edu.emory.mathcs.backport.java.util.concurrent
Class PriorityBlockingQueue
java.util.AbstractCollection
- BlockingQueue, Collection, Queue, java.io.Serializable
public class PriorityBlockingQueue
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()). 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
../../../../../../../../guide/collections/index.html">
Java Collections Framework.
PriorityBlockingQueue() - Creates a PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their natural ordering.
|
PriorityBlockingQueue(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.
|
PriorityBlockingQueue(int initialCapacity, Comparator comparator) - Creates a PriorityBlockingQueue with the specified initial
capacity that orders its elements according to the specified
comparator.
|
boolean | add(Object e) - Inserts the specified element into this priority queue.
|
void | clear() - Atomically removes all of the elements from this queue.
|
Comparator | comparator() - Returns the comparator used to order the elements in this queue,
or null if this queue uses the natural ordering of its elements.
|
boolean | contains(Object o) - Returns
true if this queue contains the specified element.
|
int | drainTo(Collection c)
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int | drainTo(Collection c, int maxElements)
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Iterator | iterator() - Returns an iterator over the elements in this queue.
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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() - Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
|
Object | poll() - Retrieves and removes the head of this queue,
or returns null if this queue is empty.
|
Object | poll(long timeout, TimeUnit unit)
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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.
|
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.
|
String | toString()
|
PriorityBlockingQueue
public PriorityBlockingQueue()
Creates a PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their natural ordering.
PriorityBlockingQueue
public PriorityBlockingQueue(Collection c)
Creates a
PriorityBlockingQueue containing the elements
in the specified collection. If the specified collection is a
java.util.SortedSet
or a
PriorityQueue
, this
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.
c
- the collection whose elements are to be placed
into this priority queue
PriorityBlockingQueue
public PriorityBlockingQueue(int initialCapacity)
Creates a PriorityBlockingQueue with the specified
initial capacity that orders its elements according to their
natural ordering.
initialCapacity
- the initial capacity for this priority queue
PriorityBlockingQueue
public PriorityBlockingQueue(int initialCapacity,
Comparator comparator)
Creates a PriorityBlockingQueue with the specified initial
capacity that orders its elements according to the specified
comparator.
initialCapacity
- the initial capacity for this priority queuecomparator
- the comparator that will be used to order this
priority queue. If null
, the natural ordering of the elements will be used.
add
public boolean add(Object e)
Inserts the specified element into this priority queue.
- add in interface BlockingQueue
- add in interface Queue
- add in interface AbstractQueue
- true (as specified by
Collection.add
)
clear
public void clear()
Atomically removes all of the elements from this queue.
The queue will be empty after this call returns.
- clear in interface AbstractQueue
comparator
public Comparator comparator()
Returns the comparator used to order the elements in this queue,
or null if this queue uses the natural ordering of its elements.
- the comparator used to order the elements in this queue,
or null if this queue uses the natural
ordering of its elements
contains
public boolean contains(Object o)
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)
.
- contains in interface BlockingQueue
o
- object to be checked for containment in this queue
- true if this queue contains the specified element
iterator
public 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 "weakly consistent"
iterator that will never throw java.util.ConcurrentModificationException
, and guarantees to traverse
elements as they existed upon construction of the iterator, and
may (but is not guaranteed to) reflect any modifications
subsequent to construction.
- an iterator over the elements in this queue
offer
public boolean offer(Object e)
Inserts the specified element into this priority queue.
- offer in interface BlockingQueue
- offer in interface Queue
offer
public boolean offer(Object e,
long timeout,
TimeUnit unit)
Inserts the specified element into this priority queue. As the queue is
unbounded this method will never block.
- offer in interface BlockingQueue
e
- the element to addtimeout
- This parameter is ignored as the method never blocksunit
- This parameter is ignored as the method never blocks
peek
public Object peek()
Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
- peek in interface Queue
- the head of this queue, or null if this queue is empty
poll
public Object poll()
Retrieves and removes the head of this queue,
or returns null if this queue is empty.
- poll in interface Queue
- the head of this queue, or null if this queue is empty
put
public void put(Object e)
Inserts the specified element into this priority queue. As the queue is
unbounded this method will never block.
- put in interface BlockingQueue
remainingCapacity
public int remainingCapacity()
Always returns Integer.MAX_VALUE because
a PriorityBlockingQueue is not capacity constrained.
- remainingCapacity in interface BlockingQueue
remove
public boolean remove(Object o)
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 and only if this queue contained
the specified element (or equivalently, if this queue changed as a
result of the call).
- remove in interface BlockingQueue
o
- element to be removed from this queue, if present
- true if this queue changed as a result of the call
toArray
public Object[] toArray()
Returns an array containing all of the elements in this queue.
The returned array elements are in no particular order.
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.
- toArray in interface AbstractCollection
- an array containing all of the elements in this queue
toArray
public 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.
The returned array elements are in no particular order.
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 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().
- toArray in interface AbstractCollection
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
- an array containing all of the elements in this queue
toString
public String toString()