edu.emory.mathcs.util.concurrent
Class PriorityBlockingQueue

java.lang.Object
  |
  +--java.util.AbstractCollection
        |
        +--edu.emory.mathcs.util.AbstractQueue
              |
              +--edu.emory.mathcs.util.concurrent.PriorityBlockingQueue
All Implemented Interfaces:
BlockingQueue, java.util.Collection, Queue, java.io.Serializable

public class PriorityBlockingQueue
extends AbstractQueue
implements BlockingQueue, java.io.Serializable

An unbounded blocking queue that uses the same ordering rules as class PriorityQueue and supplies blocking retrieval operations. While this queue is logically unbounded, attempted additions may fail due to resource exhaustion (causing OutOfMemoryError). This class does not permit null elements. A priority queue relying on natural ordering also does not permit insertion of non-comparable objects (doing so results in ClassCastException).

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()).

This class is a member of the Java Collections Framework.

Since:
1.5
See Also:
Serialized Form

Constructor Summary
PriorityBlockingQueue()
          Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering (using Comparable).
PriorityBlockingQueue(java.util.Collection c)
          Creates a PriorityBlockingQueue containing the elements in the specified collection.
PriorityBlockingQueue(int initialCapacity)
          Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering (using Comparable).
PriorityBlockingQueue(int initialCapacity, java.util.Comparator comparator)
          Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.
 
Method Summary
 boolean add(java.lang.Object o)
          Adds the specified element to this queue.
 void clear()
          Atomically removes all of the elements from this queue.
 java.util.Comparator comparator()
          Returns the comparator used to order this collection, or null if this collection is sorted according to its elements natural ordering (using Comparable).
 boolean contains(java.lang.Object o)
           
 int drainTo(java.util.Collection c)
          Removes all available elements from this queue and adds them into the given collection.
 int drainTo(java.util.Collection c, int maxElements)
          Removes at most the given number of available elements from this queue and adds them into the given collection.
 java.util.Iterator iterator()
          Returns an iterator over the elements in this queue.
 boolean offer(java.lang.Object o)
          Inserts the specified element into this priority queue.
 boolean offer(java.lang.Object o, long timeout, TimeUnit unit)
          Inserts the specified element into this priority queue.
 java.lang.Object peek()
          Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.
 java.lang.Object poll()
          Retrieves and removes the head of this queue, or null if this queue is empty.
 java.lang.Object poll(long timeout, TimeUnit unit)
          Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.
 void put(java.lang.Object o)
          Adds the specified element to this priority queue.
 int remainingCapacity()
          Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.
 boolean remove(java.lang.Object o)
          Removes a single instance of the specified element from this queue, if it is present.
 int size()
           
 java.lang.Object take()
          Retrieves and removes the head of this queue, waiting if no elements are present on this queue.
 java.lang.Object[] toArray()
           
 java.lang.Object[] toArray(java.lang.Object[] a)
           
 java.lang.String toString()
           
 
Methods inherited from class edu.emory.mathcs.util.AbstractQueue
addAll, element, remove
 
Methods inherited from class java.util.AbstractCollection
containsAll, isEmpty, removeAll, retainAll
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface edu.emory.mathcs.util.Queue
element, remove
 
Methods inherited from interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, removeAll, retainAll
 

Constructor Detail

PriorityBlockingQueue

public PriorityBlockingQueue()
Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering (using Comparable).


PriorityBlockingQueue

public PriorityBlockingQueue(int initialCapacity)
Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering (using Comparable).

Parameters:
initialCapacity - the initial capacity for this priority queue.
Throws:
java.lang.IllegalArgumentException - if initialCapacity is less than 1

PriorityBlockingQueue

public PriorityBlockingQueue(int initialCapacity,
                             java.util.Comparator comparator)
Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.

Parameters:
initialCapacity - the initial capacity for this priority queue.
comparator - the comparator used to order this priority queue. If null then the order depends on the elements' natural ordering.
Throws:
java.lang.IllegalArgumentException - if initialCapacity is less than 1

PriorityBlockingQueue

public PriorityBlockingQueue(java.util.Collection c)
Creates a PriorityBlockingQueue 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 is a SortedSet or a PriorityQueue, this 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, this priority queue is ordered according to its elements' natural order.

Parameters:
c - the collection whose elements are to be placed into this priority queue.
Throws:
java.lang.ClassCastException - if elements of the specified collection cannot be compared to one another according to the priority queue's ordering.
java.lang.NullPointerException - if c or any element within it is null
Method Detail

add

public boolean add(java.lang.Object o)
Adds the specified element to this queue.

