How to Customize the Ordering of Elements in a PriorityQueue Using a Comparator in Java?

A PriorityQueue is a data structure that allows elements to be processed based on their priority. By default, it orders elements according to their natural ordering (e.g., numeric values in ascending order). However, sometimes we need a different sorting order based on specific criteria.

In this article, we will learn to Customize the Ordering of Elements in a PriorityQueue Using a Comparator in Java.

Prerequisites:

• Java Collections Framework
• Comparator vs Comparable.

Customize the Ordering of Elements in a PriorityQueue

Using a Custom Comparator to customize the ordering of elements in a PriorityQueue, follow these steps:

• When constructing a PriorityQueue, provide a custom comparator a define the desired order.
• The constructor PriorityQueue (int capacity, Comparator<E> comparator) allows you to create a PriorityQueue with a specified initial capacity and a custom comparator.
• The comparator determines how elements are compared and ordered.

Program to Customize the Ordering of Elements in a PriorityQueue

Let's create a PriorityQueue of students based on their CGPA (grade point average). We'll define a custom comparator (StudentComparator) that compares students' CGPA values

Below is the implementation of Customize the Ordering of Elements in a PriorityQueue:

Students served in their priority order:
Palak
Anmol
Nandini

Explanation of the above Program:

• In the example above, we create a priorityQueue of Students.
• The custom comparator (StudentComparator) orders students based on their CGPA.
• Students with higher CGPA are served first, demonstrating customized ordering.

Let's explore another approach for customizing the ordering of elements in a PriorityQueue using a Comparator in java.

Ordering Strings by Length

Suppose we want to create a PriorityQueue that orders strings based on their length (number of characters). we'll define a custom comparator to achieve this.Create a new Java file (e.g., StringLengthPriorityQueue.java)

Below is the implementation of Ordering Strings by Length:

Strings served in order of length:
kiwi
apple
grape
banana

Explanation of the above Program:

• In this example, we create a PriorityQueue of Strings.
• The custom comparator ( StringLengthComparator ) compares strings based on their length.
• Strings with shorter lengths are served first.