question: private static void initializeRegistry ( ) { register ( PipelineOptions . class ) ; Set < PipelineOptionsRegistrar > pipelineOptionsRegistrars = Sets . newTreeSet ( ObjectsClassComparator . INSTANCE ) ; pipelineOptionsRegistrars . addAll ( Lists . newArrayList ( ServiceLoader . load ( PipelineOptionsRegistrar . class , CLASS_LOADER ) ) ) ; for ( PipelineOptionsRegistrar registrar : pipelineOptionsRegistrars ) { for ( Class < ? extends PipelineOptions > klass : registrar . getPipelineOptions ( ) ) { register ( klass ) ; } } }
target:  Load and register the list of all classes that extend PipelineOptions.