An unbounded priority queue
based on a priority heap. The elements of the priority queue are ordered according to their natural ordering
, or by a
provided at queue construction time, depending on which constructor is used. A priority queue does not permit
elements. A priority queue relying on natural ordering also does not permit insertion of non-comparable objects (doing so may result in
The head of this 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. The queue retrieval operations
element access the element at the head of the queue.
A priority queue is unbounded, but has an internal capacity governing the size of an array used to store the elements on the queue. It is always at least as large as the queue size. As elements are added to a priority queue, its capacity grows automatically. The details of the growth policy are not specified.
This class and its iterator implement all of the optional methods of the
Iterator interfaces. The Iterator provided in method
iterator() and the Spliterator provided in method
spliterator() are not guaranteed to traverse the elements of the priority queue in any particular order. If you need ordered traversal, consider using
Note that this implementation is not synchronized. Multiple threads should not access a
PriorityQueue instance concurrently if any of the threads modifies the queue. Instead, use the thread-safe
Implementation note: this implementation provides O(log(n)) time for the enqueuing and dequeuing methods (
add); linear time for the
contains(Object) methods; and constant time for the retrieval methods (
This class is a member of the Java Collections Framework .