in auth/src/main/java/com/google/firebase/quickstart/AuthSnippets.java [29:35]
public static void getUserById(String uid) throws InterruptedException, ExecutionException {
// [START get_user_by_id]
UserRecord userRecord = FirebaseAuth.getInstance().getUserAsync(uid).get();
// See the UserRecord reference doc for the contents of userRecord.
System.out.println("Successfully fetched user data: " + userRecord.getUid());
// [END get_user_by_id]
}