--- jsr166/src/main/java/util/PriorityQueue.java 2006/02/07 20:54:24 1.61 +++ jsr166/src/main/java/util/PriorityQueue.java 2007/01/07 07:38:27 1.66 @@ -1,27 +1,27 @@ /* * %W% %E% * - * Copyright 2006 Sun Microsystems, Inc. All rights reserved. + * Copyright 2007 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util; /** - * An unbounded priority {@linkplain Queue queue} based on a priority - * heap. The elements of the priority queue are ordered according to - * their {@linkplain Comparable natural ordering}, or by a {@link - * Comparator} provided at queue construction time, depending on which - * constructor is used. A priority queue does not permit - * null elements. A priority queue relying on natural - * ordering also does not permit insertion of non-comparable objects - * (doing so may result in ClassCastException). + * An unbounded priority {@linkplain Queue queue} based on a priority heap. + * The elements of the priority queue are ordered according to their + * {@linkplain Comparable natural ordering}, or by a {@link Comparator} + * provided at queue construction time, depending on which constructor is + * used. A priority queue does not permit {@code null} elements. + * A priority queue relying on natural ordering also does not permit + * insertion of non-comparable objects (doing so may result in + * {@code ClassCastException}). * *

The head 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 -- ties are - * broken arbitrarily. The queue retrieval operations poll, - * remove, peek, and element access the + * broken arbitrarily. The queue retrieval operations {@code poll}, + * {@code remove}, {@code peek}, and {@code element} access the * element at the head of the queue. * *

A priority queue is unbounded, but has an internal @@ -36,27 +36,28 @@ package java.util; * Iterator} interfaces. The Iterator provided in method {@link * #iterator()} is not guaranteed to traverse the elements of * the priority queue in any particular order. If you need ordered - * traversal, consider using Arrays.sort(pq.toArray()). + * traversal, consider using {@code Arrays.sort(pq.toArray())}. * *

Note that this implementation is not synchronized. - * Multiple threads should not access a PriorityQueue - * instance concurrently if any of the threads modifies the list - * structurally. Instead, use the thread-safe {@link + * Multiple threads should not access a {@code PriorityQueue} + * instance concurrently if any of the threads modifies the queue. + * Instead, use the thread-safe {@link * java.util.concurrent.PriorityBlockingQueue} class. * - *

Implementation note: this implementation provides O(log(n)) time - * for the insertion methods (offer, poll, - * remove() and add) methods; linear time for the - * remove(Object) and contains(Object) methods; and - * constant time for the retrieval methods (peek, - * element, and size). + *

Implementation note: this implementation provides + * O(log(n)) time for the enqueing and dequeing methods + * ({@code offer}, {@code poll}, {@code remove()} and {@code add}); + * linear time for the {@code remove(Object)} and {@code contains(Object)} + * methods; and constant time for the retrieval methods + * ({@code peek}, {@code element}, and {@code size}). * *

