Can the singleton class be subclassed?
Subclassing a Singleton class may be tricky, since a subclass object cannot be created unless the superclass object has not yet been created. You may want to extend the Singleton class to allow not just a single instance, but some small fixed maximum number of instances.
When should I make a class Singleton?
As per my thoughts, we should make a class as Singleton when we share the same object state across the application. In that case we want the user to to restrict from creating a new instance every time so that they could not maintain the multiple states.
What is the best way to subclass Singleton?
I would argue the most common way to implement a singleton is to use an enum with one instance. That might be a “better” way but definitely not the most common way. In all the projects I have worked on, Singletons are implemented as I have shown above.
Why can’t a Singleton be subclassed?
They deviate from the Single Responsibility Principle. A singleton class has the responsibility to create an instance of itself along with other business responsibilities. However, this issue can be solved by delegating the creation part to a factory object. Singleton classes cannot be sub classed.
Can we extend a Singleton class in Java?
While both can extend other class(es), only Singletons should be able implement or be derived from interfaces. A static class should only allow static methods while Singletons are not bound to use static methods (though in implementation, they should return at least one static method).
How can you create singleton class?
To create the singleton class, we need to have static member of class, private constructor and static factory method.
- Static member: It gets memory only once because of static, itcontains the instance of the Singleton class.
- Private constructor: It will prevent to instantiate the Singleton class from outside the class.