--- jsr166/src/main/java/util/PriorityQueue.java 2003/08/05 06:49:51 1.21 +++ jsr166/src/main/java/util/PriorityQueue.java 2005/11/22 11:44:47 1.52 @@ -1,31 +1,49 @@ - package java.util; +/* + * @(#)PriorityQueue.java 1.8 05/08/27 + * + * Copyright 2005 Sun Microsystems, Inc. All rights reserved. + * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. + */ + +package java.util; +import java.util.*; // for javadoc (till 6280605 is fixed) /** - * 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 natural order (see {@link Comparable}), or - * according to a {@link java.util.Comparator}, depending on which - * constructor is used. - *

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. A priority queue does not permit - * null elements. + * 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). + * + *

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 + * element at the head of the queue. * - *

The {@link #remove()} and {@link #poll()} methods remove and - * return the head of the queue. + *

A priority queue is unbounded, but has an internal + * capacity governing the size of an 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 queue, its capacity + * grows automatically. The details of the growth policy are not + * specified. * - *

The {@link #element()} and {@link #peek()} methods return, but do - * not delete, the head of the queue. + *

This class and its iterator implement all of the + * optional methods of the {@link Collection} and {@link + * 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()). * - *

A priority queue has a capacity. 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. + *

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 + * java.util.concurrent.PriorityBlockingQueue} class. * *

Implementation note: this implementation provides O(log(n)) time * for the insertion methods (offer, poll, @@ -38,10 +56,14 @@ * * Java Collections Framework. * @since 1.5 + * @version 1.8, 08/27/05 * @author Josh Bloch + * @param the type of elements held in this collection */ public class PriorityQueue extends AbstractQueue - implements Sorted, Queue, java.io.Serializable { + implements java.io.Serializable { + + private static final long serialVersionUID = -7720805057305804111L; private static final int DEFAULT_INITIAL_CAPACITY = 11; @@ -78,20 +100,22 @@ public class PriorityQueue extends Ab private transient int modCount = 0; /** - * Creates a PriorityQueue with the default initial capacity - * (11) that orders its elements according to their natural - * ordering (using Comparable.) + * Creates a PriorityQueue with the default initial + * capacity (11) that orders its elements according to their + * {@linkplain Comparable natural ordering}. */ public PriorityQueue() { this(DEFAULT_INITIAL_CAPACITY, null); } /** - * Creates a PriorityQueue with the specified initial capacity - * that orders its elements according to their natural ordering - * (using Comparable.) + * Creates a 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. + * @param initialCapacity the initial capacity for this priority queue + * @throws IllegalArgumentException if initialCapacity is less + * than 1 */ public PriorityQueue(int initialCapacity) { this(initialCapacity, null); @@ -101,14 +125,15 @@ public class PriorityQueue extends Ab * Creates a 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 used to order this priority queue. - * If null then the order depends on the elements' natural - * ordering. - * @throws IllegalArgumentException if initialCapacity is less - * than 1 + * @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 + * less than 1 */ - public PriorityQueue(int initialCapacity, Comparator comparator) { + public PriorityQueue(int initialCapacity, + Comparator comparator) { if (initialCapacity < 1) throw new IllegalArgumentException(); this.queue = new Object[initialCapacity + 1]; @@ -116,27 +141,10 @@ public class PriorityQueue extends Ab } /** - * Creates a PriorityQueue 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 - * Sorted, 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 c or any element within it - * is null + * Common code to initialize underlying queue array across + * constructors below. */ - public PriorityQueue(Collection c) { + private void initializeArray(Collection c) { int sz = c.size(); int initialCapacity = (int)Math.min((sz * 110L) / 100, Integer.MAX_VALUE - 1); @@ -144,108 +152,276 @@ public class PriorityQueue extends Ab initialCapacity = 1; this.queue = new Object[initialCapacity + 1]; + } - if (c instanceof Sorted) { - comparator = (Comparator)((Sorted)c).comparator(); + /** + * Initially fill elements of the queue array under the + * knowledge that it is sorted or is another PQ, in which + * case we can just place the elements in the order presented. + */ + private void fillFromSorted(Collection c) { + for (Iterator i = c.iterator(); i.hasNext(); ) { + int k = ++size; + if (k >= queue.length) + grow(k); + queue[k] = i.next(); + } + } + + /** + * Initially fill elements of the queue array that is not to our knowledge + * sorted, so we must rearrange the elements to guarantee the heap + * invariant. + */ + private void fillFromUnsorted(Collection