Trying to create 1 interface and 2 concrete classes inside a Parent class. This will qualify the enclosing classes to be Inner classes.
public class Test2 {
To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:
OuterClass.InnerClass innerObject = outerObject.new InnerClass();
So you need to use :
A a = new Test2().new C();
Refer the Java Tutorial.