MainActivity.java

Observable<Integer> observer1 = Observable.from(new Integer[]{1, 2, 3, 4, 5});  //Emit 1 to 5
Observable<Integer> observer2 = Observable.from(new Integer[]{6, 7, 8, 9, 10}); //Emit 6 to 10

Observable.concat(observer1, observer2) //Concat the output of both the operators.
        .subscribeOn(Schedulers.newThread())
        .observeOn(Schedulers.io())
        .subscribe(new Action1<Integer>() {
            @Override
            public void call(Integer integer) {
                Log.d("Observer", "Output:" + integer);
            }
        });