Rx.java

Observable<String> database = Observable      //Observable. This will emit the data
                .just(new String[]{"1", "2", "3", "4"});    //Operator

 Observer<String> observer = new Observer<String>() {
           @Override
            public void onCompleted() {
                //...
            }

            @Override
            public void onError(Throwable e) {
                //...
            }

            @Override
            public void onNext(String s) {
                //...
            }
        };

database.subscribeOn(Schedulers.newThread())          //Observable runs on new background thread.
        .observeOn(AndroidSchedulers.mainThread())    //Observer will run on main UI thread.
        .subscribe(observer);                         //Subscribe the observer