question: private static HashMap < String , Field > buildFieldCache ( Class < ? > cls ) { final HashMap < String , Field > cache = new HashMap < > ( ) ; final List < Field > fields = getAllFields ( cls ) ; for ( Field fld : fields ) { String name = null ; final Reference refAnn = fld . getAnnotation ( Reference . class ) ; if ( refAnn != null ) name = selectColumnName ( refAnn , fld ) ; if ( name == null ) { final Column colAnn = fld . getAnnotation ( Column . class ) ; if ( colAnn != null ) name = selectColumnName ( colAnn , fld ) ; } if ( name == null ) continue ; cache . put ( name , fld ) ; } return cache ; }
target:  Avoids the need to loop over fields for every column by caching them ahead of time.