331	*
332	* XXX: Could further special-case i==size, but is it worth it?
333	* XXX: Could special-case i==0, but is it worth it?
334	*/
335	private E remove(int i) {
336	assert i <= size;
337	modCount++;
338
339	E result = queue[i];
340	queue[i] = queue[size];
341	queue[size--] = null; // Drop extra ref to prevent memory leak
342	if (i <= size)
343	fixDown(i);
344	return result;
345	}
346
347	/**
348	* Establishes the heap invariant (described above) assuming the heap
349	* satisfies the invariant except possibly for the leaf-node indexed by k
350	* (which may have a nextExecutionTime less than its parent's).
351	*
352	* This method functions by "promoting" queue[k] up the hierarchy
353	* (by swapping it with its parent) repeatedly until queue[k]
354	* is greater than or equal to its parent.
355	*/
356	private void fixUp(int k) {
357	if (comparator == null) {
358	while (k > 1) {
359	int j = k >> 1;
360	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
361	break;
362	E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
363	k = j;
364	}
365	} else {
366	while (k > 1) {
367	int j = k >> 1;
368	if (comparator.compare(queue[j], queue[k]) <= 0)
369	break;
370	E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
371	k = j;
372	}
373	}
374	}
375
376	/**
377	* Establishes the heap invariant (described above) in the subtree
378	* rooted at k, which is assumed to satisfy the heap invariant except
379	* possibly for node k itself (which may be greater than its children).
380	*
381	* This method functions by "demoting" queue[k] down the hierarchy
382	* (by swapping it with its smaller child) repeatedly until queue[k]
383	* is less than or equal to its children.
384	*/
385	private void fixDown(int k) {
386	int j;
387	if (comparator == null) {
388	while ((j = k << 1) <= size) {
389	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
390	j++; // j indexes smallest kid
391	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
392	break;
393	E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
394	k = j;
395	}
396	} else {
397	while ((j = k << 1) <= size) {
398	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
399	j++; // j indexes smallest kid
400	if (comparator.compare(queue[k], queue[j]) <= 0)
401	break;
402	E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
403	k = j;
404	}
405	}
406	}
407
408	/**
409	* Returns the comparator associated with this priority queue, or
410	* <tt>null</tt> if it uses its elements' natural ordering.
411	*
412	* @return the comparator associated with this priority queue, or
413	* <tt>null</tt> if it uses its elements' natural ordering.
414	*/
415	Comparator<E> comparator() {
416	return comparator;
417	}
418	}