How to create singletons?

[aidndev]

We need to create singleton classes to cache database data. Using an EJB container we are not guaranteed that truly one object is being instantiated and shared. I have heard various answers to this, including some mysterious "well, it depends on the classloader..." answers. From what I have found online, the answer appears to have something to do with declaring the class final, or using @service, but I don't know if these are definitely the solution. How can we make a singleton that is definitely really a singleton?

[alrubinger]

@Service is a JBoss-specific extension to EJB that will create a Singleton MBean with lifecycle callbacks defined in an @Management interface.

http://trailblazer.demo.jboss.com/EJB3Trail/serviceobjects/jmx/index.html

S,
ALR

[yilmaz_]

final guarantees the singleton but you cant change anything after an instance created.

[alrubinger]

"yilmaz_" wrote:
final guarantees the singleton but you cant change anything after an instance created.

Declaring a class as "final" means that it cannot be subclassed (be the parent to another class). This does not place restrictions on how many instances of the class there may be.

S,
ALR