Java Priority Queue — Free Java Tutorial

TL;DR: Learn Java Priority Queue in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Java Priority Queue in Java

PriorityQueue is a min-heap by default — poll() always returns the smallest element. Use Collections.reverseOrder() or a custom Comparator for a max-heap.

Operations: offer(e) (insert), poll() (remove smallest), peek() (view smallest without removing). All are O(log n) except peek which is O(1).

PriorityQueue does not maintain sorted order for iteration — only the head element (accessible via peek/poll) is guaranteed to be the minimum.

Common uses: Dijkstra's shortest path, A* search, task scheduling by priority, merging sorted lists, finding top-K elements.

// Min-heap (default)
PriorityQueue<Integer> minHeap = new PriorityQueue<>();
minHeap.offer(5); minHeap.offer(1); minHeap.offer(3);
minHeap.poll();  // 1 (smallest)

// Max-heap
PriorityQueue<Integer> maxHeap = new PriorityQueue<>(Collections.reverseOrder());

// Custom priority
PriorityQueue<Task> tasks = new PriorityQueue<>(
    Comparator.comparingInt(t -> t.priority));

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