Factory mode

As a mode of creating objects , Where complex objects need to be generated , Can use factory mode  

Complex objects are suitable for factory mode , And simple objects , In particular, only through new You can complete the created object , No need to use factory mode . If you use factory mode , You need to introduce a factory class , It will increase the complexity of the system

advantage ：

Can make the code structure clear , Effectively encapsulate changes , Good scalability

Block specific product categories from callers （ Dimitar's law ）

Reduce coupling

Simple factory model ：

Factory , Abstract product , Specific products

The concrete commodity is realized by inheriting the abstract commodity of the factory

The factory has uploaded Abstract goods , Seven cattle , Ali , Tencent's three specific commodities are inherited upload Abstract commodities

Using a procedure is to call a factory's static method , For parameters switch Judge , Depending on the parameters , Instantiate different specific commodity objects , Then call the upload method of the specific commodity object , Upload

advantage ：

The client only needs to know the corresponding parameters of this class

  shortcoming ：

Classes that can be created can only be considered in advance , If you need to add a new class , Then you need to change the factory class

Against the principle of opening and closing （ Open to expansion , Turn off for changes ）, For the addition of new products , Factory class also needs to be modified

More and more specific products , There may be requirements for factory classes to create different instances based on different conditions ． This judgment of condition is interlaced with the judgment of specific product type , Not conducive to maintenance and expansion

Factory method model ：

Factory interface , Factory realization , Abstract product , Specific products

Factory method pattern is the further abstraction and promotion of simple factory pattern

The use process is to instantiate seven cows , Factories of Alibaba or Tencent , These factories all implement a factory interface , This interface has an upload method , For example, qiniu will rewrite the upload method , The class uploaded by qiniu cloud will be instantiated in the rewrite method , Seven cattle cloud upload

advantage ：

The client only needs to know the factory class for creating specific products

Define an interface for creating objects , Let the class that implements this interface decide which class to instantiate . Class instantiation is deferred to subclasses , Using object-oriented polymorphism and the principle of Riemannian substitution , When the program is running , The subclass object will override the parent object , This makes the system easier to expand

Comply with opening and closing principle , Every specific product has a factory , For the addition of new products , Just add a factory to create new products , This factory inherits from the abstract factory , There is no need to change the original code , High maintainability

shortcoming ：

  Increased the number of classes , When there are thousands of types of products , You need thousands of factories

Abstract factory pattern ：

Abstract factory , Specific factory , Abstract product , Specific products

Abstract factory pattern , Also known as toolbox mode

The abstract factory pattern is an upgraded version of the factory method pattern

Introduce plant hierarchy , It solves the problem that factory responsibilities are too heavy in the simple factory model

Make some related products into a product family （ A family of products with functions associated with different product hierarchies ）, To produce by the same factory , This is the basic idea of abstract factory pattern . It also solves the problem that each factory in the factory method mode only produces one kind of products , It may result in a large number of factory classes in the system , The problem of increasing system overhead

advantage ：

It is convenient to add different specific factories for fixed types of products . For example, production win System goods , Just create another production win The factory of the system commodity can

The product family can be constrained inside the class , Instead of introducing a new class for management

When multiple objects in a product family are designed to work together , It ensures that clients always use only objects in the same product family

It's convenient to add new product families , There is no need to modify the existing system , Comply with opening and closing principle

shortcoming ：

complex , Readability is not as good as factory method patterns  

The expansibility of product family is not good , If a new product needs to be added to the product family , Almost all factory classes need to be modified . So when using the abstract factory pattern , The division of product hierarchy is very important

Add new product hierarchy trouble , The original system needs to be greatly modified , You even need to modify the abstract layer code , This will obviously cause great inconvenience , Against the principle of opening and closing

The degradation of the factory model

When every concrete factory class in the abstract factory pattern creates only one product object , That is, when there is only one product hierarchy , Abstract factory pattern degenerates into factory method pattern ;

When abstract factory and concrete factory merge in factory method pattern , Provide a unified factory to create product objects , And when the factory method that creates the object is designed as a static method , Factory method mode degenerates into simple factory mode