--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/18 18:10:02 1.2
+++ jsr166/src/main/java/util/PriorityQueue.java 2003/08/25 23:47:01 1.32
@@ -1,57 +1,79 @@
package java.util;
-/*
- * Todo
- *
- * 1) Make it serializable.
- */
-
/**
- * An unbounded priority queue based on a priority heap. This queue orders
- * elements according to the order specified at creation time. This order is
- * specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
+ * An unbounded priority {@linkplain Queue 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 Comparator}, depending on which constructor is used.
- * The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
- * minimal element with respect to the specified ordering. If multiple
- * these elements are tied for least value, no guarantees are made as to
- * which of elements is returned.
+ * 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.
+ *
+ *
The {@link #remove()} and {@link #poll()} methods remove and
+ * return the head of the queue.
*
- *
Each priority queue has a capacity. The capacity is the size of
- * the array used to store the elements on the queue. It is always at least
- * as large as the queue size. As elements are added to a priority list,
- * its capacity grows automatically. The details of the growth policy are not
- * specified.
+ *
The {@link #element()} and {@link #peek()} methods return, but do
+ * not delete, the head of the queue.
*
- *
Implementation note: this implementation provides O(log(n)) time for
- * the offer, poll, remove() and add
- * methods; linear time for the remove(Object) and
- * contains methods; and constant time for the peek,
- * element, and size methods.
+ *
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.
+ *
+ *
The Iterator provided in method {@link #iterator()} is not
+ * guaranteed to traverse the elements of the PriorityQueue 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.BlockingPriorityQueue} 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
+ * @author Josh Bloch
*/
public class PriorityQueue extends AbstractQueue
- implements Queue
-{
+ implements Queue, 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
- * of n, d, n <= d.
+ * 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.
+ * The element with the lowest value is in queue[1], assuming the queue is
+ * nonempty. (A one-based array is used in preference to the traditional
+ * zero-based array to simplify parent and child calculations.)
*
* queue.length must be >= 2, even if size == 0.
*/
- private E[] queue;
+ private transient Object[] queue;
/**
* The number of elements in the priority queue.
@@ -62,149 +84,295 @@ public class PriorityQueue extends Ab
* The comparator, or null if priority queue uses elements'
* natural ordering.
*/
- private final Comparator comparator;
+ private final Comparator super E> comparator;
/**
* The number of times this priority queue has been
* structurally modified. See AbstractList for gory details.
*/
- private int modCount = 0;
+ private transient int modCount = 0;
/**
- * Create a new priority queue with the default initial capacity (11)
- * that orders its elements according to their natural ordering.
+ * Creates a PriorityQueue with the default initial capacity
+ * (11) that orders its elements according to their natural
+ * ordering (using Comparable).
*/
public PriorityQueue() {
- this(DEFAULT_INITIAL_CAPACITY);
+ this(DEFAULT_INITIAL_CAPACITY, null);
}
/**
- * Create a new priority queue with the specified initial capacity
- * that orders its elements according to their natural ordering.
+ * Creates a PriorityQueue with the specified initial capacity
+ * that orders its elements according to their natural ordering
+ * (using Comparable).
*
* @param initialCapacity the initial capacity for this priority queue.
+ * @throws IllegalArgumentException if initialCapacity is less
+ * than 1
*/
public PriorityQueue(int initialCapacity) {
this(initialCapacity, null);
}
/**
- * Create a new priority queue with the specified initial capacity (11)
+ * 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
*/
- public PriorityQueue(int initialCapacity, Comparator comparator) {
+ public PriorityQueue(int initialCapacity,
+ Comparator super E> comparator) {
if (initialCapacity < 1)
- initialCapacity = 1;
- queue = new E[initialCapacity + 1];
+ throw new IllegalArgumentException();
+ this.queue = new Object[initialCapacity + 1];
this.comparator = comparator;
}
/**
- * Create a new priority queue containing the elements in the specified
- * collection. The priority queue has an initial capacity of 110% of the
- * size of the specified collection. If the specified collection
- * implements the {@link Sorted} interface, the priority queue will be
- * sorted according to the same comparator, or according to its elements'
- * natural order if the collection is sorted according to its elements'
- * natural order. If the specified collection does not implement the
- * Sorted interface, the priority queue is ordered according to
- * its elements' natural order.
