how to set username in firebase auth code example

Example 1: how to check the current user in firebase android

@Override
public void onStart() {
    super.onStart();
    FirebaseUser currentUser = mAuth.getCurrentUser();
    if (currentUser == null) {
        // No user is signed in
    } else {
        // User logged in
    }
}

Example 2: firebase auth update current user

var user = firebase.auth().currentUser;user.updateProfile({  displayName: "Jane Q. User",  photoURL: "https://example.com/jane-q-user/profile.jpg"}).then(function() {  // Update successful.}).catch(function(error) {  // An error happened.});