public class BaseApi {
    private static BaseApi instance = null;
    public static CryptoApi service;
    private static OkHttpClient client;
    private static Retrofit retrofit;


        public BaseApi() {
            HttpLoggingInterceptor logger = new HttpLoggingInterceptor();
            logger.setLevel(HttpLoggingInterceptor.Level.BODY);
            client = new OkHttpClient.Builder()
                    .connectTimeout(60, TimeUnit.SECONDS)
                    .readTimeout(30, TimeUnit.SECONDS)
                    .addInterceptor(logger)
                    .build();

            retrofit = new Retrofit.Builder()
                    .baseUrl(BuildConfig.BASE_URL)
                    .client(client)
                    .addConverterFactory(GsonConverterFactory.create())
                    .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                    .build();

            service = retrofit.create(CryptoApi.class);
        }

        public static BaseApi getInstance() {
            if (instance == null) {
                instance = new BaseApi();
            }
            return instance;
        }
    }

public interface CryptoApi {

        @GET("?limit=5")
        Observable<List<Crypto>> getCrypto();

    }

private void getCrypto() {
        Subscription subscription = BaseApi.getInstance().service.getCrypto()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(crypto -> {
                   Log.d("Crypto", crypto.toString())
                }, throwable -> {
                    Log.e("User from server error", String.valueOf(throwable));
                });
        addSubscription(subscription);
    }