If multiple elements are tied for least value, the head is one of those elements ties are broken arbitrarily. The head of the queue is the least element with respect to the specified ordering. The queue retrieval operations poll, remove, peek, and element access the element at the head of the queue. This queue orders elements according to the order specified at construction time, which can be the elements' natural ordering or the ordering imposed by an explicit Comparator. PriorityQueue class is a priority queue based on the heap data structure. General-Purpose Queue ImplementationsĪs mentioned in the previous section, LinkedList implements the Queue interface, providing first in, first out (FIFO) queue operations for add, poll, and so on. Same runtime type is allocated for this purpose.The Queue implementations are grouped into general-purpose and concurrent implementations. Specified by: toArray in interface Collection Overrides: toArray in class AbstractCollection Parameters: a - the array into which the elements of the queue are toīe stored, if it is big enough otherwise, a new array of the Note that toArray(new Object) is identical in function to The following code can be used to dump the queue into a newly Suppose x is a queue known to contain only strings. Under certain circumstances, be used to save allocation costs. Precise control over the runtime type of the output array, and may, Like the toArray() method, this method acts as bridge betweenĪrray-based and collection-based APIs. The array immediately following the end of the collection is set to (i.e., the array has more elements than the queue), the element in If the queue fits in the specified array with room to spare Specified array and the size of this queue. Otherwise, a new array is allocated with the runtime type of the If the queue fits in the specified array, it is returned therein. The returned array elements are in no particular order. Runtime type of the returned array is that of the specified array. Returns an array containing all of the elements in this queue the Methods and constant time for the retrieval methods Linear time for the remove(Object) and contains(Object) O(log(n)) time for the enqueing and dequeing methods Implementation note: this implementation provides Instead, use the thread-safe PriorityBlockingQueue class. Instance concurrently if any of the threads modifies the queue. Multiple threads should not access a PriorityQueue Note that this implementation is not synchronized. Traversal, consider using Arrays.sort(pq.toArray()). The priority queue in any particular order. The Iterator provided in method iterator() is not guaranteed to traverse the elements of Optional methods of the Collection and Iterator interfaces. This class and its iterator implement all of the As elements are added to a priority queue, its capacity It is always at least as large as the queue The queue retrieval operations poll,Ī priority queue is unbounded, but has an internalĬapacity governing the size of an array used to store theĮlements on the queue. Tied for least value, the head is one of those elements - ties areīroken arbitrarily. The head of this queue is the least element Insertion of non-comparable objects (doing so may result in A priority queue does not permit null elements.Ī priority queue relying on natural ordering also does not permit Provided at queue construction time, depending on which constructor is The elements of the priority queue are ordered according to their An unbounded priority queue based on a priority heap.
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