You're not being able to use variable 'f' because in inheritance, first base class is initialized and then subclass. I think we can't access derived class variables as they have not yet comes into existence. May be this is the reason that this(f) is giving compilation error.
Member variables gets initialized only after the call to the constructor completes. To be more specific the constructor is intended to construct or initilize the members. [ October 17, 2005: Message edited by: Srinivasa Raghavan ]
In the Java Language Specification Section 18.104.22.168 it states:
An explicit constructor invocation statement in a constructor body may not refer to any instance variables or instance methods declared in this class or any superclass, or use this or super in any expression; otherwise, a compile-time error occurs.
Referring to the original question: The constructor of class Object has not been called before f is referenced in the explicit call to this(f). It is not done until the constructer Test19(float) is executed. So according to the above specification an error must be signalled by the compiler.