Simple factory factory method Abstract Factory

Simple factory ： Factories can create the same series of products , The interface of the product is consistent , But the factory must judge which product to create according to the parameters （ Simple factories have no subclasses , Generally speaking, create instances directly in the factory through enumeration ）.

such as ： The noodle shop has onion noodles , Beef noodles , egg noodle ... What kind of noodles would you like , It depends on your taste .

Factory method ： There can be a variety of factories , Factories have common interfaces , A factory can produce only one product , Compared with a simple factory , The factory method does not require judgment , Reduced coupling （ Define the interface for creating objects , Instantiation is the responsibility of subclasses , And only one kind can be instantiated ）

such as ： Boss Yang has three stores ： Those who only sell steamed buns Steamed bun shop , Water that only sells water , Coffee only The coffee shop

Abstract factory ： Can produce multiple series of products （ involves The concept of product family ： In different product grades , A family of products with related functions ）（ Define the interface for creating objects , Define all products , Instantiation is the responsibility of subclasses , Whether a product can be created depends entirely on it ）

such as ： McDonald's boss ： Coke system products , Hamburger series products , There are three kinds of products, large, medium and small

The biggest difference between simple factory and factory method is ： Factory methods do not make logical judgments in factory classes , The system can provide different factories for different product categories , Different factories produce different products .（ The factory method is convenient for adding new products ）

The biggest difference between factory method and abstract factory is ： Abstract factories create objects that are more complex , The intention of abstract factory is ： Provide an interface , You can create product objects in multiple product families , such as NSNumber Medium NSCFNumber and NSCFBoolean.（ Because the creation of products is determined by abstract classes , So it is inconvenient to add new products ）