Java PriorityQueue is a specialized queue implementation in the Java programming language that differs from standard queues by ordering its elements according to their natural ordering or according to a Comparator provided at queue construction time. Unlike a standard queue, which operates on a First In First Out (FIFO) principle, a PriorityQueue orders its elements based on their priority, ensuring that the element with the highest priority is always at the front of the queue.
Key Characteristics of Java PriorityQueue
Ordering: Elements in a PriorityQueue are ordered either by their natural ordering (if they implement the Comparable interface) or by a Comparator provided at the time of queue construction. This ordering determines which element is considered the highest priority[1][2][4][5][6][7][8][9][10][11][12][13][14][15].
Element Retrieval: The head of the PriorityQueue, or the 'peek' of the queue, is the element with the highest priority according to the specified ordering. When elements are removed from the queue, they are removed from the head, starting with the highest priority element[1][2][4][5][6][7][8][9][10][11][12][13][14][15].
Internal Data Structure: The PriorityQueue is typically implemented using a heap data structure, which allows for efficient insertion and removal of elements. The most common form of heap used is a binary heap[1][2][4][5][6][7][8][9][10][11][12][13][14][15].
Performance: The operations of adding and removing elements from a PriorityQueue generally have logarithmic time complexity, i.e., $$O(\log n)$$, due to the properties of the heap structure[1][2][4][5][6][7][8][9][10][11][12][13][14][15].
Null Elements: Java's PriorityQueue does not permit null elements. Attempting to add null to a PriorityQueue will throw a NullPointerException[1][2][4][5][6][7][8][9][10][11][12][13][14][15].