- *
- * @param initialElements the collection whose elements are to be placed
- * into this priority queue.
- * @throws ClassCastException if elements of the specified collection
- * cannot be compared to one another according to the priority
- * queue's ordering.
- * @throws NullPointerException if the specified collection or an
- * element of the specified collection is null.
+ * Common code to initialize underlying queue array across
+ * constructors below.
*/
- public PriorityQueue(Collection initialElements) {
- int sz = initialElements.size();
+ private void initializeArray(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;
- queue = new E[initialCapacity + 1];
- /* Commented out to compile with generics compiler
+ this.queue = new Object[initialCapacity + 1];
+ }
+
+ /**
+ * 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 without fixups.
+ */
+ private void fillFromSorted(Collection extends E> c) {
+ for (Iterator extends E> i = c.iterator(); i.hasNext(); )
+ queue[++size] = i.next();
+ }
+
+
+ /**
+ * Initially fill elements of the queue array that is
+ * not to our knowledge sorted, so we must add them
+ * one by one.
+ */
+ private void fillFromUnsorted(Collection extends E> c) {
+ for (Iterator extends E> i = c.iterator(); i.hasNext(); )
+ add(i.next());
+ }
- if (initialElements instanceof Sorted) {
- comparator = ((Sorted)initialElements).comparator();
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- queue[++size] = i.next();
+ /**
+ * 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 sorted
+ * according to the same comparator, or according to its elements'
+ * natural order if the collection is sorted according to its
+ * elements' natural order. Otherwise, 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
+ */
+ public PriorityQueue(Collection extends E> c) {
+ initializeArray(c);
+ if (c instanceof SortedSet) {
+ // @fixme double-cast workaround for compiler
+ SortedSet extends E> s = (SortedSet extends E>) (SortedSet)c;
+ comparator = (Comparator super E>)s.comparator();
+ fillFromSorted(s);
+ } else if (c instanceof PriorityQueue) {
+ PriorityQueue extends E> s = (PriorityQueue extends E>) c;
+ comparator = (Comparator super E>)s.comparator();
+ fillFromSorted(s);
} else {
- */
- {
comparator = null;
- for (Iterator i = initialElements.iterator(); i.hasNext(); )
- add(i.next());
+ fillFromUnsorted(c);
}
}
+ /**
+ * 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. This priority queue will be sorted
+ * according to the same comparator as the given collection, or
+ * according to its elements' natural order if the collection is
+ * sorted 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
+ */
+ public PriorityQueue(PriorityQueue extends E> c) {
+ initializeArray(c);
+ comparator = (Comparator super E>)c.comparator();
+ fillFromSorted(c);
+ }
+
+ /**
+ * 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. This priority queue will be sorted
+ * according to the same comparator as the given collection, or
+ * according to its elements' natural order if the collection is
+ * sorted 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
+ */
+ public PriorityQueue(SortedSet extends E> c) {
+ initializeArray(c);
+ comparator = (Comparator super E>)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;
+ }
+ Object[] newQueue = new Object[newlen];
+ System.arraycopy(queue, 0, newQueue, 0, queue.length);
+ queue = newQueue;
+ }
+
// Queue Methods
+
+
/**
- * Remove and return the minimal element from this priority queue if
- * it contains one or more elements, otherwise null. The term
- * minimal is defined according to this priority queue's order.
+ * Add the specified element to this priority queue.
*
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
+ * @return true
+ * @throws ClassCastException if the specified element cannot be compared
+ * with elements currently in the priority queue according
+ * to the priority queue's ordering.
