The built-in iterator for java's PriorityQueue does not traverse the data structure in any particular order. Why?

Question

This is straight from the Java Docs:

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces.

Answer 1

Well, as the Javadoc says, that's how it's been implemented. The priority queue probably uses a binary heap as the underlying data structure. When you remove items, the heap is reordered to preserve the heap property.

Secondly, it's unwise to tie in a specific implementation (forcing a sorted order). With the current implementation, you are free to traverse it in any order and use any implementation.