Learning experiences on how to design reusable software from three aspects: class, API and framework

Catalog

Software reuse

Classification of software reuse  

Three aspects of software reuse        

1. class

 2.API

2. frame

The reuse type of the framework

summary

---

Software reuse

Software reuse is to use all kinds of knowledge about existing software to build new software , To reduce the cost of software development and maintenance . Software reuse is an important technology to improve software productivity and quality .

Early software reuse was mainly code level reuse , The reused knowledge refers to the program , Later it expanded to include domain knowledge 、 Development experience 、 Design decides 、 Architecture 、 demand 、 Design 、 Code and documentation and everything .

Classification of software reuse  

Software reuse is mainly divided into code level reuse 、 Component level reuse 、 Module level reuse and architecture level reuse , Software reuse is to regard software as composed of different functional parts “ Components ” An organism composed of , Each component can be designed as a general tool to complete the same kind of work , such , If the components that do all kinds of work are established , The task of writing a particular piece of software becomes a simple problem of organizing different components into connectors , This will fundamentally change the final quality and maintenance of software products . Software reuse can reduce development costs 、 Effectively improve the development level , This technology is also the inevitable stage of the current software technology development .

Three aspects of software reuse        

1. class

It is the basis of information encapsulation in object-oriented programming . Class is a user-defined reference data type , Also known as class type . Each class contains a data description and a set of functions that manipulate data or deliver messages . An instance of a class is called an object . It is actually a reference data type , Its essence is to represent a data type , It is the abstraction of a class of things with common characteristics in real life , Class encapsulates the properties and methods used to manipulate its own members , These methods are programs and procedures that operate on this object , The composition of a class includes member properties and member methods , The software reuse methods based on classes are inheritance and delegation , Inheritance is to extend a base class or override an operation through a new operation , A delegate captures an operation and sends it to another object , At the class level , With inheritance , You can make the subclass have the properties and methods of the parent class , It's also a kind of reuse , It can even be said to be a very important reuse , Subclasses do not have to use certain methods . And for the delegate method , stay java Class directly calls this class's static Method , similar c Functions in language , Call directly , This is also a kind of reuse , Similar ones Math.sprt() The call and use of this method .

 2.API

Application programming interface , It is some predefined functions , Or it refers to the agreement on the connection of different components of the software system . A set of routines that applications and developers can access based on a software or hardware , Without accessing the original code , Or understand the details of the internal working mechanism .API Connecting data in different formats . Each data format requires different data commands and parameters to achieve correct data communication , But there are also different types of errors . therefore , In addition to the knowledge required to perform data sharing tasks , These types of API Many network parameter problems and possible error conditions have to be solved , That is, every application must know whether it has strong performance to support the communication between programs . On the contrary, because of this API Only one information format , So information delivery in this case API Only small commands are available 、 A subset of network parameters and error conditions . deliver API This method greatly reduces the complexity of the system , So when an application needs to share data through multiple platforms , Using information delivery API Type is the ideal choice .API Designed to be small 、 complete 、 Simple and clear , Make the calling code easy to remember 、 High readability , secondly ,API To follow LSP principle , That is, if for each type it is T1 The object of o1, All of them are of type T2 The object of o2, So that T1 All programs defined P In all objects o1 All generations into o2 when , Program P There is no change in behavior , So the type T2 It's the type T1 Subtypes of . And it is also necessary to realize that all the places that reference the base class must be able to use the objects of its subclasses transparently . All in all ,API The ground reuse technology has a great development prospect , But at the same time, the above-mentioned specifications shall be fully considered in the design ,

2. frame

Is a group of concrete classes 、 abstract class 、 And the connection between them According to framework The statute of , Fill in your own code , Form a complete system . The framework is usually extended by selective coverage ; Or programmers can add special user code to provide specific functions . We define the framework from the aspects of application and purpose ：

Application aspect ： A framework is a reusable design of a whole or part of a system , It represents a group of abstract components and methods of interaction between component instances .

Purpose ： The framework is an application framework that can be customized by application developers .

Users can extend the framework , But its code should not be modified . In order to increase the reusability of code , You can use delegation and inheritance mechanisms . meanwhile , In the process of using these two mechanisms to increase code reuse , We also add relationships between different classes accordingly （ Delegation or inheritance relationship ）. And for a project , The dependencies between different classes can be regarded as a framework . A large-scale project may consist of many different frameworks . Common frameworks are similar to spring Frame this ,spring The framework code cannot be modified but has DI,IOC, It is convenient for users to create objects , When to create an object , Leave it to the system to judge , Users only need to use objects .

The reuse type of the framework

White box reuse ： The source code is visible , Modifiable and extensible , Copy the existing code when the system under development , Make changes
advantage ： High degree of customization
shortcoming ： Modifying it increases the complexity of the software , And need to fully understand its internal
Black box reuse ： The source code is not visible , Do not modify , Only through API Interface to use , Unable to modify code
advantage ： Simple and clear
shortcoming ： Poor adaptability        

summary

Software reuse will be further developed in the future under the current software development environment , How to better run the engineering thought is reasonable 、 The scientific application of these reuse technologies to create more perfect software engineering will also be a larger research topic , As a student majoring in Software Engineering , It is also necessary to understand and practice the reuse method pattern , Do a good job of excellent design thinking foundation for our career development .