In my opinion, the biggest advantage of array is that we can access to any element with O(1). But a queue can only be accessed from the head or the tail.
Besides, PriorityBlockingQueue is a sorted collection, which means every single add operation will cause all larger(or smaller) elements to shift. That's quite expensive.
So I don't understand why not using a linked list instead.
Besides, PriorityBlockingQueue is a sorted collection, which means every single add operation will cause all larger(or smaller) elements to shift.
You misunderstood the inner workings of the PriorityBlockingQueue: it does not shift up or down the entire array; that would indeed be too expensive. Instead, it uses a data structure called heap, which uses an array for its storage, but does not apply "plain" indexing to it. Instead, it stores items in a tree-like way, making O(log2n) insertions and removals possible.
For details on how PriorityBlockingQueue maintains the heap see implementations of shiftDown and shiftUp in PriorityQueue.java.
Because the underlying data structure is really a binary heap, which is most efficiently implemented via an array, and which in turn provides O(log(N)) performance on addition and removal. An LinkedList could not possibly be as efficient as a heap.
Besides, PriorityBlockingQueue is a sorted collection, which means every single add operation will cause all larger(or smaller) elements to shift.
No it won't. It will cause a re-heapify operation, which is considerably more efficient than what you describe.
PriorityBlockingQueueshould use a similar strategy.