How to Create a PriorityQueue with a Custom Comparator Without Specifying Initial Capacity?

How can I create a Java PriorityQueue using a custom comparator without specifying an initial capacity?

import java.util.PriorityQueue;
import java.util.Comparator;

public class CustomPriorityQueue {
    public static void main(String[] args) {
        // Creating a PriorityQueue with a custom comparator
        PriorityQueue<Integer> pq = new PriorityQueue<>(new Comparator<Integer>() {
            @Override
            public int compare(Integer a, Integer b) {
                return b - a; // Reverse order, larger elements have higher priority
            }
        });

        // Adding elements to the PriorityQueue
        pq.offer(10);
        pq.offer(20);
        pq.offer(5);

        // Polling elements from the PriorityQueue
        while (!pq.isEmpty()) {
            System.out.println(pq.poll()); // Outputs elements in descending order
        }
    }
}

In Java, a PriorityQueue is a specialized queue that orders its elements according to a specified comparator. If you want to initialize a PriorityQueue with a custom comparator and do not wish to specify an initial capacity, you can do so easily without any additional configuration or constraints of default sizing.

PriorityQueue<Type> pq = new PriorityQueue<>(new Comparator<Type>() {
    public int compare(Type a, Type b) {
        // Custom comparison logic here
    }
});

Causes

• Need for priority order in collection elements.
• Desire to use a custom comparison logic for element ordering.

Solutions

• Use the default constructor of PriorityQueue, which allows dynamic resizing based on elements added.
• Pass a custom comparator while creating the PriorityQueue to dictate the order of elements.

Mistake: Forgetting to implement the compare method correctly in the comparator.

Solution: Ensure the compare method returns negative, zero, or positive according to the desired ordering.

Mistake: Assuming the PriorityQueue will always perform optimally when using large datasets without proper testing.

Solution: Monitor performance and consider specifying an initial capacity if many elements will be added.