• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Jeanne Boyarsky
  • Ron McLeod
  • Paul Clapham
  • Liutauras Vilda
Sheriffs:
  • paul wheaton
  • Rob Spoor
  • Devaka Cooray
Saloon Keepers:
  • Stephan van Hulst
  • Tim Holloway
  • Carey Brown
  • Frits Walraven
  • Tim Moores
Bartenders:
  • Mikalai Zaikin

Collections

 
Ranch Hand
Posts: 82
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Which of the collection classes can contain null items and under what conditions.
Can someone please explain.
Thanks
Mahesh
 
Ranch Hand
Posts: 130
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
All collection collections can have null items. Including sets (but only one allowed). This means others can have more than one.
Maps can have one key as null, and multiple values as null.
I am little bit doubtful. Can anyone confirm me please?
thanks,
Natarajan
 
"The Hood"
Posts: 8521
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Set can have no dups and at most 1 null.
List can have dups and many nulls.
Maps can have no dup keys (but can have dup elements) and SOME maps allow nulls
HashMap allows nulls
TreeMap allow nulls EXCEPT those that use natural ordering.
HashTable does NOT allow nulls.
 
I am displeased. You are no longer allowed to read this tiny ad:
a bit of art, as a gift, that will fit in a stocking
https://gardener-gift.com
reply
    Bookmark Topic Watch Topic
  • New Topic