Pattern: Stateless singleton
Issue: -
There is no point in creating a stateless Singleton because there is nothing within the class that needs guarding and no side effects to calling the constructor. Just create new instances of the object or write a Utility class with static methods. In the long term, Singletons can cause strong coupling and hard to change systems.
If the class has any fields at all, other than a self reference, then it is not considered stateless. A self reference is a field of the same type as the enclosing type, or a field named instance or _instance.
Example of violations:
@groovy.lang.Singleton
class Service {
// violation: the class has no fields but is marked Singleton
void processItem(item){
}
}
class Service {
// violation: the class has no fields other than 'instance' but is marked Singleton
static instance
void processItem(item){
}
}
class Service { // violation
static Service service
void processItem(item){
}
}