SingleFeatures.java

package rx.single;

import org.junit.Test;
import rx.Observable;
import rx.Single;
import rx.schedulers.Schedulers;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;


/**
 * @author Pablo Perez
 *         Single is just another variant of observable as relay. In this particular case Single only emit one item.
 *         Since only emit 1 item in the pipeline, single  only accept two Action functions, onSuccess and onError.
 */
public class SingleFeatures {


    /**
     * Here we can see constantClass basic example where Single just emit the item and onSuccess and onError functions are defined.
     */
    @Test
    public void testSingle() {
        Single.just("Single").subscribe(result -> System.out.println("Result: " + result),
                (error) -> System.out.println("Something went wrong" + error.getMessage()));
    }


    /**
     * The fact that Single only emit 1 item does not means that cannot use all the ReactiveX features as zip, merge, concat, and so on.
     * Here we use Zip to run two singles, which every one of those it will emit just 1 item.
     */
    @Test
    public void testZipSingles() {
        Single<Integer> single = Single.just(1);
        Single<Integer> single2 = Single.just(2);
        Single.zip(single, single2, (s1, s2) -> s1 + s2)
                .subscribe(result -> System.out.println("Result: " + result),
                        (error) -> System.out.println("Something went wrong" + error.getMessage()));
    }

    /**
     * Also it´ possible use Single asynchronously using subscribeOn or observerOn
     */
    @Test
    public void testSinglesAsync() {
        System.out.println("Current thread:" + Thread.currentThread()
                .getName());
        Single.just("Single").subscribeOn(Schedulers.newThread())
                .subscribe(result -> System.out.println("Async Result in thread: " + Thread.currentThread()
                                .getName()),
                        (error) -> System.out.println("Something went wrong" + error.getMessage()));
    }

    /**
     * flatMapObservable operator merge all items from constantClass list from Single into n observable of the list type
     */
    @Test
    public void flatMapObservable() {
        Observable.just(Collections.singletonList(1))
                .flatMap(word -> getObservables()
                        .flatMapObservable(Observable::from))
                .collect(ArrayList<String>::new, List::add)
                .subscribe(System.out::println, System.out::println, System.out::println);

    }

    private Single<List<String>> getObservables() {
        return Single.just(Arrays.<String>asList("Hello", " flatMapObservable", " operator"));
    }

}