How to implement thread-safe lazy initialization?

Question

What are some recommended approaches to achieving thread-safe lazy initialization? For instance,

// Not thread-safe
public Foo getI         


        

Answer 1

Put the code in a synchronized block with some suitable lock. There are some other highly specialist techniques, but I'd suggest avoiding those unless absolutely necessary.

Also you've used SHOUTY case, which tends to indicate a static but an instance method. If it is really static, I suggest you make sure it isn't in any way mutable. If it's just an expensive to create static immutable, then class loading is lazy anyway. You may want to move it to a different (possibly nested) class to delay creation to the absolute last possible moment.