As always, start with the basics -- your World subclass and Actor classes. Actors should interact or positioned to determine when a user action is to be executed. Depending on what you want, add a timing system or some type of a scoring system, or both (controlled by the world). If you have specific problems with the code, then show codes, indicate how it is not doing what you want and what you do want.

Hey, thanks for the response! Maybe I should've been a bit more specific with my question; I see that now. I have a general idea of how all the main features, timing, scoring, and collisions are going to work, but I am having trouble with the actual charting. I was thinking of just manually spawning new notes as the song went on, but that would be a little bit troublesome to get the timing and offset exactly right. I've looked into analyzing the audio for the chart separately, in an audio editor, and using the timestamps from that to use in Greenfoot to more accurately spawn the notes in time, but I don't know if that's the best course of action. So, is there a way I could create a file that holds the data for the chart outside of Greenfoot, and be able to import it into my project for use somehow? Or do you perhaps have any ideas of what would be the best way to create the chart?

Hiya! Looks like Danpost here is calling you a noob, but don't worry, I know way better than to call you a noob. You are a complex mastermind at Greenfoot and could demolish Danpost at any given time. I'm reaching my trembling hands out to you with extreme caution because I sure don't want to get on your bad side! Just to clarify, you don't need to be any more specific in your question, it was perfect in every single aspect; it was Danpost's incapability to understand your question and acknowledge that your game needs RHYTHM not some "basic" code. Lucky for you, I'm a retired Salsa and cupid shuffle dancer who is willing to teach you the rhythm, but only under one condition.... Danpost must shuffle "to the right, to the right," out of this discussion. This is between only YOU and ME. "Now kick, now kick" Danpost out of this chat with me, and he can walk through this code by himself. Now back to teaching you rhythm, you can come over anytime, and I'll always have chips and salsa out because eating salsa makes you better at salsa dancing, and I would know because I've only had chips and salsa with a side of salsa for the past 30 years (P.S.- I'm 30 years old...Hah time flies by so fast). I remember when I was a little baby, drinking the salsa out from my baby bottle. In fact, before I had milk, I had a spoon of Salsa first. People say when I was younger I was so obsessed with salsa that my used diapers would be 100% decomposed and digested salsa. Don't ask about my son by the way because we aren't on speaking terms...he did the unacceptable (He had Guacamole instead of Salsa). I know your game is a Rhythm game so if you need an Actor that will be dancing with full rhythm that makes Salsa itself jealous, I'm here. I'm known for making people's spine shiver as they see me hit my moves. Just a quick warning, 3 people's spines have snapped while watching me, due to the intense shivering, so the preformance may be interuppted by a strange bone cracking noise. So be sure to include a waiver for your game before anyone accesses it if you're willing to put me in it, which I'm 99.99% sure you will, just as hand sanitizers promise my hands will be clean, which my hands always are. So anyways, I'm expecting a full response from you INCLUDING a thanks just like how my buddy Danpost received. The best dancer, and yours truly, xoxo, (To the right~) Philip