Java Functional

package asd;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.BinaryOperator;
import java.util.function.Function;

//FunctionalInterface
interface Math{
    public int add(int x, int y);
}
interface Sort{
    public int reversed(String x, String y);
}
public class Main {
    public Main() {
        List<String> names = new ArrayList<>();
        names.add("Clavianus Juneardo");
        names.add("Vincent Colin");
        names.add("Gregory James");
        names.add("Jonathan Ramlie");
        names.add("Billy Purnama");

        // Functional Interface
        Math math = (int x, int y) -> x + y;
        System.out.println(math.add(2, 2));
        Sort sort = (String x, String y) -> y.compareTo(x);
        Collections.reverse(names);

        //Lambda Expression
        Function<Integer, Integer> pow = x -> x*x;
        System.out.println(pow.apply(2));

        BinaryOperator<Integer> add = (x,y) -> x + y;
        System.out.println(add.apply(2,2));

        //parallel function
        names.stream()
            .sorted( (x,y) -> sort.reversed(y,x) )
            .filter( name -> !name.equals("Clavianus Juneardo") )
            .forEach( System.out::println );
    }

    public static void main(String[] args) { new Main(); }
}