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;

    /**
     * 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.
     */
    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;
    }

    /**
     * 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
     * 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:	1.21
Committed:	Tue Aug 5 06:49:51 2003 UTC (20 years, 9 months ago) by dholmes
Branch:	MAIN
Changes since 1.20:	+6 -5 lines
Log Message:	MOre tense changes
#	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	1.21	* Creates 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	1.21	* Creates 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	1.21	* Creates 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	1.21	* Creates a <tt>PriorityQueue</tt> containing the elements in the
120			* specified collection.
121			* The priority queue has an initial capacity of 110% of the
122	dholmes	1.20	* size of the specified collection or 1 if the collection is empty.
123	dholmes	1.15	* If the specified collection
124	tim	1.2	* implements the {@link Sorted} interface, the priority queue will be
125			* sorted according to the same comparator, or according to its elements'
126			* natural order if the collection is sorted according to its elements'
127	brian	1.6	* natural order. If the specified collection does not implement
128			* <tt>Sorted</tt>, the priority queue is ordered according to
129	tim	1.2	* its elements' natural order.
130			*
131	dholmes	1.15	* @param c the collection whose elements are to be placed
132	tim	1.2	* into this priority queue.
133			* @throws ClassCastException if elements of the specified collection
134			* cannot be compared to one another according to the priority
135			* queue's ordering.
136	dholmes	1.15	* @throws NullPointerException if <tt>c</tt> or any element within it
137			* is <tt>null</tt>
138	tim	1.2	*/
139	tim	1.16	public PriorityQueue(Collection<? extends E> c) {
140	dholmes	1.15	int sz = c.size();
141	tim	1.2	int initialCapacity = (int)Math.min((sz * 110L) / 100,
142			Integer.MAX_VALUE - 1);
143			if (initialCapacity < 1)
144			initialCapacity = 1;
145	dholmes	1.15
146	tim	1.16	this.queue = new Object[initialCapacity + 1];
147	tim	1.2
148	dholmes	1.15	if (c instanceof Sorted) {
149	tim	1.19	comparator = (Comparator<? super E>)((Sorted)c).comparator();
150	tim	1.2	} else {
151			comparator = null;
152			}
153	dholmes	1.18
154			for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
155			add(i.next());
156	tim	1.1	}
157
158	tim	1.2	// Queue Methods
159
160			/**
161	dholmes	1.11	* Add the specified element to this priority queue.
162	tim	1.2	*
163	dholmes	1.11	* @return <tt>true</tt>
164			* @throws ClassCastException if the specified element cannot be compared
165			* with elements currently in the priority queue according
166			* to the priority queue's ordering.
167	dholmes	1.18	* @throws NullPointerException if the specified element is <tt>null</tt>.
168	tim	1.2	*/
169	dholmes	1.18	public boolean offer(E o) {
170			if (o == null)
171	dholmes	1.11	throw new NullPointerException();
172			modCount++;
173			++size;
174
175			// Grow backing store if necessary
176			while (size >= queue.length) {
177	tim	1.16	Object[] newQueue = new Object[2 * queue.length];
178	dholmes	1.11	System.arraycopy(queue, 0, newQueue, 0, queue.length);
179			queue = newQueue;
180			}
181
182	dholmes	1.18	queue[size] = o;
183	dholmes	1.11	fixUp(size);
184			return true;
185			}
186
187	tim	1.1	public E poll() {
188	tim	1.2	if (size == 0)
189			return null;
190	tim	1.16	return (E) remove(1);
191	tim	1.1	}
192	tim	1.2
193	tim	1.1	public E peek() {
194	tim	1.16	return (E) queue[1];
195	tim	1.1	}
196
197	tim	1.2	// Collection Methods
198
199	dholmes	1.11	// these first two override just to get the throws docs
200
201			/**
202			* @throws NullPointerException if the specified element is <tt>null</tt>.
203	dholmes	1.15	* @throws ClassCastException if the specified element cannot be compared
204			* with elements currently in the priority queue according
205			* to the priority queue's ordering.
206	dholmes	1.11	*/
207	dholmes	1.18	public boolean add(E o) {
208			return super.add(o);
209	dholmes	1.11	}
210
211	tim	1.14	/**
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	dholmes	1.18	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
216			* is <tt>null</tt>
217	tim	1.14	*/
218			public boolean addAll(Collection<? extends E> c) {
219			return super.addAll(c);
220			}
221	dholmes	1.11
222	dl	1.12	public boolean remove(Object o) {
223	dholmes	1.11	if (o == null)
224	dholmes	1.15	return false;
225	tim	1.2
226			if (comparator == null) {
227			for (int i = 1; i <= size; i++) {
228	tim	1.16	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
229	tim	1.2	remove(i);
230			return true;
231			}
232			}
233			} else {
234			for (int i = 1; i <= size; i++) {
235	tim	1.16	if (comparator.compare((E)queue[i], (E)o) == 0) {
236	tim	1.2	remove(i);
237			return true;
238			}
239			}
240			}
241	tim	1.1	return false;
242			}
243	tim	1.2
244			public Iterator<E> iterator() {
245	dl	1.7	return new Itr();
246	tim	1.2	}
247
248			private class Itr implements Iterator<E> {
249	dl	1.7	/**
250			* Index (into queue array) of element to be returned by
251	tim	1.2	* subsequent call to next.
252	dl	1.7	*/
253			private int cursor = 1;
254	tim	1.2
255	dl	1.7	/**
256			* Index of element returned by most recent call to next or
257			* previous. Reset to 0 if this element is deleted by a call
258			* to remove.
259			*/
260			private int lastRet = 0;
261
262			/**
263			* The modCount value that the iterator believes that the backing
264			* List should have. If this expectation is violated, the iterator
265			* has detected concurrent modification.
