In the
Java Language Specification Section 8.8.7.1 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.