[RXJAVA] subscribeOn메소드

Question

package com.example.secha.androidnodejs;


import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Toast;

import com.afollestad.materialdialogs.DialogAction;
import com.afollestad.materialdialogs.MaterialDialog;
import com.example.secha.androidnodejs.Retrofit.INodeJS;
import com.example.secha.androidnodejs.Retrofit.RetrofitClient;
import com.github.javiersantos.materialstyleddialogs.MaterialStyledDialog;
import com.google.android.material.button.MaterialButton;
import com.rengwuxian.materialedittext.MaterialEditText;

import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.disposables.CompositeDisposable;
import io.reactivex.functions.Consumer;
import io.reactivex.schedulers.Schedulers;
import retrofit2.Retrofit;



public class MainActivity extends AppCompatActivity {
    INodeJS myAPI;
    final CompositeDisposable compositeDisposable = new CompositeDisposable();

    MaterialEditText edt_email,edt_password;
    MaterialButton btn_register,btn_login;

    @Override
    protected void onStop() {
        compositeDisposable.clear();
        super.onStop();
    }

    @Override
    protected void onDestroy() {
        compositeDisposable.clear();
        super.onDestroy();
    }

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

        //init API
        Retrofit retrofit = RetrofitClient.getInstance();
        myAPI=retrofit.create(INodeJS.class);

        //view
        btn_login=(MaterialButton) findViewById(R.id.login_button);
        btn_register=(MaterialButton) findViewById(R.id.register_button);

        edt_email=(MaterialEditText) findViewById(R.id.edt_email);
        edt_password=(MaterialEditText) findViewById(R.id.edt_password);

        //event
        btn_login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                loginUser(edt_email.getText().toString(),edt_password.getText().toString());
            }
        });

        btn_register.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                registerUser(edt_email.getText().toString(),edt_password.getText().toString());
            }
        });

    }

    private void registerUser(final String email, final String password) {

        final View enter_name_view = LayoutInflater.from(this).inflate(R.layout.enter_name_layout,null);
        new MaterialStyledDialog.Builder(this)
                .setTitle("회원가입")
                .setDescription("one more step")
                .setCustomView(enter_name_view)
                .setIcon(R.drawable.ic_user)
                .setNegativeText("cancel")
                .onNegative(new MaterialDialog.SingleButtonCallback() {
                    @Override
                    public void onClick(@NonNull MaterialDialog dialog, @NonNull DialogAction which) {
                        dialog.dismiss();
                    }
                })
                .setPositiveText("Register")
                .onPositive(new MaterialDialog.SingleButtonCallback() {
                    @Override
                    public void onClick(@NonNull MaterialDialog dialog, @NonNull DialogAction which) {
                        MaterialEditText edt_name = (MaterialEditText)enter_name_view.findViewById(R.id.edt_name);

                        compositeDisposable.add(myAPI.registerUser(email,edt_name.getText().toString(),password)
                        .subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(new Consumer<String>() {
                            @Override
                            public void accept(String s) throws Exception {
                                Toast.makeText(MainActivity.this,""+s,Toast.LENGTH_SHORT).show();

                            }
                        }));

                    }
                }).show();

    }

    private void loginUser(String email, String password) {

        compositeDisposable.add(myAPI.loginUser(email,password)
            .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<String>() {
                    @Override
                    public void accept(String s) throws Exception {
                        if(s.contains("encrypted_password"))
                            Toast.makeText(MainActivity.this,"로그인 성공",Toast.LENGTH_SHORT).show();
                        else
                            Toast.makeText(MainActivity.this,""+s,Toast.LENGTH_SHORT).show();

                    }
                })
        );
    }


}

여기서 subscribeOn 메소드에 빨간줄이 생기고 작동이 안되네요. 이유를 모르겠습니다...