I am not sure I understand your question fully. The majority of code used in games is not code that the programmer found elsewhere and copied into their program. Most code is written by the programmer themselves, and is completely original. Additionally, the Greenfoot Class documentation, as well as the Java Library documentation does not contain code, but contains codumentation of Classes, which are different types of objects you can use in your program. With that in mind, you say you are looking for 'code', but what are you looking for specifically? A way to move an object? A way to rotate an object? Asking us where to find code is one of the most general questions that can be asked.

^What Builderboy2005 said. If there's something in particular that you're trying to code and are finding it hard to do, then just post the specific problem and we can help you out

I think he might be wondering about how to create original methods? That would make sense, since he said he's tried looking in the API, which consists of methods. Sorry I can't tell you anything about it right now, I'm literally 10 seconds away from going to sleep.

The Greenfoot and Java APIs contain methods that can be used in your code. The code itself is the basic Java language; and how you put your java language statements together is the artform that creates the code. The methods found in the Greenfoot and Java APIs are there because those methods (or groups of methods) are commonly used and you do not have to re-write them to apply them in your code. Yes, the Java API documentation is quite extensive and can be very confusing, but there are also tutorials (trails) you can follow to acquire a better insight on how much of it can be used. Check out the java tutorials.