Why “t instanceof T” is not allowed where T is a type parameter and t is a variable?

Question

Eclipse says that the instanceof operation is not allowed with Type Parameter due to generic type eraser.

I agree that at runtime, no type information stays. But con

Answer 1

But if I instantiate this class of type Integer, then the corresponding object will have a field t of type Integer.

Actually, it wouldn't. It'd have a field t of type Object. As you've said, generics are almost entirely syntactic sugar (the exception is that when you extend a generic class and specify a type parameter, the type remains as metadata in the class file).