Max-Heap PriorityQueue to keep the k highest items and return them in descending order
If what you want is to keep the top $k$ items at all times what you need is a min-heap, not a max-heap. After every insert you should check if the length is longer than $k$, and if yes, pop.
If you use numbers as your priorities you can turn a max-heap into a min-heap by simply negating the priority.