contoh cara pake retrofit dan interface

private RestServiceInterface restServiceInterface;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_features_login_login);


        restServiceInterface = RestServiceClass.getClient().create(RestServiceInterface.class);

    }

/**
     * Attempts to sign in or register the account specified by the login form.
     * If there are form errors (invalid email, missing fields, etc.), the
     * errors are presented and no actual login attempt is made.
     */
    public void attemptLogin(String email, String password) {
        if(!isEmailValid(email)) {
            new SweetAlertDialog(LoginActivity.this, SweetAlertDialog.ERROR_TYPE)
                    .setTitleText("Error")
                    .setContentText(getResources().getString(R.string.error_invalid_email)).show();
        } else if(!isPasswordValid(password)) {
            new SweetAlertDialog(LoginActivity.this, SweetAlertDialog.ERROR_TYPE)
                    .setTitleText("Error")
                    .setContentText(getResources().getString(R.string.error_invalid_password)).show();
        } else {
            pDialog.show();
            if(RestServiceClass.isNetworkAvailable(LoginActivity.this)){
                login(email, password);
            }else{
                pDialog.dismiss();
                new SweetAlertDialog(LoginActivity.this, SweetAlertDialog.ERROR_TYPE)
                        .setTitleText("Error")
                        .setContentText(getResources().getString(R.string.pastikan_internet_label)).show();
            }
        }
    }

private void login(String email, String password) {

        Call<LoginUser> call1 = restServiceInterface.userLogin(email,password);
        call1.enqueue(new Callback<LoginUser>() {
            @Override
            public void onResponse(Call<LoginUser> call, Response<LoginUser> response) {
                LoginUser result = response.body();
                if(result != null){
                    if(result.getStatus().equals("success")){
                        SharedPreferences.Editor editor = sharedPreferences.edit();
                        editor.putString(getString(R.string.PREFS_TOKEN), result.getData().getToken());
                        editor.putString(getString(R.string.PREFS_USER_ID), result.getData().getUser().get_id());
                        editor.putString(getString(R.string.PREFS_PROFILE), new Gson().toJson(result));

                        //editor.putString("prefs_user_role", "");
                        editor.putString(getString(R.string.PREFS_IS_LOGIN), "1");
                        editor.commit();

                        pDialog.dismiss();
                        startActivity(new Intent(LoginActivity.this, MainActivity.class));
                        ActivityCompat.finishAffinity(LoginActivity.this);

                    }else if(result.getStatus().equals("error")){
                        pDialog.dismiss();
                        new SweetAlertDialog(LoginActivity.this, SweetAlertDialog.ERROR_TYPE)
                                .setTitleText("Error")
                                .setContentText(result.getMessage()).show();
                    }
                } else {
                    pDialog.dismiss();
                    new SweetAlertDialog(LoginActivity.this, SweetAlertDialog.ERROR_TYPE)
                            .setTitleText("Error")
                            .setContentText(result.getMessage()).show();
                }
            }

            @Override
            public void onFailure(Call<LoginUser> call, Throwable t) {
                pDialog.dismiss();
                new SweetAlertDialog(LoginActivity.this, SweetAlertDialog.ERROR_TYPE)
                        .setTitleText("Error")
                        .setContentText(getResources().getString(R.string.error_jaringan)).show();
                call.cancel();
            }
        });
    }