in auth/src/main/java/com/google/firebase/quickstart/AuthSnippets.java [70:80]
public static void createUserWithUid() throws InterruptedException, ExecutionException {
// [START create_user_with_uid]
CreateRequest request = new CreateRequest()
.setUid("some-uid")
.setEmail("user@example.com")
.setPhoneNumber("+11234567890");
UserRecord userRecord = FirebaseAuth.getInstance().createUserAsync(request).get();
System.out.println("Successfully created new user: " + userRecord.getUid());
// [END create_user_with_uid]
}