Detailed explanation of Java object oriented design pattern (4), appearance pattern

Irving the procedural ape 2020-11-06 21:30:01
detailed explanation java object oriented


Appearance mode Facade

Appearance mode content is relatively simple , No new examples . This article is excerpted from id=" The definition and characteristics of appearance pattern "> The definition and characteristics of appearance pattern

appearance (Facade) Definition of pattern : Is to provide a consistent interface for multiple complex subsystems , Patterns that make these subsystems more accessible . This mode has a unified external interface , External applications don't care about the details of the internal subsystem , This will greatly reduce the complexity of the application , Improved program maintainability .

appearance (Facade) The pattern is “ Dimitar's law ” Typical application of , It has the following main advantages .

  1. Reduce the coupling between the subsystem and the client , So that changes to the subsystem do not affect the client class that invokes it .
  2. Shielding subsystem components from customers , It reduces the number of objects handled by customers , And make it easier to use the subsystem .
  3. Reduce the compilation dependency in large software systems , It simplifies the migration process of the system between different platforms , Because compiling a subsystem doesn't affect other subsystems , It doesn't affect the appearance of the object .

appearance (Facade) The main disadvantages of the pattern are as follows .

  1. It's not a good way to restrict customers from using subsystem classes .
  2. Adding a new subsystem may need to modify the appearance class or the client's source code , Contrary to “ Opening and closing principle ”.

The structure and implementation of appearance pattern

appearance (Facade) The structure of the pattern is simple , It mainly defines a high-level interface . It contains references to various subsystems , The client can access the functions of each subsystem through it . Now let's analyze its basic structure and implementation method .

1. The structure of the pattern

appearance (Facade) The pattern includes the following main characters .

  1. appearance (Facade) role : Provide a common interface for multiple subsystems .
  2. Subsystem (Sub System) role : Realize some functions of the system , Customers can access it through the facade role .
  3. Customer (Client) role : Access the functions of each subsystem through a look and feel role .

 Structure diagram of appearance pattern

2. The realization of pattern

The implementation code of appearance pattern is as follows :

// Appearance role class Facade{ private SubSystem01 obj1=new SubSystem01(); private SubSystem02 obj2=new S.........
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