What it means is probably that, if a class has no other methods or fields, then you only access it for the singleton, so the singleton is only created when demanded. Otherwise, for example
class Foo
{
public static final Foo foo = new Foo();
public static int x() { return 0; }
}
class AnotherClass
{
void test()
{
print(Foo.x());
}
}
here, foo
was instantiated, though it was never asked for.
But it's ok to have private static methods/fields, so others won't trigger class initialization by accident.