Code sample for an article about Business Logic and Configuration Logic - https://medium.com/@joshiraez/make-your-business-logic-readable-and-your-configuration-logic-extendable-ea151d478423

Main.java

import java.util.function.UnaryOperator;

public class Main {

    //Top level layer
    public static void main(String[] args) {

        sayHi(SHOUTING, "joshi");
        sayGoodbye(AFABLE, "readers");
    }

    //Intermediate layer. This interfaces our main with the core logic.
    private static void sayHi(final Mood howTo, final String otherPerson) {

        sayItOutLoud(
                moody(howTo)
                .apply(
                        greet(otherPerson)
                ));
    }

    private static void sayGoodbye(final Mood howTo, final String otherPerson) {

        sayItOutLoud(
                moody(howTo)
                        .apply(
                                partFrom(otherPerson)
                        ));
    }

    //One layer below. We have three distinct cores:

    //What to talk
    private static String partFrom(final String otherPerson) {
        return "Bye bye "+otherPerson+"!";
    }

    private static String greet(final String otherPerson) {
        return "Hi "+otherPerson+"!";
    }

    //How to output it.
    private static void sayItOutLoud(final String greetings) {
        System.out.println(greetings);
    }

    //And how to tell it. Notice this is the business logic of even another layer
    private static UnaryOperator<String> moody(final Mood howTo){
        return SHOUTING.equals(howTo)
                ? Main::shouting
                : Main::calmly;
    }

    //Yep, THIS ONE which tells us HOW to do it.
    private static String calmly(final String greetings) {
        return greetings.toLowerCase();
    }

    private static String shouting(final String greetings) {
        return greetings.toUpperCase();
    }


    //And finally THERE IS ANOTHER LAYER AT THE BOTTOM, FOR TYPE CONFIGURATION! (Which is the core of the language)

    //Please dont put constants in the end of the file. Just showing layers.
    private static final Mood SHOUTING = Mood.SHOUTING;
    private static final Mood AFABLE = Mood.AFABLE;

    private enum Mood {
        AFABLE,
        SHOUTING
    }
}