As far as I understand every bundle in osgi has its own classloader. Let's suppose we have three bundles:1,2,3. There is singleton class in bundle 1. Bundle 2 loads singleton and makes some changes in it. And as far as I understand, if bundle 3 loads singleton too its version of singleton is different. So Singleton in bundle 2 != singleton in bundle 3.
Are my statements right? If they are right, so it is not singleton, is it?
It is true that each bundle has its own classloader, but the classloaders are "shared", depending on the Manifest import-package declaration. Each bundle classloader maintain a private mapping table that tells it which classloader is responsible for providing classes from a particular package.
In your case, when bundle 2 loads the singleton, it does not load the Singleton by itself, it asks the bundle 1 classloader for the class.
