That means it doesn't know what to do when you say "populate()". Do you have a method written for populate()? example: private void populate() { (what to do....) } I can tell detail more if you want :D! It's an important part of coding.

We'd need to see your code for certain - but the above advice is a common cause! If you have declared a populate() method then check it's the same case (Java is case sensitive) and check your curly brackets are all in the right place which can also sometimes cause that error.