question: public void register ( Class < ? extends Lang > clazz ) throws Exception { if ( clazz == null ) { throw new NullPointerException ( "argument 'clazz' cannot be null" ) ; } List < String > fileExtensions = getFileExtensionsFromClass ( clazz ) ; for ( int i = fileExtensions . size ( ) ; -- i >= 0 ; ) { String ext = fileExtensions . get ( i ) ; if ( langHandlerRegistry . get ( ext ) == null ) { langHandlerRegistry . put ( ext , clazz ) ; } else { throw new Exception ( "cannot override language handler " + ext ) ; } } }
target:  Register language handler. The clazz will not be instantiated