This class is a member of the - * + * * Java Collections Framework. + * * @since 1.5 - * @version 1.8, 08/27/05 - * @author Josh Bloch + * @version %I%, %G% + * @author Josh Bloch, Doug Lea * @param the type of elements held in this collection */ public class PriorityQueue extends AbstractQueue @@ -94,7 +95,7 @@ public class PriorityQueue extends Ab private transient int modCount = 0; /** - * Creates a PriorityQueue with the default initial + * Creates a {@code PriorityQueue} with the default initial * capacity (11) that orders its elements according to their * {@linkplain Comparable natural ordering}. */ @@ -103,27 +104,27 @@ public class PriorityQueue extends Ab } /** - * Creates a PriorityQueue with the specified initial + * Creates a {@code PriorityQueue} with the specified initial * capacity that orders its elements according to their * {@linkplain Comparable natural ordering}. * * @param initialCapacity the initial capacity for this priority queue - * @throws IllegalArgumentException if initialCapacity is less - * than 1 + * @throws IllegalArgumentException if {@code initialCapacity} is less + * than 1 */ public PriorityQueue(int initialCapacity) { this(initialCapacity, null); } /** - * Creates a PriorityQueue with the specified initial capacity + * Creates a {@code PriorityQueue} 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 that will be used to order - * this priority queue. If null, the natural - * ordering of the elements will be used. - * @throws IllegalArgumentException if initialCapacity is + * @param comparator the comparator that will be used to order this + * priority queue. If {@code null}, the {@linkplain Comparable + * natural ordering} of the elements will be used. + * @throws IllegalArgumentException if {@code initialCapacity} is * less than 1 */ public PriorityQueue(int initialCapacity, @@ -137,12 +138,12 @@ public class PriorityQueue extends Ab } /** - * Creates a PriorityQueue containing the elements in the - * specified collection. If the specified collection is an - * instance of a {@link java.util.SortedSet} or is another - * PriorityQueue, the priority queue will be ordered - * according to the same ordering. Otherwise, this priority queue - * will be ordered according to the natural ordering of its elements. + * Creates a {@code PriorityQueue} containing the elements in the + * specified collection. If the specified collection is an instance of + * a {@link SortedSet} or is another {@code PriorityQueue}, this + * priority queue will be ordered according to the same ordering. + * Otherwise, this priority queue will be ordered according to the + * {@linkplain Comparable natural ordering} of its elements. * * @param c the collection whose elements are to be placed * into this priority queue @@ -167,15 +168,15 @@ public class PriorityQueue extends Ab } /** - * Creates a PriorityQueue containing the elements in the + * Creates a {@code PriorityQueue} containing the elements in the * specified priority queue. This priority queue will be * ordered according to the same ordering as the given priority * queue. * * @param c the priority queue whose elements are to be placed * into this priority queue - * @throws ClassCastException if elements of c cannot be - * compared to one another according to c's + * @throws ClassCastException if elements of {@code c} cannot be + * compared to one another according to {@code c}'s * ordering * @throws NullPointerException if the specified priority queue or any * of its elements are null @@ -186,12 +187,12 @@ public class PriorityQueue extends Ab } /** - * Creates a PriorityQueue containing the elements in the - * specified sorted set. This priority queue will be ordered + * Creates a {@code PriorityQueue} containing the elements in the + * specified sorted set. This priority queue will be ordered * according to the same ordering as the given sorted set. * * @param c the sorted set whose elements are to be placed - * into this priority queue. + * into this priority queue * @throws ClassCastException if elements of the specified sorted * set cannot be compared to one another according to the * sorted set's ordering @@ -204,7 +205,8 @@ public class PriorityQueue extends Ab } /** - * Initialize queue array with elements from the given Collection. + * Initializes queue array with elements from the given Collection. + * * @param c the collection */ private void initFromCollection(Collection c) { @@ -239,7 +241,7 @@ public class PriorityQueue extends Ab /** * Inserts the specified element into this priority queue. * - * @return true (as specified by {@link Collection#add}) + * @return {@code true} (as specified by {@link Collection#add}) * @throws ClassCastException if the specified element cannot be * compared with elements currently in this priority queue * according to the priority queue's ordering @@ -252,7 +254,7 @@ public class PriorityQueue extends Ab /** * Inserts the specified element into this priority queue. * - * @return true (as specified by {@link Queue#offer}) + * @return {@code true} (as specified by {@link Queue#offer}) * @throws ClassCastException if the specified element cannot be * compared with elements currently in this priority queue * according to the priority queue's ordering @@ -290,13 +292,14 @@ public class PriorityQueue extends Ab /** * Removes a single instance of the specified element from this queue, - * if it is present. More formally, removes an element e such - * that o.equals(e), if this queue contains one or more such - * elements. Returns true if this queue contained the specified element - * (or equivalently, if this queue changed as a result of the call). + * if it is present. More formally, removes an element {@code e} such + * that {@code o.equals(e)}, if this queue contains one or more such + * elements. Returns {@code true} if and only if this queue contained + * the specified element (or equivalently, if this queue changed as a + * result of the call). * * @param o element to be removed from this queue, if present - * @return true if this queue changed as a result of the call + * @return {@code true} if this queue changed as a result of the call */ public boolean remove(Object o) { int i = indexOf(o); @@ -313,7 +316,7 @@ public class PriorityQueue extends Ab * Needed by iterator.remove. * * @param o element to be removed from this queue, if present - * @return true if removed + * @return {@code true} if removed */ boolean removeEq(Object o) { for (int i = 0; i < size; i++) { @@ -326,25 +329,28 @@ public class PriorityQueue extends Ab } /** - * Returns true if this queue contains the specified element. - * More formally, returns true if and only if this queue contains - * at least one element e such that o.equals(e). + * Returns {@code true} if this queue contains the specified element. + * More formally, returns {@code true} if and only if this queue contains + * at least one element {@code e} such that {@code o.equals(e)}. * * @param o object to be checked for containment in this queue - * @return true if this queue contains the specified element + * @return {@code true} if this queue contains the specified element */ public boolean contains(Object o) { return indexOf(o) != -1; } /** - * Returns an array containing all of the elements in this queue, + * Returns an array containing all of the elements in this queue. * The elements are in no particular order. * *