c) { + for (Iterator i = c.iterator(); i.hasNext(); ) { + int k = ++size; + if (k >= queue.length) + grow(k); + queue[k] = i.next(); + } + heapify(); + } + + /** + * Creates a PriorityQueue 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 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. + * + * @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 the specified collection or any + * of its elements are null + */ + public PriorityQueue(Collection c) { + initializeArray(c); + if (c instanceof SortedSet) { + SortedSet s = (SortedSet)c; + comparator = (Comparator)s.comparator(); + fillFromSorted(s); + } else if (c instanceof PriorityQueue) { + PriorityQueue s = (PriorityQueue) c; + comparator = (Comparator)s.comparator(); + fillFromSorted(s); } else { comparator = null; + fillFromUnsorted(c); } + } + + /** + * Creates a PriorityQueue containing the elements in the + * specified priority queue. The priority queue has an initial + * capacity of 110% of the size of the specified priority queue or + * 1 if the priority queue is empty. 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 + * ordering + * @throws NullPointerException if the specified priority queue or any + * of its elements are null + */ + public PriorityQueue(PriorityQueue c) { + initializeArray(c); + comparator = (Comparator)c.comparator(); + fillFromSorted(c); + } - for (Iterator i = c.iterator(); i.hasNext(); ) - add(i.next()); + /** + * Creates a PriorityQueue containing the elements in the + * specified sorted set. The priority queue has an initial + * capacity of 110% of the size of the specified sorted set or 1 + * if the sorted set is empty. 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. + * @throws ClassCastException if elements of the specified sorted + * set cannot be compared to one another according to the + * sorted set's ordering + * @throws NullPointerException if the specified sorted set or any + * of its elements are null + */ + public PriorityQueue(SortedSet c) { + initializeArray(c); + comparator = (Comparator)c.comparator(); + fillFromSorted(c); } - // Queue Methods + /** + * Resize array, if necessary, to be able to hold given index. + */ + private void grow(int index) { + int newlen = queue.length; + if (index < newlen) // don't need to grow + return; + if (index == Integer.MAX_VALUE) + throw new OutOfMemoryError(); + while (newlen <= index) { + if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow + newlen = Integer.MAX_VALUE; + else + newlen <<= 2; + } + queue = Arrays.copyOf(queue, newlen); + } /** - * Add the specified element to this priority queue. + * Inserts the specified element into this priority queue. * - * @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. + * @return 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 + * @throws NullPointerException if the specified element is null */ - public boolean offer(E o) { - if (o == null) + public boolean add(E e) { + return offer(e); + } + + /** + * Inserts the specified element into this priority queue. + * + * @return 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 + * @throws NullPointerException if the specified element is null + */ + public boolean offer(E e) { + if (e == 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; - } + if (size >= queue.length) + grow(size); - queue[size] = o; + queue[size] = e; fixUp(size); return true; } - public E poll() { + public E peek() { 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 + private int indexOf(Object o) { + if (o == null) + return -1; + for (int i = 1; i <= size; i++) + if (o.equals(queue[i])) + return i; + return -1; + } /** - * @throws NullPointerException if the specified element is null. - * @throws ClassCastException if the specified element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. + * 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). + * + * @param o element to be removed from this queue, if present + * @return true if this queue changed as a result of the call */ - public boolean add(E o) { - return super.add(o); + public boolean remove(Object o) { + int i = indexOf(o); + if (i == -1) + return false; + else { + removeAt(i); + return true; + } } /** - * @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 c or any element in c - * is null + * 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). + * + * @param o object to be checked for containment in this queue + * @return true if this queue contains the specified element */ - public boolean addAll(Collection c) { - return super.addAll(c); + public boolean contains(Object o) { + return indexOf(o) != -1; } - public boolean remove(Object o) { - if (o == null) - return false; + /** + * 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 + * a new array). The caller is thus free to modify the returned array. + * + * @return an array containing all of the elements in this queue. + */ + public Object[] toArray() { + return Arrays.copyOfRange(queue, 1, size+1); + } - if (comparator == null) { - for (int i = 1; i <= size; i++) { - if (((Comparable)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; + /** + * 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. + * + *

