title: final fields and thread-safety
body: <p>Should it be all fields, including super-fields, of a purposely immutable java class 'final' in order to be thread-safe or is it enough to have no modifier methods?</p>
  <p>Suppose I have a POJO with non-final fields where all fields are type of some immutable class. This POJO has getters-setters, and a constructor which sets some initial value. If I extend this POJO with knocking out modifier methods, thus making it immutable, will extension class be thread-safe?</p>