Generic Comparator in Java

Introduction

When working with Java, Sorting is an essential operation that every developer needs to understand. Thankfully, Java provides robust tools and interfaces to make this task easier. One such tool is the Comparator interface. 

This article will explore how we can create a generic Comparator to compare objects of a user-defined class in Java.

The Basics of Comparator

The Comparator interface in Java is used for sorting collections of objects. It allows you to order objects based on user-defined conditions, adding a level of customization to the sorting process. A typical Comparator interface might look like this:

Comparator<T> {
    int compare(T o1, T o2);
}

The compare method takes two objects for comparison and returns an integer. If the return value is negative, o1 is less than o2. If it's zero, both are equal. If it's positive, o1 is greater than o2.

Creating a User-Defined Class

Let's create a user-defined class Student which we'll later sort using our generic comparator.

public class Student {
    private String name;
    private int age;


    // constructor, getters and setters
}

Crafting a Generic Comparator

A generic comparator is a flexible tool that allows sorting by different attributes of a user-defined class. Let's create a generic comparator StudentComparator for our Student class.

public class StudentComparator implements Comparator<Student> {
    @Override
    public int compare(Student s1, Student s2) {
        return s1.getName().compareTo(s2.getName());
    }
}

Here, the StudentComparator compares Student objects based on their names. You can change this comparison criterion according to your requirements.

Sorting with Comparator

Now that we have a comparator, we can use it to sort a list of students:

List<Student> students = // initialization
Collections.sort(students, new StudentComparator());

The above line will sort the students list based on the students' names in alphabetical order.

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