+ * @throws NullPointerException if the specified element is null.
*/
+ public boolean offer(E o) {
+ if (o == null)
+ throw new NullPointerException();
+ modCount++;
+ ++size;
+
+ // Grow backing store if necessary
+ if (size >= queue.length)
+ grow(size);
+
+ queue[size] = o;
+ fixUp(size);
+ return true;
+ }
+
public E poll() {
if (size == 0)
return null;
- return remove(1);
+ return (E) remove(1);
}
+ public E peek() {
+ return (E) queue[1];
+ }
+
+ // Collection Methods - the first two override to update docs
+
/**
- * Return, but do not remove, the minimal element from the priority queue,
- * or null if the queue is empty. The term minimal is
- * defined according to this priority queue's order. This method returns
- * the same object reference that would be returned by by the
- * poll method. The two methods differ in that this method
- * does not remove the element from the priority queue.
+ * Adds the specified element to this queue.
+ * @return true (as per the general contract of
+ * Collection.add).
*
- * @return the minimal element from this priority queue if it contains
- * one or more elements, otherwise null.
+ * @throws NullPointerException {@inheritDoc}
+ * @throws ClassCastException if the specified element cannot be compared
+ * with elements currently in the priority queue according
+ * to the priority queue's ordering.
*/
- public E peek() {
- return queue[1];
+ public boolean add(E o) {
+ return super.add(o);
}
- // Collection Methods
-
+
/**
- * Removes a single instance of the specified element from this priority
- * queue, if it is present. Returns true if this collection contained the
- * specified element (or equivalently, if this collection changed as a
+ * Adds all of the elements in the specified collection to this queue.
+ * The behavior of this operation is undefined if
+ * the specified collection is modified while the operation is in
+ * progress. (This implies that the behavior of this call is undefined if
+ * the specified collection is this queue, and this queue is nonempty.)
+ *
+ * This implementation iterates over the specified collection, and adds
+ * each object returned by the iterator to this collection, in turn.
+ * @throws NullPointerException {@inheritDoc}
+ * @throws ClassCastException if any element cannot be compared
+ * with elements currently in the priority queue according
+ * to the priority queue's ordering.
+ */
+ public boolean addAll(Collection extends E> c) {
+ return super.addAll(c);
+ }
+
+
+ /**
+ * Removes a single instance of the specified element from this
+ * queue, if it is present. More formally,
+ * removes an element e such that (o==null ? e==null :
+ * o.equals(e)), if the queue contains one or more such
+ * elements. Returns true if the queue contained the
+ * specified element (or equivalently, if the queue changed as a
* result of the call).
*
- * @param o element to be removed from this collection, if present.
- * @return true if this collection changed as a result of the
- * call
- * @throws ClassCastException if the specified element cannot be compared
- * with elements currently in the priority queue according
- * to the priority queue's ordering.
- * @throws NullPointerException if the specified element is null.
+ *
This implementation iterates over the queue looking for the
+ * specified element. If it finds the element, it removes the element
+ * from the queue using the iterator's remove method.
+ *
*/
- public boolean remove(Object element) {
- if (element == null)
- throw new NullPointerException();
+ public boolean remove(Object o) {
+ if (o == null)
+ return false;
if (comparator == null) {
for (int i = 1; i <= size; i++) {
- if (((Comparable)queue[i]).compareTo(element) == 0) {
+ if (((Comparable)queue[i]).compareTo((E)o) == 0) {
remove(i);
return true;
}
}
} else {
for (int i = 1; i <= size; i++) {
- if (comparator.compare(queue[i], (E) element) == 0) {
+ if (comparator.compare((E)queue[i], (E)o) == 0) {
remove(i);
return true;
}
@@ -214,11 +382,10 @@ public class PriorityQueue extends Ab
}
/**
- * Returns an iterator over the elements in this priority queue. The
- * first element returned by this iterator is the same element that
- * would be returned by a call to peek.
