• 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

Doubt with a singleton class

 
Ranch Hand
Posts: 2234
Eclipse IDE Firefox Browser Redhat
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hi please let me know

Is it mantadatory to have a singleton class as a protected / private constructor ??
 
Sheriff
Posts: 22783
131
Eclipse IDE Spring VI Editor Chrome Java Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Ask yourself this question: what classes can call a non-private constructor, and therefore create objects of a class?
 
Ravi Kiran Va
Ranch Hand
Posts: 2234
Eclipse IDE Firefox Browser Redhat
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Thanks Rob , i agree my question is itself is vague .

I go with
For a singleton class, the constructor is made private and
a private static instance variable of its type and a public static method to get access for instatiating the class.


, but sometimes i saw examples where the author keeps the constructor as protected.
so the reason i posted.

can anybody please tell me why this so .
 
Ranch Hand
Posts: 81
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
I see no reason for a singleton class to have a protected constructor. The purpose of "singleton" is then defeated.
 
Ravi Kiran Va
Ranch Hand
Posts: 2234
Eclipse IDE Firefox Browser Redhat
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Thanks sunil . If thats the answer i have no confusion with singletons.
 
Ranch Hand
Posts: 2874
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Sometimes we don't necessarily make the constructor private for testing purposes. I hope you get my point.

Moreover, you might want to read on the exact thing you encountered. Here is the wikipedia entry for Singleton, you need to scroll down a bit till "The solution of Bill Pugh".
 
Ravi Kiran Va
Ranch Hand
Posts: 2234
Eclipse IDE Firefox Browser Redhat
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
thanks a lot
 
Rob Spoor
Sheriff
Posts: 22783
131
Eclipse IDE Spring VI Editor Chrome Java Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Sunil Kumar wrote:I see no reason for a singleton class to have a protected constructor. The purpose of "singleton" is then defeated.


It's mostly done so the singleton class can be subclassed, but I agree that it's a bad idea. Any class in the same package, as well as all sub classes, can also create new instances.
 
Adeel Ansari
Ranch Hand
Posts: 2874
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Singleton Vs JustCreateOne, a must read.
 
reply
    Bookmark Topic Watch Topic
  • New Topic