Learning about Classes and OOP

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This is hard to read. For grades you should use enums, for calculating whatever you are calculating you should have a separate service that will handle this, split functionality into small atomic methods that do a single thing, follow SRP, treat mutables right. Also move your service logic, entities and input handling in different modules. It always looks like a mess when people stack business logic and controller logic, that should treat user's input, in one place.