vb.net - Classes, references to save memory -

i have class follows:

public class courses     public coursesofferedmain new list(of category)     public courseslist new list(of course)     public semslist new list(of sem)     public subjectslist new list(of subjects)     public examstypelist new list(of examtype)      public class category         private categoryname string         private deleted boolean         public courses new list(of course)     end class     public class course         private categoryname string         private courseid string         private coursename string         private deleted boolean         public sems new list(of sem)      end class     public class sem         private categoryname string         private courseid string         private semid string         private semname string         private deleted boolean         public subjects new list(of subjects)     end class     public class subjects         private categoryname string         private courseid string         private semid string         private subjectid string         private subjectname string         private deleted boolean         public exams new list(of examtype)     end class     public class examtype         private categoryname string         private courseid string         private semid string         private subjectid string         private examtypeid string         private examname string         private exammax string         private exammin string         private exampass string         private deleted boolean     end class      public sub updatelists()         courseslist.clear()         semslist.clear()         subjectslist.clear()         examstypelist.clear()         each cat category in coursesofferedmain             each cour course in cat.courses                 courseslist.add(cour)                 each sems sem in cour.sems                     semslist.add(sems)                     each subj subjects in sems.subjects                         subjectslist.add(subj)                         each exam examtype in subj.exams                             examstypelist.add(exam)                         next                     next                 next             next         next     end sub end class 

there no problem code how ever, know, in process following, number of subjects, couses, examsets etc repeated in specific type lists subjectslist, examstypelist etc.. since being copied on take more memory.

hence, question or doubt be, possible use same references instead of copying them on lists save memory, or there methods better this?

you using references. classes reference types, when copy objects copying references objects.