The returned array will be "safe" in that no references to it are - * maintained by this list. (In other words, this method must allocate + * maintained by this queue. (In other words, this method must allocate * a new array). The caller is thus free to modify the returned array. * + *

This method acts as bridge between array-based and collection-based + * APIs. + * * @return an array containing all of the elements in this queue */ public Object[] toArray() { @@ -352,24 +358,37 @@ public class PriorityQueue extends Ab } /** - * Returns an array containing all of the elements in this queue. - * The elements are in no particular order. The runtime type of - * the returned array is that of the specified array. If the queue - * fits in the specified array, it is returned therein. - * Otherwise, a new array is allocated with the runtime type of - * the specified array and the size of this queue. + * Returns an array containing all of the elements in this queue; the + * runtime type of the returned array is that of the specified array. + * The returned array elements are in no particular order. + * If the queue fits in the specified array, it is returned therein. + * Otherwise, a new array is allocated with the runtime type of the + * specified array and the size of this queue. * *

If the queue fits in the specified array with room to spare * (i.e., the array has more elements than the queue), the element in * the array immediately following the end of the collection is set to - * null. (This is useful in determining the length of the - * queue only if the caller knows that the queue does not contain - * any null elements.) + * {@code null}. + * + *

Like the {@link #toArray()} method, this method acts as bridge between + * array-based and collection-based APIs. Further, this method allows + * precise control over the runtime type of the output array, and may, + * under certain circumstances, be used to save allocation costs. + * + *

Suppose x is a queue known to contain only strings. + * The following code can be used to dump the queue into a newly + * allocated array of String: + * + * 

