Re: Subclass of Singleton

From:

"Oliver Wong" <owong@castortech.com>

Newsgroups:

comp.lang.java.help

Date:

Mon, 20 Nov 2006 13:18:07 -0500

Message-ID:

<Djm8h.77823$L27.774577@wagner.videotron.net>

"Andy" <andysm@gmx.de> wrote in message news:ejsi0a$ofl$1@news.sap-ag.de...

Udhaya schrieb:

Hi,

     In some web site when i was looking about Static vs Singleton
difference i found the following

    terms.

   "Creation of several subclasses of the original Singleton class"

   Is it possible to create a subclass for Singleton Class
     Regards

uuk

Maybe try something like this:

abstract class A
{
  protected A singleton=null;

  public abstract A getInstance();

}

class B extends A
{
  private B()
  {
  }

  public A getInstance()
  {
    if (singleton==null)
         singleton=new B();

    return singleton;
  }
}

class C extends A
{

  private C()
  {
  }

  public A getInstance()
  {
     if (singleton==null)
           singleton=new C();

     return singleton;
  }
}

I think for this to be a singleton, the getInstance method needs to be
static, in which case you could not override it via inheritance.

- Oliver