public class SignUp extends AppCompatActivity{
private EditText txtEmail;
private EditText txtPass;
private FirebaseAuth firebaseAuth;
private DatabaseReference mDatabase;

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

    txtEmail = (EditText) findViewById(R.id.txtEmail);
    txtPass = (EditText) findViewById(R.id.txtPass);
    firebaseAuth = FirebaseAuth.getInstance();
    mDatabase = FirebaseDatabase.getInstance().getReference().child("users");
}
public void SignUp1 (View v) {
    final String email1 = txtEmail.getText().toString();
    String pass1 = txtPass.getText().toString();

    if (!TextUtils.isEmpty(email1) && !TextUtils.isEmpty(pass1)) {
        firebaseAuth.createUserWithEmailAndPassword(email1, pass1).addOnCompleteListener(new OnCompleteListener<AuthResult>()
        {
            public void onComplete(@NonNull Task<AuthResult> task)
            {
                if (task.isSuccessful())
                {
                    String user_id = firebaseAuth.getCurrentUser().getUid();
                    DatabaseReference current_user = mDatabase.child(user_id);
                    current_user.child("Name").setValue(email1);
                    Intent i = new Intent(SignUp.this, SignIn.class);
                    startActivity(i);
                }
            }
        });
    }
}

private EditText txtEmail1;
private EditText txtPass1;
private FirebaseAuth firebaseAuth;
private DatabaseReference mDatabase;


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

    txtEmail1 = (EditText) findViewById(R.id.txtEmail1);
    txtPass1 = (EditText) findViewById(R.id.txtPass1);
    firebaseAuth = FirebaseAuth.getInstance();
    mDatabase = FirebaseDatabase.getInstance().getReference().child("users");


}
public void SignInClicked(View v)
{
    String uname = txtEmail1.getText().toString().trim();
    String pass = txtPass1.getText().toString().trim();

    if (!TextUtils.isEmpty(uname) && !TextUtils.isEmpty(pass))
    {
        firebaseAuth.signInWithEmailAndPassword(uname, pass)
                .addOnCompleteListener(new OnCompleteListener<AuthResult>()
                {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task)
                    {
                        if (task.isSuccessful()) {
                            checkUserExists();
                        }
                    }
                });
    }
}
public void checkUserExists(){
    final String user_id = firebaseAuth.getCurrentUser().getUid();
    mDatabase.addValueEventListener(new ValueEventListener(){@Override
        public void onDataChange(DataSnapshot dataSnapshot)
        {
            if (dataSnapshot.hasChild(user_id))
            {
                Intent i2 = new Intent(SignIn.this, Menu.class);
                startActivity(i2);
            }

        }
        public void onCancelled(DatabaseError databaseError)
        {

        }
    });
}