+     *     String[] y = x.toArray(new String[0]);
+ * + * Note that toArray(new Object[0]) is identical in function to + * toArray(). * * @param a the array into which the elements of the queue are to * be stored, if it is big enough; otherwise, a new array of the * same runtime type is allocated for this purpose. - * @return an array containing the elements of the queue + * @return an array containing all of the elements in this queue * @throws ArrayStoreException if the runtime type of the specified array * is not a supertype of the runtime type of every element in * this queue @@ -418,7 +437,7 @@ public class PriorityQueue extends Ab * after we've completed the "normal" iteration. * * We expect that most iterations, even those involving removals, - * will not use need to store elements in this field. + * will not need to store elements in this field. */ private ArrayDeque forgetMeNot = null; @@ -430,7 +449,7 @@ public class PriorityQueue extends Ab /** * The modCount value that the iterator believes that the backing - * List should have. If this expectation is violated, the iterator + * Queue should have. If this expectation is violated, the iterator * has detected concurrent modification. */ private int expectedModCount = modCount; @@ -457,8 +476,6 @@ public class PriorityQueue extends Ab public void remove() { if (expectedModCount != modCount) throw new ConcurrentModificationException(); - if (lastRet == -1 && lastRetElt == null) - throw new IllegalStateException(); if (lastRet != -1) { E moved = PriorityQueue.this.removeAt(lastRet); lastRet = -1; @@ -469,13 +486,14 @@ public class PriorityQueue extends Ab forgetMeNot = new ArrayDeque(); forgetMeNot.add(moved); } - } else { + } else if (lastRetElt != null) { PriorityQueue.this.removeEq(lastRetElt); lastRetElt = null; - } + } else { + throw new IllegalStateException(); + } expectedModCount = modCount; } - } public int size() { @@ -498,8 +516,8 @@ public class PriorityQueue extends Ab return null; int s = --size; modCount++; - E result = (E)queue[0]; - E x = (E)queue[s]; + E result = (E) queue[0]; + E x = (E) queue[s]; queue[s] = null; if (s != 0) siftDown(0, x); @@ -516,7 +534,7 @@ public class PriorityQueue extends Ab * i. Under these circumstances, this method returns the element * that was previously at the end of the list and is now at some * position before i. This fact is used by iterator.remove so as to - * avoid missing traverseing elements. + * avoid missing traversing elements. */ private E removeAt(int i) { assert i >= 0 && i < size; @@ -561,7 +579,7 @@ public class PriorityQueue extends Ab while (k > 0) { int parent = (k - 1) >>> 1; Object e = queue[parent]; - if (key.compareTo((E)e) >= 0) + if (key.compareTo((E) e) >= 0) break; queue[k] = e; k = parent; @@ -573,7 +591,7 @@ public class PriorityQueue extends Ab while (k > 0) { int parent = (k - 1) >>> 1; Object e = queue[parent]; - if (comparator.compare(x, (E)e) >= 0) + if (comparator.compare(x, (E) e) >= 0) break; queue[k] = e; k = parent; @@ -604,9 +622,9 @@ public class PriorityQueue extends Ab Object c = queue[child]; int right = child + 1; if (right < size && - ((Comparable)c).compareTo((E)queue[right]) > 0) + ((Comparable) c).compareTo((E) queue[right]) > 0) c = queue[child = right]; - if (key.compareTo((E)c) <= 0) + if (key.compareTo((E) c) <= 0) break; queue[k] = c; k = child; @@ -621,9 +639,9 @@ public class PriorityQueue extends Ab Object c = queue[child]; int right = child + 1; if (right < size && - comparator.compare((E)c, (E)queue[right]) > 0) + comparator.compare((E) c, (E) queue[right]) > 0) c = queue[child = right]; - if (comparator.compare(x, (E)c) <= 0) + if (comparator.compare(x, (E) c) <= 0) break; queue[k] = c; k = child; @@ -637,29 +655,29 @@ public class PriorityQueue extends Ab */ private void heapify() { for (int i = (size >>> 1) - 1; i >= 0; i--) - siftDown(i, (E)queue[i]); + siftDown(i, (E) queue[i]); } /** * Returns the comparator used to order the elements in this - * queue, or null if this queue is sorted according to + * queue, or {@code null} if this queue is sorted according to * the {@linkplain Comparable natural ordering} of its elements. * * @return the comparator used to order this queue, or - * null if this queue is sorted according to the - * natural ordering of its elements. + * {@code null} if this queue is sorted according to the + * natural ordering of its elements */ public Comparator comparator() { return comparator; } /** - * Save the state of the instance to a stream (that - * is, serialize it). + * Saves the state of the instance to a stream (that + * is, serializes it). * * @serialData The length of the array backing the instance is - * emitted (int), followed by all of its elements (each an - * Object) in the proper order. + * emitted (int), followed by all of its elements + * (each an {@code Object}) in the proper order. * @param s the stream */ private void writeObject(java.io.ObjectOutputStream s) @@ -667,18 +685,18 @@ public class PriorityQueue extends Ab // Write out element count, and any hidden stuff s.defaultWriteObject(); - // Write out array length - // For compatibility with 1.5 version, must be at least 2. - s.writeInt(Math.max(2, queue.length)); + // Write out array length, for compatibility with 1.5 version + s.writeInt(Math.max(2, size + 1)); - // Write out all elements in the proper order. - for (int i=0; iPriorityQueue instance from a stream - * (that is, deserialize it). + * Reconstitutes the {@code PriorityQueue} instance from a stream + * (that is, deserializes it). + * * @param s the stream */ private void readObject(java.io.ObjectInputStream s) @@ -686,13 +704,17 @@ public class PriorityQueue extends Ab // 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