Re: Idiom for forcing class loading?

Kevin McMurtrie <>
Wed, 18 Nov 2009 23:05:49 -0800
In article <>,
 Tom Anderson <> wrote:

Hi chaps,

We have a class which does some setup in a static block that needs to
happen early in the lifecycle of the app (this is a dubious design, but
there you go - it's largely forced on us from without). Thus, it needs to
get loaded early. We have an initialiser class which runs at a suitable
time, so that's where we'll load the class. What's the best way to do

Before i came to it, the code looked like:

void initialise() {

I didn't like that, because it's using a string constant where it could be
using something strongly typed, and so not getting enabling refactoring
and inspection in the IDE. I had a bit of a debate with my pair, and we
changed it to:

void initialise() {

Which works, solves the problem, and is clearly bonkers.

What's a good idiom? One option would be to call a no-op method on the
class literal:

void initialise() {

But that's a bit hackish too. I could just store it in a local:

void initialise() {
  Class foo = Foo.class;

Since i actually have several classes, i could put them in an array:

void initialise() {
  Class[] loadedClasses = new Class[] {Foo.class, Bar.class, Baz.class};

Am i right in thinking that all of these will force loading of Foo? Does
anyone have any other idioms? How about any opinions on which idiom is
best, or at least most idiomatic?


You can access a non-optimizable static field or static method. A
constructor for an instance of the class is the safest bet.

Self-registering classes are not the best design. Under extremely rare
circumstances, references from live classes to the registration
container might not exist during a GC - then it's suddenly empty. In a
web server or other application with multiple ClassLoaders, it might not
be clear where things are going. For the work I've done, there were
enough problems to justify not using JDBC driver self-registration with

Consider a configuration parameter that is a list of classes that your
registration container should load when it initializes.
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