UML类图（简介、类的表示、对象的表示、关系、注释）

1. 简介
2. 类和对象
- 2.1 类的表示
- 2.2 对象的表示
3. 关系的表示
- 3.1 依赖关系
- 3.2 作用关系---关联
- 3.3 包含关系---聚集和组合
- 3.4 继承关系-泛化
4. 注释

1. 简介

UML（Unified Modeling Language）是一种面向对象的建模语言，包含我们所需要的所有图形标识；是一种更直观的图形方式，用符号来表示概念，概念间的关系用连接符合的线来表示

UML的各种图形，分别描述软件模型的静态结构、动态行为、模块组织和管理；本文我们讲解的类图（class diagram），是一种静态结构图（static structrue diagrams），用来描述类和对象、类和对象的内部结构、类和对象的关系

2. 类和对象 2.1 类的表示

我们先来看一个简单的例子，体验一下

class Student {
public:
    Student(string n = "",int a=0) {
        name=n;
        age= a;
    }

    void show() {
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.activeCrit1,#mermaid-svg-iaJP9tyxPo5HeNEg .activeCrit2,#mermaid-svg-iaJP9tyxPo5HeNEg .activeCrit3{stroke:#f88;fill:#bfc7ff;stroke-width:2}#mermaid-svg-iaJP9tyxPo5HeNEg .doneCrit0,#mermaid-svg-iaJP9tyxPo5HeNEg .doneCrit1,#mermaid-svg-iaJP9tyxPo5HeNEg .doneCrit2,#mermaid-svg-iaJP9tyxPo5HeNEg .doneCrit3{stroke:#f88;fill:#d3d3d3;stroke-width:2;cursor:pointer;shape-rendering:crispEdges}#mermaid-svg-iaJP9tyxPo5HeNEg .milestone{transform:rotate(45deg) scale(0.8, 0.8)}#mermaid-svg-iaJP9tyxPo5HeNEg .milestoneText{font-style:italic}#mermaid-svg-iaJP9tyxPo5HeNEg .doneCritText0,#mermaid-svg-iaJP9tyxPo5HeNEg .doneCritText1,#mermaid-svg-iaJP9tyxPo5HeNEg .doneCritText2,#mermaid-svg-iaJP9tyxPo5HeNEg .doneCritText3{fill:#000 !important}#mermaid-svg-iaJP9tyxPo5HeNEg .activeCritText0,#mermaid-svg-iaJP9tyxPo5HeNEg .activeCritText1,#mermaid-svg-iaJP9tyxPo5HeNEg .activeCritText2,#mermaid-svg-iaJP9tyxPo5HeNEg .activeCritText3{fill:#000 !important}#mermaid-svg-iaJP9tyxPo5HeNEg 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:root { --mermaid-font-family: "trebuchet ms", verdana, arial;}
  #mermaid-svg-iaJP9tyxPo5HeNEg {
    color: rgba(0, 0, 0, 0.75);
    font: ;
  }
  
  
   
    
   
  
  
   
    
   
  
  
   
    
   
  
  
   
    
   
  
  
   
    
   
  
  
   
    
   
  
  
   
    
   
  
  
   
    
   
  
  
   
   
    
     Student

 
数据成员的表示 
  语法： [访问控制属性]名称 [重数] [: 类型] [= 默认值] [{约束特征}]
访问控制属性：public、private、protected分布对应UML的"+"、"-"、"#"
名称：数据成员的变量名
重数：属性的重数，具体什么意思没搞懂
默认值：如该数据成员的类型为Area，Area类构造函数为Area(int length, int width)，则该数据成员的默认值形式为= (10, 10)
约束特征：该数据成员性质约束的说明，如{只读}表示该数据成员只能被读取
  
2.2 对象的表示 
我们用上面的类Student创建一个对象my_student  说明： 
分为两部分，上面部分为对象名，下面部分为数据成员及其值，数据成员及其值是可选的
对象名格式为：对象名 : 类名，下面要加下划线，可以省略对象名或类名 
3. 关系的表示 
使用带有特定符号的实线段或虚线段表示关系 
3.1 依赖关系 
表示一个类A使用另一个类B作为函数的成员参数，就要用依赖关系，通常为类之间的调用、友元和类的实例化；B变化会影响A，反之不成立 
UML中表示依赖关系使用构造型，如下所示：  表示类A使用了类B 
3.2 作用关系—关联 
表示一个类的对象和另一个类的对象之间相互作用的关系，UML中用实线来表示两个类（或同一个类）之间的关联  重数A表示：类B的每个对象与类A的多少个对象发生作用，如：重数A = 0..1 重数B表示：类A的每个对象与类B的多少个对象发生作用 
重数标记的形式和含义如下表所示： 
标记说明*任何数目的对象(包括0)1恰好1个对象n恰好n个对象0…10个或1个对象(表明关联是可选的)n…m最少为n个对象, 最多为m个对象(n和m是整数)2,4离散的结合(如2个或4个)
3.3 包含关系—聚集和组合 
聚集表示整体与部分的关系，是一种特殊的关联，聚集分为共享聚集和组成聚集（组合），如下所示：  
左图表示共享聚合：类A包含多个类B，但类B还可以被其它类包含，在UML中由空心菱形表示
右图表示组成聚合（组合）：类A包含多个类B，且类B只能被类A包含，在UML中由实心菱形表示 
3.4 继承关系-泛化 
类的继承关系在UML中称为泛化，如下图所示，子类1说明单继承，子类2说明多继承  
4. 注释 
UML的注释是一种能独立存在的修饰符号，附加在元素或元素集上用来表示说明的图形符号，可以添加说明、评述、注解等信息，如下所示：  其中虚线连接到UML的其它元素上

UML类图（简介、类的表示、对象的表示、关系、注释）

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