Concat-first

package ass.excercises.cvi8.demo1;

import io.reactivex.Observable;

public class ConcatFirst {

    public static void main(String[] args) {
        Observable.just("a", "b")
        .flatMap(item ->
            Observable.concat(
                    Observable.just(item + "1"),
                    Observable.just(item + "2")     // this is never called
            )
            .first("N/A")   // here you can return implementation of IResponse that represents some kind of error
            .toObservable()
        )
        .forEach(System.out::println);

        System.out.println("=====");

        Observable.just("c", "d")
        .flatMap(item ->
            Observable.concat(
                    Observable.empty(),         // simulates cache that didn't return anything
                    Observable.just(item + "2") // now it's called
            )
            .first("N/A")
            .toObservable()
        )
        .forEach(System.out::println);
    }
}