This is a simple gist to show the minimal requirements to create a lambda in Java 8+

Example.java

/**
 * Lambdas require a Functional Interface and
 * a target method
 *
 */
public class Example {
    public static void main(String[] args) {
        Summation summation = (a, b) -> a + b;
        System.out.println(summation.sum(3, 4));
    }
}

@FunctionalInterface
interface Summation {
    // target method
    int sum(int n, int m);
}