ProfileActivity.java

import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class ProfileActivity extends AppCompatActivity {

    TextView mName;
    TextView mEmail;

    FirebaseDatabase mDatabase;
    DatabaseReference mUser;
    FirebaseAuth mAuth;

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

        mDatabase = FirebaseDatabase.getInstance();
        mUser = mDatabase.getReference("user");
        mAuth = FirebaseAuth.getInstance();

        mName = findViewById(R.id.fullname);
        mEmail = findViewById(R.id.email);
    }

    @Override
    protected void onStart() {
        super.onStart();
        String userId;
        userId = mAuth.getUid();

        mUser.child(userId).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                Log.d("Snashot: ", dataSnapshot.toString());
                User user = dataSnapshot.getValue(User.class);
                String name = user.name;
                String email = user.email;

                mName.setText("Full Name: " + name);
                mEmail.setText("Email: " + email);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }
}