In Java, nested classes are categorized as either static member classes or inner classes. Inner classes are non-static member classes, local classes, or anonymous classes.

An abstract class can declare fields, constructors, and non-abstract methods in addition to or instead of abstract methods. For example, an abstract Vehicle class might declare fields describing ...

There is a reason why Java method modifiers exist. If you call public methods internally and don't understand why, your developers could face major class issues.