Whats wrong in the code snippet below ?

[lifeisgreat20009]

(This is not a trick question, there is a potential real problem in using this code)

class Singleton{
         public static Singleton Instance() {
                  if (_instance == null)
                       _instance = new Singleton();
                  return _instance;
         }
         protected Singleton() {}
         private static Singleton _instance = null;
}

[JosAH]

Multiple Threads, each trying to obtain your 'singleton'. Synchronize that static method.

kind regards,

Jos

[dmjpro]

(This is not a trick question, there is a potential real problem in using this code)

class Singleton{
         public static Singleton Instance() {
                  if (_instance == null)
                       _instance = new Singleton();
                  return _instance;
         }
         protected Singleton() {}
         private static Singleton _instance = null;
}

Actually no syntactical error with your code. Then how did you say that it's error?

[JosAH]

Actually no syntactical error with your code. Then how did you say that it's error?

It helps if you read the entire thread first before you hit the 'Submit Reply' button.

kind regards,

Jos

[dmjpro]

@Joash
Sorry!! :(

If i write the code like this...

public SingleTone{
private static _instance = new SingleTone();
public static getInstance(){
return _instance;
}
}

Then should i synchronize it?

[r035198x]

Why not find an article about the Singleton and read it?

[JosAH]

@Joash
Sorry!! :(

If i write the code like this...

public SingleTone{
private static _instance = new SingleTone();
public static getInstance(){
return _instance;
}
}

Then should i synchronize it?

Think: a class is only loaded once by a classloader.

kind regards,

Jos

ps. btw it's 'Singleton', not 'SingleTone'.

[N002213F]

further to Jos' idea of synchronising the static method, the constructor should be private so that noone instantiates it except itself.

http://java.sun.com/developer/technicalArticles/Programming/singletons/