SignInActivity Firebase Auth

import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.RelativeLayout;
import android.widget.TextView;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;

public class SignInActivity extends AppCompatActivity {

  private TextView mBtnSignIn;
  private EditText mEtEmail, mEtPassword;
  private RelativeLayout root, mRlSignUp, mRlFadingLayout;
  private ProgressBar mProgressBar;

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

    mBtnSignIn = findViewById(R.id.txtBtnLogin);
    mEtPassword = findViewById(R.id.etPass);
    mEtEmail = findViewById(R.id.etEmail);
    root = findViewById(R.id.rlSigInRoot);
    mRlSignUp = findViewById(R.id.rlSignUp);
    mRlFadingLayout = findViewById(R.id.rlFadingLayout);
    mProgressBar = findViewById(R.id.progressBar);

    mRlSignUp.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View view) {
        startActivity(new Intent(SignInActivity.this, SignUpActivity.class));
        finish();
      }
    });

    mBtnSignIn.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View view) {
     
        String email = mEtEmail.getText().toString();
        String password = mEtPassword.getText().toString();

        FirebaseAuth firebaseAuth = FirebaseAuth.getInstance();
        firebaseAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(
            new OnCompleteListener<AuthResult>() {
              @Override
              public void onComplete(@NonNull Task<AuthResult> task) {

                mProgressBar.setVisibility(View.INVISIBLE);
                mRlFadingLayout.setVisibility(View.INVISIBLE);

                if (task.isSuccessful()) {
                  startActivity(new Intent(SignInActivity.this, MainActivity.class));
                  finish();
                } else {
                  Snackbar
                      .make(root, task.getException().getLocalizedMessage(), Snackbar.LENGTH_LONG)
                      .show();
                }
              }
            });

      }
    });

  }
}