Re: Singletons?

From:
"Oliver Wong" <owong@castortech.com>
Newsgroups:
comp.lang.java.help
Date:
Tue, 13 Jun 2006 20:05:58 GMT
Message-ID:
<GUEjg.36085$771.18379@edtnps89>
"Ian Shef" <invalid@avoiding.spam> wrote in message
news:Xns97E18456570CFvaj4088ianshef@138.126.254.210...

"Oliver Wong" <owong@castortech.com> wrote in
news:sBEjg.36081$771.3184@edtnps89:

<snip>

FWIW, here's how I
usually implement Singleton in Java:

public class Variant1 {
  private static Variant1 soleInstance = null;

  private Variant1() {
    /*You should declare all your constructors private, to avoid
instantiation. If you don't have any constructors, then create an empty,
zero argument, private constructor like this one.*/
  }

  public static Variant1 getSoleInstance() {
    if (soleInstance == null) {
      soleInstance = new Variant1();
    }
    return soleInstance;
  }


Are you operating in a single thread environment only?


    Yes. [*]

 Where is your
synchronization? Two threads can call getSoleInstance concurrently, and
end up with different instances of Variant1. See
http://java.sun.com/developer/technicalArticles/Programming/singletons/


    Perhaps I should make it a habit to consider concurrency issues more
often...

    - Oliver

[*] Discounting the garbage collector thread, and other threads that
automagically appear but which don't make calls into my code.

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