CountDownTimer suing RXJava 2

CountDownTime.java

import java.util.concurrent.TimeUnit;

import io.reactivex.Observer;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.disposables.Disposable;
import io.reactivex.schedulers.Schedulers;

/**
 * Created by Angelo Moroni on 27/04/17.
 */

public abstract class CountDownTimer {

    private TimeUnit timeUnit;
    private Long startValue;
    private Disposable disposable;

    public CountDownTimer(Long startValue,TimeUnit timeUnit) {
        this.timeUnit = timeUnit;
        this.startValue = startValue;
    }

    public abstract void onTick(long tickValue);

    public abstract void onFinish();

    public void start(){
        io.reactivex.Observable.zip(
                io.reactivex.Observable.range(0, startValue.intValue()), io.reactivex.Observable.interval(1, timeUnit), (integer, aLong) -> {
                    Long l = startValue-integer;
                    return l;
                }
        ).subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<Long>() {
                    @Override
                    public void onSubscribe(Disposable d) {
                        disposable = d;
                    }

                    @Override
                    public void onNext(Long aLong) {
                        onTick(aLong);
                    }

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

                    @Override
                    public void onComplete() {
                        onFinish();
                    }
                });
    }

    public void cancel(){
        if(disposable!=null) disposable.dispose();
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.start_activity);

        new CountDownTimer(10L, TimeUnit.SECONDS) {

            @Override
            public void onTick(long tickValue) {
                Log.d("CountDown", "Remaining: " + tickValue);
            }

            @Override
            public void onFinish() {
                Log.d("CountDown", "The End!! ");
            }
        }.start();
    }
}