Java Singleton vs static - is there a real performance benefit?

Question

I am merging a CVS branch and one of the larger changes is the replacement wherever it occurs of a Singleton pattern with abstract classes that have a static initialisation bloc

Answer 1

Static is bad for extensibility since static methods and fields cannot be extended or overridden by subclasses.

It's also bad for unit tests. Within a unit test you cannot keep the side effects of different tests from spilling over since you cannot control the classloader. Static fields initialized in one unit test will be visible in another, or worse, running tests concurrently will yield unpredictable results.

Singleton is generally an ok pattern when used sparingly. I prefer to use a DI framework and let that manage my instances for me (possibly within different scopes, as in Guice).