Double checked locking Article

Question

I was reading this article about \"Double-Checked locking\" and out of the main topic of the article I was wondering why at some point of the article the author uses the nex

Answer 1

For Java 5 and better there is actually a doublechecked variant that can be better than synchronizing the whole accessor. This is also mentioned in the Double-Checked Locking Declaration :

class Foo {
    private volatile Helper helper = null;
    public Helper getHelper() {
        if (helper == null) {
            synchronized(this) {
                if (helper == null)
                    helper = new Helper();
            }
        }
        return helper;
    }
}

The key difference here is the use of volatile in the variable declaration - otherwise it does not work, and it does not work in Java 1.4 or less, anyway.