--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/14 21:30:45 1.1 +++ jsr166/src/main/java/util/PriorityQueue.java 2005/11/22 11:44:47 1.52 @@ -1,64 +1,707 @@ -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. + */ -import java.util.*; +package java.util; +import java.util.*; // for javadoc (till 6280605 is fixed) /** - * An unbounded (resizable) priority queue based on a priority - * heap.The take operation returns the least element with respect to - * the given ordering. (If more than one element is tied for least - * value, one of them is arbitrarily chosen to be returned -- no - * guarantees are made for ordering across ties.) Ordering follows the - * java.util.Collection conventions: Either the elements must be - * Comparable, or a Comparator must be supplied. Comparison failures - * throw ClassCastExceptions during insertions and extractions. - **/ -public class PriorityQueue extends AbstractCollection implements Queue { - public PriorityQueue(int initialCapacity) {} - public PriorityQueue(int initialCapacity, Comparator comparator) {} - - public PriorityQueue(int initialCapacity, Collection initialElements) {} - - public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {} - - public boolean add(E x) { - return false; + * 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. + * + *

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. + * + *

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()). + * + *

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, + * 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). + * + *

This class is a member of the + * + * 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 java.io.Serializable { + + private static final long serialVersionUID = -7720805057305804111L; + + 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 comparator; + + /** + * The number of times this priority queue has been + * structurally modified. See AbstractList for gory details. + */ + private transient int modCount = 0; + + /** + * 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 + * {@linkplain Comparable natural ordering}. + * + * @param initialCapacity the initial capacity for this priority queue + * @throws IllegalArgumentException if initialCapacity is less + * than 1 + */ + public PriorityQueue(int initialCapacity) { + this(initialCapacity, null); } - public boolean offer(E x) { - return false; + + /** + * 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 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) { + if (initialCapacity < 1) + throw new IllegalArgumentException(); + this.queue = new Object[initialCapacity + 1]; + this.comparator = comparator; } - public boolean remove(Object x) { - return false; + + /** + * Common code to initialize underlying queue array across + * constructors below. + */ + private void initializeArray(Collection 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]; } - public E remove() { - return null; + /** + * 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(); + } } - public Iterator iterator() { - return null; + + /** + * 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(); } - public E element() { - return null; + /** + * 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); + } } - public E poll() { - return null; + + /** + * 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); + } + + /** + * 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); + } + + /** + * 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); } + + /** + * Inserts the specified element into this priority queue. + * + * @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 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 + if (size >= queue.length) + grow(size); + + queue[size] = e; + fixUp(size); + return true; + } + public E peek() { - return null; + if (size == 0) + return null; + return (E) queue[1]; } - public boolean isEmpty() { - return false; + 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; } - public int size() { - return 0; + + /** + * 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 remove(Object o) { + int i = indexOf(o); + if (i == -1) + return false; + else { + removeAt(i); + return true; + } + } + + /** + * 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 contains(Object o) { + return indexOf(o) != -1; } + + /** + * 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 null; + return Arrays.copyOfRange(queue, 1, size+1); + } + + /** + * 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(); } - public T[] toArray(T[] array) { + private class Itr implements Iterator { + + /** + * 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, + * unless that element came from the forgetMeNot list. + * Reset to 0 if 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; + + /** + * 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 || forgetMeNot != null; + } + + public E next() { + checkForComodification(); + E result; + if (cursor <= size) { + result = (E) queue[cursor]; + lastRet = cursor++; + } + else if (forgetMeNot == null) + throw new NoSuchElementException(); + else { + int remaining = forgetMeNot.size(); + result = forgetMeNot.remove(remaining - 1); + if (remaining == 1) + forgetMeNot = null; + lastRet = 0; + lastRetElt = result; + } + return result; + } + + public void remove() { + checkForComodification(); + + 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; + } + + final void checkForComodification() { + if (modCount != expectedModCount) + throw new ConcurrentModificationException(); + } + } + + public int size() { + return size; + } + + /** + * Removes all of the elements from this priority queue. + * The queue will be empty after this call returns. + */ + public void clear() { + modCount++; + + // Null out element references to prevent memory leak + for (int i=1; i<=size; i++) + queue[i] = null; + + 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.) + * + * 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 removeAt(int i) { + assert i > 0 && i <= size; + modCount++; + + E moved = (E) queue[size]; + queue[i] = moved; + queue[size--] = null; // Drop extra ref to prevent memory leak + if (i <= size) { + fixDown(i); + if (queue[i] == moved) { + fixUp(i); + if (queue[i] != moved) + return moved; + } + } return null; } + /** + * 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((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 && (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) + break; + Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } else { + 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; + Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } + } + + /** + * 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; + } + + /** + * 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 + * Object) in the proper order. + * @param s the stream + */ + private 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=1; i<=size; i++) + s.writeObject(queue[i]); + } + + /** + * Reconstitute the PriorityQueue instance from a stream + * (that is, deserialize it). + * @param s the stream + */ + private 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=1; i<=size; i++) + queue[i] = (E) s.readObject(); + } + }