Specified by:
add in interface BlockingQueue
Overrides:
add in class AbstractQueue
Parameters:
o - the element to add
Returns:
true (as per the general contract of Collection.add).
Throws:
java.lang.NullPointerException - if the specified element is null.
java.lang.ClassCastException - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.

comparator

public java.util.Comparator comparator()
Returns the comparator used to order this collection, or null if this collection is sorted according to its elements natural ordering (using Comparable).

Returns:
the comparator used to order this collection, or null if this collection is sorted according to its elements natural ordering.

offer

public boolean offer(java.lang.Object o)
Inserts the specified element into this priority queue.

Specified by:
offer in interface BlockingQueue
Parameters:
o - the element to add
Returns:
true
Throws:
java.lang.ClassCastException - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.
java.lang.NullPointerException - if the specified element is null.

put

public void put(java.lang.Object o)
Adds the specified element to this priority queue. As the queue is unbounded this method will never block.

Specified by:
put in interface BlockingQueue
Parameters:
o - the element to add
Throws:
java.lang.ClassCastException - if the element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.
java.lang.NullPointerException - if the specified element is null.

offer

public boolean offer(java.lang.Object o,
                     long timeout,
                     TimeUnit unit)
Inserts the specified element into this priority queue. As the queue is unbounded this method will never block.

Specified by:
offer in interface BlockingQueue
Parameters:
o - 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:
java.lang.ClassCastException - if the element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.
java.lang.NullPointerException - if the specified element is null.

take

public java.lang.Object take()
                      throws java.lang.InterruptedException
Description copied from interface: BlockingQueue
Retrieves and removes the head of this queue, waiting if no elements are present on this queue.

Specified by:
take in interface BlockingQueue
Returns:
the head of this queue
Throws:
java.lang.InterruptedException - if interrupted while waiting.

poll

public java.lang.Object poll()
Description copied from interface: Queue
Retrieves and removes the head of this queue, or null if this queue is empty.

Specified by:
poll in interface Queue
Returns:
the head of this queue, or null if this queue is empty.

poll

public java.lang.Object poll(long timeout,
                             TimeUnit unit)
                      throws java.lang.InterruptedException
Description copied from interface: BlockingQueue
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.

Specified by:
poll in interface BlockingQueue
Parameters:
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameter
Returns:
the head of this queue, or null if the specified waiting time elapses before an element is present.
Throws:
java.lang.InterruptedException - if interrupted while waiting.

peek

public java.lang.Object peek()
Description copied from interface: Queue
Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.

Specified by:
peek in interface Queue
Returns:
the head of this queue, or null if this queue is empty.

size

public int size()
Specified by:
size in interface java.util.Collection
Specified by:
size in class java.util.AbstractCollection

remainingCapacity

public int remainingCapacity()
Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.

Specified by:
remainingCapacity in interface BlockingQueue
Returns:
Integer.MAX_VALUE

remove

public boolean remove(java.lang.Object o)
Removes a single instance of the specified element from this queue, if it is present.

Specified by:
remove in interface java.util.Collection
Overrides:
remove in class java.util.AbstractCollection

contains

public boolean contains(java.lang.Object o)
Specified by:
contains in interface java.util.Collection
Overrides:
contains in class java.util.AbstractCollection

toArray

public java.lang.Object[] toArray()
Specified by:
toArray in interface java.util.Collection
Overrides:
toArray in class java.util.AbstractCollection

toString

public java.lang.String toString()
Overrides:
toString in class java.util.AbstractCollection

drainTo

public int drainTo(java.util.Collection c)
Description copied from interface: BlockingQueue
Removes all available elements from this queue and adds them into the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:
drainTo in interface BlockingQueue
Parameters:
c - the collection to transfer elements into
Returns:
the number of elements transferred.

drainTo

public int drainTo(java.util.Collection c,
                   int maxElements)
Description copied from interface: BlockingQueue
Removes at most the given number of available elements from this queue and adds them into the given collection. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:
drainTo in interface BlockingQueue
Parameters:
c - the collection to transfer elements into
maxElements - the maximum number of elements to transfer
Returns:
the number of elements transferred.

clear

public void clear()
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.

Specified by:
clear in interface java.util.Collection
Overrides:
clear in class AbstractQueue

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)
Specified by:
toArray in interface java.util.Collection
Overrides:
toArray in class java.util.AbstractCollection

iterator

public java.util.Iterator iterator()
Returns an iterator over the elements in this queue. The iterator does not return the elements in any particular order. The returned iterator is a thread-safe "fast-fail" iterator that will throw ConcurrentModificationException upon detected interference.

Specified by:
iterator in interface java.util.Collection
Specified by:
iterator in class java.util.AbstractCollection
Returns:
an iterator over the elements in this queue.