What is singleton and Factory Design Pattern?

Singleton – Ensures that at most only one instance of an object exists throughout application. Factory Method – Creates objects of several related classes without specifying the exact object to be created. Abstract Factory – Creates families of related dependent objects.

What is difference between singleton and Factory pattern?

A singleton pattern ensures that you always get back the same instance of whatever type you are retrieving, whereas the factory pattern generally gives you a different instance of each type. The purpose of the singleton is where you want all calls to go through the same instance.

Should a factory be singleton?

The arguments for the factory as a singleton was: Its good to inject everything. Despite the statelessness of the factory, testing is easier with injection (easy to mock) It should be mocked when testing the consumer.

What is a singleton factory pattern with example?

The singleton pattern is one of the simplest design patterns. Sometimes we need to have only one instance of our class for example a single DB connection shared by multiple objects as creating a separate DB connection for every object may be costly.

Why is singleton pattern used?

Singleton pattern restricts the instantiation of a class and ensures that only one instance of the class exists in the java virtual machine. The singleton class must provide a global access point to get the instance of the class.

What is factory pattern used for?

The Factory Method pattern is a design pattern used to define a runtime interface for creating an object. It’s called a factory because it creates various types of objects without necessarily knowing what kind of object it creates or how to create it.

Why use an object factory and how would you implement the Singleton pattern?

Use the Singleton pattern when a class in your program should have just a single instance available to all clients; for example, a single database object shared by different parts of the program. The Singleton pattern disables all other means of creating objects of a class except for the special creation method.

What is difference between singleton and prototype bean?

Singleton: Only one instance will be created for a single bean definition per Spring IoC container and the same object will be shared for each request made for that bean. Prototype: A new instance will be created for a single bean definition every time a request is made for that bean.

Why use an object factory and how would you implement the singleton pattern?

Does factory need to be static?

No, factory class by default shouldn’t be static. Actually, static classes are not welcomed in OOP world since they can also convey some state and therefore introduce global application state. If you need only one factory object to be present, you can control it’s creation through singleton pattern.

Why singleton is used?

It is used where only a single instance of a class is required to control the action throughout the execution. A singleton class shouldn’t have multiple instances in any case and at any cost. Singleton classes are used for logging, driver objects, caching and thread pool, database connections.

What is the purpose of Singleton design pattern?

In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one “single” instance. This is useful when exactly one object is needed to coordinate actions across the system.