RxJava Functions and high order functions (RxJava8)

RxJava8Example.java

package com.company;

import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;

public class Main {

    public static void main(String[] args) {
        //Reactive manifesto 1) event driven 2) scalable 3) reselient 4) responsive
        //  FunctionAsFirstClassCitizens();//function used as variables, instance variables

        //  FunctionPassedAsParameters();

        //  HighOrderFunction(); a function that returns another function 

    }

    private static void HighOrderFunction() {
        Supplier<String> myFunc = CreateCombineAndTransform("Hello"," World",(s)-> s.toUpperCase());

        System.out.println(myFunc.get());
    }

    private static Supplier<String> CreateCombineAndTransform(
            final String a,
            final String b,
            final Function<String, String> transformer) {


        return () -> {

            String result = null;
            if (transformer != null) {
                result = transformer.apply(a) + transformer.apply(b);
            }
            return result;
        };

    }

    private static void FunctionPassedAsParameters() {
        System.out.println(concatAndTransform("Hello", " World",
                (s) -> {
                    return s.toUpperCase();
                }));

        Function<String, String> functionToLower = (s) -> {
            return s.toLowerCase();
        };

        System.out.println(concatAndTransform("Hello", " World", functionToLower));
    }

    private static void FunctionAsFirstClassCitizens() {
        BiFunction<String, String, String> concatFunction = (s, s2) -> {
            return s + s2;
        };

        System.out.println(concatFunction.apply("Hello", " World!"));

        concatFunction = Main::concatString;

        System.out.println(concatFunction.apply("What", " Is Going On"));

        Main main = new Main();
        concatFunction = main::concatString2;

        System.out.println(concatFunction.apply("Why", " God"));
    }

    private static String concatString(String a, String b) {
        return a + b;
    }

    String concatString2(String s, String b) {
        return s + b;
    }

    private static String concatAndTransform(String a, String b, Function<String, String> stringTrasnform) {
        if (stringTrasnform != null) {
            a = stringTrasnform.apply(a);
            b = stringTrasnform.apply(b);

        }
        return a + b;
    }

}