Rewrite:

Rewrite:
- constructors of concrete (=implementing non-abstract) classes should be
  private to avoid somone making an inheriting class of a concrete class
- this is good practice: only make inheriting (concrete) classes of abstract
  classes, not another concrete class only because you want that functionality
  in your class, too
- the private constructor also stops you from doing such wrong things, no need
  to make all concrete classes final

Signed-off-by: Roland Häder <roland@mxchange.org>