Why does adding a public field to an anonymous class in Java not work?

Question

I have an example class defined like below:

public class FooBar {

  void method1(Foo foo){ // Should be overwritten
    ...
  }

}

Later,

Answer 1

You're creating an object of type foobar. The compiler only knows about the members defined for the class/interface foobar.

Remember, java is a static language, not dynamic. It doesn't check the object at runtime for what exists, it checks at compile time based on the type declaration.