UML class diagram

Source: https://blog.csdn.net/a19881029/article/details/8957441

There are 6 types of relationships between classes:

1.  Association is a " has a " relationship

2.  Inheritance is a parent -child relationship

3.  Realization/Implementation

4.  Dependency is a " use a " relationship

5.  Aggregation

6.  Composition

                             

1. Association

One-way or two-way (usually we need to avoid using two-way association relationship), is a " has a " relationship, if A is unidirectionally related to B, it can be said that A has a B, usually expressed as a global variable

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1. publicclass Person {   
2.     public Phone phone;  
3.       
4.     publicvoid setPhone(Phone phone){         
5.         this.phone = phone;  
6.     }  
7.       
8.     public Phone getPhone(){          
9.         return phone;  
10.     }  
11. }  

2.3. Inheritance

A class implements an interface, a class inherits an abstract class, and a class inherits from a parent class belongs to this relationship

4. Dependency

One-way , which means that a class depends on the definition of another class, and changes in one class will affect the other class, which is a " use a " relationship

If A depends on B, then B behaves as A's local variables, method parameters, static method calls, etc.

[java]  view plain copy  

1. publicclass Person {   
2.     publicvoid doSomething(){   
3.         Card card =  new  Card(); //local variable  
4.         ....  
5.     }  
6. }  

[java]  view plain copy  

1. publicclass Person {   
2.     public void  doSomething(Card card){ //Method parameters   
3.         ....  
4.     }  
5. }  

[java]  view plain copy  

1. publicclass Person {   
2.     publicvoid doSomething(){   
3.         int  id = Card.getId(); // static method call  
4.         ...  
5.     }  
6. }  

 

5. Aggregation

One-way, a type of association relationship, the difference between the association relationship is semantic, the two objects associated are usually equal, and the aggregation is generally unequal, there is a sense of the whole and the part, and there is little difference in implementation

Class由Student组成，其生命周期不同，整体不存在了，部分依然存在，当前Team解散了，人还在，还可以加入别的组

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1. public class Team {  
2.     public Person person;  
3.       
4.     public Team(Person person){  
5.         this.person = person;  
6.     }  
7. }  

 

6. 组合关系(Composition)

单向，是一种强依赖的特殊聚合关系

Head，Body，Arm和Leg组合成People，其生命周期相同，如果整体不存在了，部分也将消亡

[java]  view plain  copy

1. public class Person {  
2.     public Head head;  
3.     public Body body;  
4.     public Arm arm;  
5.     public Leg leg;  
6.       
7.     public Person(){  
8.         head = new Head();  
9.         body = new Body();  
10.         arm = new Arm();  
11.         leg = new Leg();  
12.     }  
13. }