Question

I have a web app where I load components lazily. There is a lot of

static Bla bla;
...    
if(bla == null) 
    bla = new Bla();

spread throughout the code. What do I need to do to make sure this is thread safe? Should I just wrap anytime I do one of these initializations in a synchronized block? Is there any problem with doing that?

Answer 1

The best solution for lazy loading on a static field, as described in Effective Java [2nd edition, Item 71, p. 283] and Java Concurrency in Practice [p. 348], is the Initialization on demand holder idiom:

public class Something {
    private Something() {
    }

    private static class LazyHolder {
        private static final Something something = new Something();
    }

    public static Something getInstance() {
        return LazyHolder.something;
    }
}