What are comparators in Java collections?

What are comparators in Java collections?

Comparators in Java are used to define a custom order for objects in collections. They allow you to sort objects based on specific criteria.

Can you show me an example of how to implement a comparator?

Sure! 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 = Arrays.asList(new Person("Alice", 30), new Person("Bob", 25));
        Collections.sort(people, new AgeComparator());
        // Now people is sorted by age
    }
}

What if I want to sort by multiple fields?

You can chain comparators using thenComparing(). For example, first sort by age, then by name:

Collections.sort(people, Comparator.comparingInt(Person::getAge).thenComparing(Person::getName));