Creating a simple modular application

You should be wondering what this modularity is all about, and how to create a modular application in Java. In this recipe, we will try to clear up the confusion around creating modular applications in Java by walking you through a simple example. Our goal is to show you how to create a modular application; hence, we picked a simple example so as to focus on our goal. 

Our example is a simple advanced calculator, which checks whether a number is prime, calculates the sum of prime numbers, checks whether a number is even, and calculates the sum of even and odd numbers.