Lambda.java

public class Lambda { // requires >= java 1.8

    interface IntegerMath {
        int operation(int a, int b);

        default IntegerMath swap() {
          return (a, b) -> operation(b, a);
        }
    }

    public static void main(String[] args) {
        IntegerMath addition = (a, b) -> a + b;
        System.out.println(addition.operation(40, 2));

    }
}