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This article is the second article in the design pattern series. Although I wrote the corresponding article before, it was broken for various reasons, and I found that the content written before was also very bad and not systematic enough. So now I plan to rewrite it, plus it's been a while since I started, so it's my own review!

Learning and learning from time to time, not also said.

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Let's Go!

preface

Design patterns are not syntax, they are clever ways to make programs more flexible. Architecture patterns are larger than design patterns, architecture patterns are strategic, and design patterns are tactical.

There are three types of design patterns: creative, behavioral, and structural, totaling 23.

Simple Factory Model

Simple factory design pattern belongs to creation design pattern, but it does not belong to the scope of 23 design patterns. It belongs to the introduction pattern of factory method among 23 design patterns, also called static factory method pattern.

A simple factory pattern is an instance of a factory object that determines which product class to create. Its advantage is hidden object creation, do not rely on objects, you can replace objects at will.

In the factory pattern, all methods in the factory class return the same abstract product class. Code upgrades and extensions only need to inject new functional methods into the factory class, return the abstract product class, or write another interface, and force the abstract product class to be converted into this interface, so that the specific product class can implement it.

business needs

If you were asked to design a simple calculator that could do simple addition, subtraction, multiplication and division of two digits, how would you design it?

code implementation

Just received the demand you, absolutely will find that the demand is so easy(very easy), brush to complete the task.

The idea is simple: an arithmetic class to compute the result, and a calculator class to interact with and receive parameters.

The finished code is as follows

Let's run it through and see what happens.

Is it very simple, haha, I am really a genius (narcissism), after writing looking at their own code, always feel that it seems inappropriate.

Java is characterized by object-oriented, and object-oriented three characteristics are encapsulation, inheritance and polymorphism. I seem to only use encapsulation here, will be a simple operation class encapsulation, but inheritance and polymorphism is not reflected... If the code is submitted in this way and is seen by the leader(leader), it will not be dragged out and shot. No, it will have to be changed again.

After the revision, the Operation code is as follows

(PS: here is only for convenience, so the declaration is an internal class, do not write like this when actually developing similar programs, because if the program becomes complex, this way of writing is not conducive to maintenance)

A simple factory class has been created to implement business logic.

Calculator classes changed little

Try the new calculator and see what happens.

This should not be a problem with submitting code.

In the new version of the code, you just need to type the operator, the factory instantiates the appropriate object, and the calculator's results are implemented by polymorphism, returning the parent class. At the same time, if you need to maintain the program in the future, such as maintaining the addition class, you only need to provide the code of the new method, and you don't need to provide all the code, which improves the security of the whole project.

Simple Factory Pattern UML Class Diagram

summary

Factory: Use a separate class to do the process of creating instances of this class. This is the factory.

The simple factory pattern solves the problem of object creation.

When we know certain conditions for the selection of classes that are subclasses of the same parent class, then we can use the simple factory pattern.

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