Priority queue ordering of elements

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Actually internal data structure of PriorityQueue is not ordered, it is a heap.

PriorityQueue doesn’t need to be ordered, instead, it focuses on head of data. Insertion is in O(log n) time. Sorting wastes time and useless for a queue.

Moreover, either the element is-a Comparable, or a Comparator is provided. Unfortunately, non-comparable checking is at runtime, rather than compile time. Once second element is added, ClassCastException occurs.

PLUS: My answer to why [1, 3, 2, 4] instead of prints [1, 2, 3, 4]?

As I mentioned before, it’s not ordered, instead it focuses on head q[0] is minimum, that’s it.
You could see the [1, 3, 2, 4] as a tree which is NOT linear:

1
| \
3  2
|
4

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