edu.emory.mathcs.backport.java.util.concurrent
public class PriorityBlockingQueue extends AbstractQueue implements BlockingQueue, Serializable
This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces. The Iterator provided in method iterator is not guaranteed to traverse the elements of the PriorityBlockingQueue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()). Also, method drainTo can be used to remove some or all elements in priority order and place them in another collection.
Operations on this class make no guarantees about the ordering of elements with equal priority. If you need to enforce an ordering, you can define custom classes or comparators that use a secondary key to break ties in primary priority values. For example, here is a class that applies first-in-first-out tie-breaking to comparable elements. To use it, you would insert a new FIFOEntry(anEntry) instead of a plain entry object.
class FIFOEntry implements Comparable { final static AtomicLong seq = new AtomicLong(); final long seqNum; final Object entry; public FIFOEntry(Object entry) { seqNum = seq.getAndIncrement(); this.entry = entry; } public Object getEntry() { return entry; } public int compareTo(FIFOEntr other) { int res = entry.compareTo(other.entry); if (res == 0 && other.entry != this.entry) res = (seqNum < other.seqNum ? -1 : 1); return res; } }
This class is a member of the Java Collections Framework.
Since: 1.5
Constructor Summary | |
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PriorityBlockingQueue()
Creates a PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their Comparable natural ordering. | |
PriorityBlockingQueue(int initialCapacity)
Creates a PriorityBlockingQueue with the specified
initial capacity that orders its elements according to their
Comparable natural ordering.
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PriorityBlockingQueue(int initialCapacity, Comparator comparator)
Creates a PriorityBlockingQueue with the specified initial
capacity that orders its elements according to the specified
comparator.
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PriorityBlockingQueue(Collection c)
Creates a PriorityBlockingQueue containing the elements
in the specified collection. |
Method Summary | |
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boolean | add(Object e)
Inserts the specified element into this priority queue.
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void | clear()
Atomically removes all of the elements from this queue.
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Comparator | comparator()
Returns the comparator used to order the elements in this queue,
or null if this queue uses the Comparable
natural ordering of its elements.
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boolean | contains(Object o)
Returns {@code true} if this queue contains the specified element.
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int | drainTo(Collection c) |
int | drainTo(Collection c, int maxElements) |
Iterator | iterator()
Returns an iterator over the elements in this queue. |
boolean | offer(Object e)
Inserts the specified element into this priority queue.
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boolean | offer(Object e, long timeout, TimeUnit unit)
Inserts the specified element into this priority queue. |
Object | peek() |
Object | poll() |
Object | poll(long timeout, TimeUnit unit) |
void | put(Object e)
Inserts the specified element into this priority queue. |
int | remainingCapacity()
Always returns Integer.MAX_VALUE because
a PriorityBlockingQueue is not capacity constrained. |
boolean | remove(Object o)
Removes a single instance of the specified element from this queue,
if it is present. |
int | size() |
Object | take() |
Object[] | toArray()
Returns an array containing all of the elements in this queue.
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Object[] | toArray(Object[] a)
Returns an array containing all of the elements in this queue; the
runtime type of the returned array is that of the specified array.
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String | toString() |
Parameters: initialCapacity the initial capacity for this priority queue
Throws: IllegalArgumentException if initialCapacity is less than 1
Parameters: initialCapacity the initial capacity for this priority queue comparator the comparator that will be used to order this priority queue. If {@code null}, the Comparable natural ordering of the elements will be used.
Throws: IllegalArgumentException if initialCapacity is less than 1
Parameters: 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 NullPointerException if the specified collection or any of its elements are null
Parameters: e the element to add
Returns: true (as specified by Collection#add)
Throws: ClassCastException if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering NullPointerException if the specified element is null
Returns: the comparator used to order the elements in this queue, or null if this queue uses the natural ordering of its elements
Parameters: o object to be checked for containment in this queue
Returns: true if this queue contains the specified element
Throws: UnsupportedOperationException {@inheritDoc } ClassCastException {@inheritDoc } NullPointerException {@inheritDoc } IllegalArgumentException {@inheritDoc }
Throws: UnsupportedOperationException {@inheritDoc } ClassCastException {@inheritDoc } NullPointerException {@inheritDoc } IllegalArgumentException {@inheritDoc }
Returns: an iterator over the elements in this queue
Parameters: e the element to add
Returns: true (as specified by Queue)
Throws: ClassCastException if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering NullPointerException if the specified element is null
Parameters: e the element to add timeout This parameter is ignored as the method never blocks unit This parameter is ignored as the method never blocks
Returns: true
Throws: ClassCastException if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering NullPointerException if the specified element is null
Parameters: e the element to add
Throws: ClassCastException if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering NullPointerException if the specified element is null
Returns: Integer.MAX_VALUE
Parameters: o element to be removed from this queue, if present
Returns: true if this queue changed as a result of the call
The returned array will be "safe" in that no references to it are 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.
Returns: an array containing all of the elements in this queue
If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set to null.
Like the 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().
Parameters: 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
Returns: 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 NullPointerException if the specified array is null