Enthuware

I knew this is a compile error. In translation phase the corresponding servlet class for the jsp page is compiled. At that time this error is discovers.

But i don't understand why question in enthuware.jwpv6.2.791 is having the answer D.
It is quiet similar to this question. If the compiler can understand the relationships between classes like in this question, it should also can identify the valid constructors of classes.

please explain me. My exam is on tomorrow.

This is OCJP stuff. In 2.791, Beans.instantiate method doesn't know what class it is going to instantiate until runtime. Observe that we are passing the class name as a string argument to Beans.instantiate method. The compiler doesn't evaluate such things. Compilation finds errors only with things that are known at compile time.

It is possible that at time time of writing the JSP page, the class may not even exist. That is the whole point of reflection. Obviously, compiler cannot know whether the class will exist at runtime or not. It can be known only at runtime.