What is a Java Comparator and can you provide an example?

What is a Java Comparator and can you provide an example?

A Java Comparator is an interface used to define a custom order for objects. It allows you to compare two objects and determine their order. Here's a simple example:

import java.util.*;

class Person {
    String name;
    int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

class AgeComparator implements Comparator<Person> {
    public int compare(Person p1, Person p2) {
        return Integer.compare(p1.age, p2.age);
    }
}

public class Main {
    public static void main(String[] args) {
        List<Person> people = new ArrayList<>();
        people.add(new Person("Alice", 30));
        people.add(new Person("Bob", 25));
        people.add(new Person("Charlie", 35));

        Collections.sort(people, new AgeComparator());

        for (Person p : people) {
            System.out.println(p.name + " - " + p.age);
        }
    }
}

How does the Comparator interface differ from Comparable?

The Comparator interface is used to define multiple ways to compare objects, while Comparable is used to define a natural ordering for a class. With Comparable, you implement the compareTo method in the class itself, whereas with Comparator, you create a separate class that implements the compare method.

Can you explain how to sort a list using a Comparator?

Sure! To sort a list using a Comparator, you can use the Collections.sort() method and pass the list along with an instance of your Comparator. For example, in the previous code, we sorted a list of Person objects by age using the AgeComparator.

What are some common use cases for Comparators?

Common use cases for Comparators include sorting collections of objects in different ways, such as by name, age, or any other attribute. They are also useful when you need to sort objects that do not have a natural ordering.