code: @Override
      public int compare(U u1, U u2) {
  
          return Double.compare(u2.getLength(), u1.getLength()); // descending
  
      }
docs: /*[deutsch]
  <p>Vergleicht Zeiteinheiten absteigend nach ihrer L&auml;nge. </p>
  
  @param   u1  first time unit
  @param   u2  second time unit
  @return  negative, zero or positive if u1 is greater, equal to
  or smaller than u2