Thread: absX cannot be resolved or its not a field

Hello, maybe someone could explain me (new to coding) what does this error mean and how do i fix that? All of these errors seem to be the same - absX cannot be resolved or its not a field.

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I changed project to Gradle and it seemed to fix the errors but I cant find how to run the server/source. This means that it has no main class or whats the problem then?

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Thanks.