A couple of fine points I'll throw in....
1) to place a class in a package you use the package statement
(package Experimentation.java
2) to use a class from a package use the import statement
(import Experimentation.java
I bring these up because your souce looks as though you just put a line that says
Experimentation.java
as if that were going to put your class in that package.
Next,
3) there is one package statment allowed in a source file. That means that any classes you type in will all go to the same package as specified in the package statement.
That means that it will take at least two separate source files to
test what you are wanting to test.
One will start with
package Experimentation.java;
// code to declare your first class
The other, which will test for access.. will start with
package Extension.java;
import package.java;
// code to declare your second class that tests for access.
NOW you will have two classes in tow different packages....