+ * 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 priority queue.
+ * @return an iterator over the elements in this queue.
*/
public Iterator iterator() {
return new Itr();
@@ -229,21 +396,21 @@ public class PriorityQueue extends Ab
* Index (into queue array) of element to be returned by
* subsequent call to next.
*/
- int cursor = 1;
+ 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.
*/
- int lastRet = 0;
+ 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.
*/
- int expectedModCount = modCount;
+ private int expectedModCount = modCount;
public boolean hasNext() {
return cursor <= size;
@@ -253,7 +420,7 @@ public class PriorityQueue extends Ab
checkForComodification();
if (cursor > size)
throw new NoSuchElementException();
- E result = queue[cursor];
+ E result = (E) queue[cursor];
lastRet = cursor++;
return result;
}
@@ -264,8 +431,7 @@ public class PriorityQueue extends Ab
checkForComodification();
PriorityQueue.this.remove(lastRet);
- if (lastRet < cursor)
- cursor--;
+ cursor--;
lastRet = 0;
expectedModCount = modCount;
}
@@ -276,43 +442,11 @@ 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;
}
/**
- * Add the specified element to this priority queue.
- *
- * @param element the element to add.
- * @return true
- * @throws ClassCastException if the specified element cannot be compared
- * with elements currently in the priority queue according
- * to the priority queue's ordering.
- * @throws NullPointerException if the specified element is null.
- */
- public boolean offer(E element) {
- if (element == null)
- throw new NullPointerException();
- modCount++;
-
- // Grow backing store if necessary
- if (++size == queue.length) {
- E[] newQueue = new E[2 * queue.length];
- System.arraycopy(queue, 0, newQueue, 0, size);
- queue = newQueue;
- }
-
- queue[size] = element;
- fixUp(size);
- return true;
- }
-
- /**
* Remove all elements from the priority queue.
*/
public void clear() {
@@ -329,14 +463,12 @@ public class PriorityQueue extends Ab
* Removes and returns the ith element from queue. Recall
* that queue is one-based, so 1 <= i <= size.
*
- * XXX: Could further special-case i==size, but is it worth it?
- * XXX: Could special-case i==0, but is it worth it?
*/
private E remove(int i) {
assert i <= size;
modCount++;
- E result = queue[i];
+ E result = (E) queue[i];
queue[i] = queue[size];
queue[size--] = null; // Drop extra ref to prevent memory leak
if (i <= size)
@@ -357,17 +489,17 @@ public class PriorityQueue extends Ab
if (comparator == null) {
while (k > 1) {
int j = k >> 1;
- if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
+ if (((Comparable)queue[j]).compareTo((E)queue[k]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
} else {
while (k > 1) {
int j = k >> 1;
- if (comparator.compare(queue[j], queue[k]) <= 0)
+ if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
@@ -385,34 +517,79 @@ public class PriorityQueue extends Ab
private void fixDown(int k) {
int j;
if (comparator == null) {
- while ((j = k << 1) <= size) {
- if (j 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(queue[j]) <= 0)
+ if (((Comparable)queue[k]).compareTo((E)queue[j]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
} else {
- while ((j = k << 1) <= size) {
- if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
+ while ((j = k << 1) <= size && j > 0) {
+ if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
j++; // j indexes smallest kid
- if (comparator.compare(queue[k], queue[j]) <= 0)
+ if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
break;
- E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
+ Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
}
+
/**
- * Returns the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
+ * Returns the comparator used to order this collection, or null
+ * if this collection is sorted according to its elements natural ordering
+ * (using Comparable).
*
- * @return the comparator associated with this priority queue, or
- * null if it uses its elements' natural ordering.
+ * @return the comparator used to order this collection, or null
+ * if this collection is sorted according to its elements natural ordering.
*/
- Comparator comparator() {
+ 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
+ * 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=0; iArrayList 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=0; i