proper usage of synchronized singleton?

Question

So I am thinking about building a hobby project, one off kind of thing, just to brush up on my programming/design.

It\'s basically a multi threaded web spider, upda

Answer 1

Double-checked locking has been proven to be incorrect and flawed (as least in Java). Do a search or look at Wikipedia's entry for the exact reason.

First and foremost is program correctness. If your code is not thread-safe (in a multi-threaded environment) then it's broken. Correctness comes first before performance optimization.

To be correct you'll have to synchronize the whole getInstance method

public static synchronized Singleton getInstance() {
   if (instance==null) ...
}

or statically initialize it

private static final Singleton INSTANCE = new Singleton();