Get Firebase Current User and Uid in Android Studio

 

FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
    // User is signed in
    Toast.makeText(this, user.getUid(), Toast.LENGTH_SHORT).show();
} else {
    // No user is signed in
    startActivity(new Intent(ProductActivity.this, OtpSendActivity.class));
    finish();
}