java.util.concurrent.PriorityBlockingQueue<E>
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 implements 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()).
Summary
Public Constructors
Public Methods
add,
addAll,
clear,
contains,
containsAll,
isEmpty,
iterator,
remove,
removeAll,
retainAll,
size,
toArray,
toArray,
toString
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
add,
addAll,
clear,
contains,
containsAll,
equals,
hashCode,
isEmpty,
iterator,
remove,
removeAll,
retainAll,
size,
toArray,
toArray
Methods inherited
from interface
java.util.Queue
Details
Public Constructors
public
PriorityBlockingQueue()
Creates a PriorityBlockingQueue with the default initial
capacity
(11) that orders its elements according to their natural
ordering (using Comparable).
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. |
public
PriorityBlockingQueue(int initialCapacity, Comparator<? super E> 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. |
public
PriorityBlockingQueue(Collection<? extends E> 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
ClassCastException
| if elements of the specified collection
cannot be compared to one another according to the priority
queue's ordering. |
NullPointerException
| if c or any element within it
is null
|
Public Methods
public
boolean
add(E o)
Adds the specified element to this queue.
Returns
- true (as per the general contract of
Collection.add).
Throws
NullPointerException
| if the specified element is null. |
ClassCastException
| if the specified element cannot be compared
with elements currently in the priority queue according
to the priority queue's ordering.
|
public
void
clear()
Atomically removes all of the elements from this delay queue.
The queue will be empty after this call returns.
public
Comparator<? super E>
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.
public
boolean
contains(Object o)
Searches this Collection for the specified object.
Parameters
o
| the object to search for |
Returns
- true if
object
is an element of this Collection,
false otherwise
public
int
drainTo(Collection<? super E> c, int maxElements)
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.
public
int
drainTo(Collection<? super E> c)
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.
public
Iterator<E>
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.
Returns
- an iterator over the elements in this queue.
public
boolean
offer(E o, long timeout, TimeUnit unit)
Inserts the specified element into this priority queue. As the queue is
unbounded this method will never block.
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 |
Throws
ClassCastException
| if the 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.
|
public
boolean
offer(E o)
Inserts the specified element into this priority 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.
|
public
E
peek()
Gets but not removes the element in the head of the queue, or throws
exception if there is no element in the queue.
public
E
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.
public
E
poll()
Gets and removes the element in the head of the queue, or returns null if
there is no element in the queue.
public
void
put(E o)
Adds the specified element to this priority queue. As the queue is
unbounded this method will never block.
Throws
ClassCastException
| if the 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.
|
public
int
remainingCapacity()
Always returns
Integer.MAX_VALUE because
a
PriorityBlockingQueue is not capacity constrained.
public
boolean
remove(Object o)
Removes the first occurrence of the specified object from this
Collection. This operation traverses over the collection, looking
for the specified object. Once the object is found, the object will
be removed from the collection using the iterator's remove method.
This collection will throw an UnsupportedOperationException if the
iterator returned does not implement remove method, and the specified
object is in this collection.
Returns
- true if this Collection is modified, false otherwise
public
int
size()
Returns the number of elements in this Collection.
Returns
- the number of elements in this Collection
public
E
take()
Retrieves and removes the head of this queue, waiting
if no elements are present on this queue.
public
T[]
toArray(T[] a)
Returns an array containing all elements contained in this Collection. If
the specified array is large enough to hold the elements, the specified
array is used, otherwise an array of the same type is created. If the
specified array is used and is larger than this Collection, the array
element following the collection elements is set to null.
Returns
- an array of the elements from this Collection
public
Object[]
toArray()
Returns a new array containing all elements contained in this Collection.
All the elements in the array will not be referenced by the collection.
The elements in the returned array will be sorted to the same order as
those returned by the iterator of this collection itself if the collection
guarantees the order.
Returns
- an array of the elements from this Collection
public
String
toString()
Returns the string representation of this Collection. The presentation
has a specific format. It is enclosed by square brackets ("[]"). Elements
are separated by ', ' (comma and space).
Returns
- the string representation of this Collection