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Java Academy · Lesson

PriorityQueue for Ordered Processing

Use PriorityQueue with natural ordering and custom comparators for task scheduling scenarios.

What is a PriorityQueue?

A PriorityQueue is a min-heap by default: the element with the lowest natural ordering is always at the head. Elements are not sorted internally — only the minimum is guaranteed at the front.

import java.util.PriorityQueue;

PriorityQueue<Integer> pq = new PriorityQueue<>();
pq.offer(30);
pq.offer(10);
pq.offer(20);

System.out.println(pq.poll()); // 10 (min)
System.out.println(pq.poll()); // 20
System.out.println(pq.poll()); // 30

Internal Heap Structure

PriorityQueue uses a binary min-heap stored in an array. The parent at index i is always ≤ its children at 2i+1 and 2i+2. This guarantees O(log n) offer/poll and O(1) peek.

All lessons in this course

  1. LinkedList Internals
  2. Deque Operations: Stack and Queue
  3. LinkedList vs ArrayList Trade-offs
  4. PriorityQueue for Ordered Processing
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