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.) + * + * @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 + * @throws ArrayStoreException if the runtime type of the specified array + * is not a supertype of the runtime type of every element in + * this queue + * @throws NullPointerException if the specified array is null + */ + public T[] toArray(T[] a) { + if (a.length < size) + // Make a new array of a's runtime type, but my contents: + return (T[]) Arrays.copyOfRange(queue, 1, size+1, a.getClass()); + System.arraycopy(queue, 1, a, 0, size); + if (a.length > size) + a[size] = null; + return a; } + /** + * Returns an iterator over the elements in this queue. The iterator + * does not return the elements in any particular order. + * + * @return an iterator over the elements in this queue + */ public Iterator iterator() { return new Itr(); } private class Itr implements Iterator { + /** * Index (into queue array) of element to be returned by * subsequent call to next. @@ -253,9 +429,9 @@ public class PriorityQueue extends Ab 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. + * Index of element returned by most recent call to next, + * unless that element came from the forgetMeNot list. + * Reset to 0 if element is deleted by a call to remove. */ private int lastRet = 0; @@ -266,28 +442,69 @@ public class PriorityQueue extends Ab */ private int expectedModCount = modCount; + /** + * A list of elements that were moved from the unvisited portion of + * the heap into the visited portion as a result of "unlucky" element + * removals during the iteration. (Unlucky element removals are those + * that require a fixup instead of a fixdown.) We must visit all of + * the elements in this list to complete the iteration. We do this + * 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. + */ + private ArrayList forgetMeNot = null; + + /** + * Element returned by the most recent call to next iff that + * element was drawn from the forgetMeNot list. + */ + private Object lastRetElt = null; + public boolean hasNext() { - return cursor <= size; + return cursor <= size || forgetMeNot != null; } public E next() { checkForComodification(); - if (cursor > size) + E result; + if (cursor <= size) { + result = (E) queue[cursor]; + lastRet = cursor++; + } + else if (forgetMeNot == null) throw new NoSuchElementException(); - E result = (E) queue[cursor]; - lastRet = cursor++; + else { + int remaining = forgetMeNot.size(); + result = forgetMeNot.remove(remaining - 1); + if (remaining == 1) + forgetMeNot = null; + lastRet = 0; + lastRetElt = result; + } return result; } public void remove() { - if (lastRet == 0) - throw new IllegalStateException(); checkForComodification(); - PriorityQueue.this.remove(lastRet); - if (lastRet < cursor) - cursor--; - lastRet = 0; + if (lastRet != 0) { + E moved = PriorityQueue.this.removeAt(lastRet); + lastRet = 0; + if (moved == null) { + cursor--; + } else { + if (forgetMeNot == null) + forgetMeNot = new ArrayList(); + forgetMeNot.add(moved); + } + } else if (lastRetElt != null) { + PriorityQueue.this.remove(lastRetElt); + lastRetElt = null; + } else { + throw new IllegalStateException(); + } + expectedModCount = modCount; } @@ -297,17 +514,13 @@ public class PriorityQueue extends Ab } } - /** - * 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. + * Removes all of the elements from this priority queue. + * The queue will be empty after this call returns. */ public void clear() { modCount++; @@ -319,23 +532,49 @@ public class PriorityQueue extends Ab size = 0; } + public E poll() { + if (size == 0) + return null; + modCount++; + + E result = (E) queue[1]; + queue[1] = queue[size]; + queue[size--] = null; // Drop extra ref to prevent memory leak + if (size > 1) + fixDown(1); + + return result; + } + /** - * Removes and returns the ith element from queue. Recall - * that queue is one-based, so 1 <= i <= size. + * 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? + * Normally this method leaves the elements at positions from 1 up to i-1, + * inclusive, untouched. Under these circumstances, it returns null. + * Occasionally, in order to maintain the heap invariant, it must move + * the last element of the list to some index in the range [2, i-1], + * and move the element previously at position (i/2) to position i. + * Under these circumstances, this method returns the element that was + * previously at the end of the list and is now at some position between + * 2 and i-1 inclusive. */ - private E remove(int i) { - assert i <= size; + private E removeAt(int i) { + assert i > 0 && i <= size; modCount++; - E result = (E) queue[i]; - queue[i] = queue[size]; + E moved = (E) queue[size]; + queue[i] = moved; queue[size--] = null; // Drop extra ref to prevent memory leak - if (i <= size) + if (i <= size) { fixDown(i); - return result; + if (queue[i] == moved) { + fixUp(i); + if (queue[i] != moved) + return moved; + } + } + return null; } /** @@ -351,14 +590,14 @@ public class PriorityQueue extends Ab if (comparator == null) { while (k > 1) { int j = k >> 1; - if (((Comparable)queue[j]).compareTo((E)queue[k]) <= 0) + if (((Comparable)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; + 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; @@ -379,17 +618,20 @@ public class PriorityQueue extends Ab private void fixDown(int k) { int j; if (comparator == null) { - while ((j = k << 1) <= size) { - if (j)queue[j]).compareTo((E)queue[j+1]) > 0) + while ((j = k << 1) <= size && (j > 0)) { + if (j)queue[j]).compareTo((E)queue[j+1]) > 0) j++; // j indexes smallest kid - if (((Comparable)queue[k]).compareTo((E)queue[j]) <= 0) + + if (((Comparable)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) + while ((j = k << 1) <= size && (j > 0)) { + if (j 0) j++; // j indexes smallest kid if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) break; @@ -399,6 +641,24 @@ public class PriorityQueue extends Ab } } + /** + * Establishes the heap invariant (described above) in the entire tree, + * assuming nothing about the order of the elements prior to the call. + */ + private void heapify() { + for (int i = size/2; i >= 1; i--) + fixDown(i); + } + + /** + * Returns the comparator used to order the elements in this + * queue, or 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. + */ public Comparator comparator() { return comparator; } @@ -412,7 +672,7 @@ public class PriorityQueue extends Ab * Object) in the proper order. * @param s the stream */ - private synchronized void writeObject(java.io.ObjectOutputStream s) + private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException{ // Write out element count, and any hidden stuff s.defaultWriteObject(); @@ -421,16 +681,16 @@ public class PriorityQueue extends Ab s.writeInt(queue.length); // Write out all elements in the proper order. - for (int i=0; iArrayList instance from a stream (that is, - * deserialize it). + * Reconstitute the PriorityQueue instance from a stream + * (that is, deserialize it). * @param s the stream */ - private synchronized void readObject(java.io.ObjectInputStream s) + private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in size, and any hidden stuff s.defaultReadObject(); @@ -440,9 +700,8 @@ public class PriorityQueue extends Ab queue = new Object[arrayLength]; // Read in all elements in the proper order. - for (int i=0; i