266			*/
267			private int expectedModCount = modCount;
268	tim	1.2
269	dl	1.7	public boolean hasNext() {
270			return cursor <= size;
271			}
272
273			public E next() {
274	tim	1.2	checkForComodification();
275			if (cursor > size)
276	dl	1.7	throw new NoSuchElementException();
277	tim	1.16	E result = (E) queue[cursor];
278	tim	1.2	lastRet = cursor++;
279			return result;
280	dl	1.7	}
281	tim	1.2
282	dl	1.7	public void remove() {
283			if (lastRet == 0)
284			throw new IllegalStateException();
285	tim	1.2	checkForComodification();
286
287			PriorityQueue.this.remove(lastRet);
288			if (lastRet < cursor)
289			cursor--;
290			lastRet = 0;
291			expectedModCount = modCount;
292	dl	1.7	}
293	tim	1.2
294	dl	1.7	final void checkForComodification() {
295			if (modCount != expectedModCount)
296			throw new ConcurrentModificationException();
297			}
298	tim	1.2	}
299
300			/**
301			* Returns the number of elements in this priority queue.
302	tim	1.10	*
303	tim	1.2	* @return the number of elements in this priority queue.
304			*/
305	tim	1.1	public int size() {
306	tim	1.2	return size;
307	tim	1.1	}
308	tim	1.2
309			/**
310			* Remove all elements from the priority queue.
311			*/
312			public void clear() {
313			modCount++;
314
315			// Null out element references to prevent memory leak
316			for (int i=1; i<=size; i++)
317			queue[i] = null;
318
319			size = 0;
320			}
321
322			/**
323			* Removes and returns the ith element from queue. Recall
324			* that queue is one-based, so 1 <= i <= size.
325			*
326			* XXX: Could further special-case i==size, but is it worth it?
327			* XXX: Could special-case i==0, but is it worth it?
328			*/
329			private E remove(int i) {
330			assert i <= size;
331			modCount++;
332
333	tim	1.16	E result = (E) queue[i];
334	tim	1.2	queue[i] = queue[size];
335			queue[size--] = null; // Drop extra ref to prevent memory leak
336			if (i <= size)
337			fixDown(i);
338			return result;
339	tim	1.1	}
340
341	tim	1.2	/**
342			* Establishes the heap invariant (described above) assuming the heap
343			* satisfies the invariant except possibly for the leaf-node indexed by k
344			* (which may have a nextExecutionTime less than its parent's).
345			*
346			* This method functions by "promoting" queue[k] up the hierarchy
347			* (by swapping it with its parent) repeatedly until queue[k]
348			* is greater than or equal to its parent.
349			*/
350			private void fixUp(int k) {
351			if (comparator == null) {
352			while (k > 1) {
353			int j = k >> 1;
354	tim	1.16	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
355	tim	1.2	break;
356	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
357	tim	1.2	k = j;
358			}
359			} else {
360			while (k > 1) {
361			int j = k >> 1;
362	tim	1.16	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
363	tim	1.2	break;
364	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
365	tim	1.2	k = j;
366			}
367			}
368			}
369
370			/**
371			* Establishes the heap invariant (described above) in the subtree
372			* rooted at k, which is assumed to satisfy the heap invariant except
373			* possibly for node k itself (which may be greater than its children).
374			*
375			* This method functions by "demoting" queue[k] down the hierarchy
376			* (by swapping it with its smaller child) repeatedly until queue[k]
377			* is less than or equal to its children.
378			*/
379			private void fixDown(int k) {
380			int j;
381			if (comparator == null) {
382			while ((j = k << 1) <= size) {
383	tim	1.16	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
384	tim	1.2	j++; // j indexes smallest kid
385	tim	1.16	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
386	tim	1.2	break;
387	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
388	tim	1.2	k = j;
389			}
390			} else {
391			while ((j = k << 1) <= size) {
392	tim	1.16	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
393	tim	1.2	j++; // j indexes smallest kid
394	tim	1.16	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
395	tim	1.2	break;
396	tim	1.16	Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
397	tim	1.2	k = j;
398			}
399			}
400			}
401
402	tim	1.16	public Comparator<? super E> comparator() {
403	tim	1.2	return comparator;
404			}
405	dl	1.5
406			/**
407			* Save the state of the instance to a stream (that
408			* is, serialize it).
409			*
410			* @serialData The length of the array backing the instance is
411			* emitted (int), followed by all of its elements (each an
412			* <tt>Object</tt>) in the proper order.
413	dl	1.7	* @param s the stream
414	dl	1.5	*/
415			private synchronized void writeObject(java.io.ObjectOutputStream s)
416			throws java.io.IOException{
417	dl	1.7	// Write out element count, and any hidden stuff
418			s.defaultWriteObject();
419	dl	1.5
420			// Write out array length
421			s.writeInt(queue.length);
422
423	dl	1.7	// Write out all elements in the proper order.
424			for (int i=0; i<size; i++)
425	dl	1.5	s.writeObject(queue[i]);
426			}
427
428			/**
429			* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
430			* deserialize it).
431	dl	1.7	* @param s the stream
432	dl	1.5	*/
433			private synchronized void readObject(java.io.ObjectInputStream s)
434			throws java.io.IOException, ClassNotFoundException {
435	dl	1.7	// Read in size, and any hidden stuff
436			s.defaultReadObject();
437	dl	1.5
438			// Read in array length and allocate array
439			int arrayLength = s.readInt();
440	tim	1.16	queue = new Object[arrayLength];
441	dl	1.5
442	dl	1.7	// Read in all elements in the proper order.
443			for (int i=0; i<size; i++)
444	tim	1.16	queue[i] = s.readObject();
445	dl	1.5	}
446
447	tim	1.1	}
448	dholmes	1.11