JoinObservable.java

        /*
         * We create two Observables: left & right which emits a value every 100 milliseconds.
         * We join left Observable to the right Observable.
         * The two integers emitted from both the Observables are added
         * & the result is printed.
         *
         * */
        Observable<Long> left = Observable
                .interval(100, TimeUnit.MILLISECONDS);

        Observable<Long> right = Observable
                .interval(100, TimeUnit.MILLISECONDS);

        left.join(right,
                aLong -> Observable.timer(0, TimeUnit.SECONDS),
                aLong -> Observable.timer(0, TimeUnit.SECONDS),
                (l, r) -> {
                    System.out.println("Left result: " + l + " Right Result: " + r);
                    return l + r;
                })
                .subscribe(new Observer<Long>() {
                    @Override
                    public void onSubscribe(Disposable d) {

                    }

                    @Override
                    public void onNext(Long aLong) {
                        System.out.println("onNext: " + aLong);
                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onComplete() {

                    }
                });

        Thread.sleep(1000);