Re: Singletons?
"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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