functional interface in java 8 example

1package com.concretepage;
2
3@FunctionalInterface
4public interface Calculator {
5   long calculate(long num1, long num2);
6} 

1@FunctionalInterface
2interface Square
3{
4    int calculate(int x);
5}
6  
7class Test
8{
9    public static void main(String args[])
10    {
11        int a = 5;
12  
13        // lambda expression to define the calculate method
14        Square s = (int x)->x*x;
15  
16        // parameter passed and return type must be
17        // same as defined in the prototype
18        int ans = s.calculate(a);
19        System.out.println(ans);
20    }
21}