TheQueue
implementations are grouped into general-purpose and concurrent implementations.General-Purpose Queue Implementations
As mentioned in the previous section,LinkedList
implements theQueue
interface, providing FIFO queue operations foradd
,poll
, and so on.The
PriorityQueue
class is a priority queue based on the heap data structure. This queue orders elements according to an order specified at construction time, which can be the elements' natural ordering or the ordering imposed by an explicitComparator
.The queue retrieval operations
poll
,remove
,peek
, andelement
access the element at the head of the queue. The head of the 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; ties are broken arbitrarily.
PriorityQueue
and its iterator implement all the optional methods of theCollection
andIterator
interfaces. The iterator provided in methoditerator
is not guaranteed to traverse the elements of thePriorityQueue
in any particular order. If you need ordered traversal, consider usingArrays.sort(pq.toArray())
.Concurrent Queue Implementations
Thejava.util.concurrent
package contains a set of synchronizedQueue
interfaces and classes.BlockingQueue
extendsQueue
with operations that wait for the queue to become nonempty when retrieving an element and for space to become available in the queue when storing an element. This interface is implemented by the following classes:
LinkedBlockingQueue
an optionally bounded FIFO blocking queue backed by linked nodesArrayBlockingQueue
a bounded FIFO blocking queue backed by an arrayPriorityBlockingQueue
an unbounded blocking priority queue backed by a heapDelayQueue
a time-based scheduling queue backed by a heapSynchronousQueue
a simple rendezvous mechanism that uses theBlockingQueue
interface