[UML] several relationships of UML (dependency Association aggregation composition inheritance Implementation)

UML Several relationships ：

2.1 Dependency relationship (Dependency)

Dependency is a kind of usage relationship , A change in a particular thing may affect other things that use it , In need of representation
One thing uses another Use dependencies when . Most of the time , Dependency is reflected in the fact that the methods of one class use the objects of another class as parameters .
stay UML in , Dependencies are represented by dotted lines with arrows , from The dependent party points to the dependent party .

Dependency instances
In the system implementation phase , Dependencies are usually implemented in three ways

• The first and most commonly used method is to take the object of one class as the parameter of the method in another class as shown in the figure
• The second way is to take the object of another class as its local variable in the method of one class
• The third way is to call another class middle note in a class method.

2.2 Connections (Association)

The most commonly used relationship between classes , It's a structured relationship , be used for Indicates that there is a connection between one type of object and another
Such as cars and tires 、 Master and apprentice 、 Classes and students, etc .
stay UML In class diagram , Use a solid line to connect the classes of objects that are related
In the use of Java When implementing an association , Usually Take the object of one class as a member variable of another class
When using the class diagram to represent the association relationship, you can mark the role name on the association line , Generally, a verb or noun indicating the relationship between the two is used to indicate the role name （ Sometimes the noun is the instance object name ）, The two ends of the relationship represent two different roles , Therefore, two role names can be included in an association relationship , The role name is not required , You can add... As needed , The purpose is to make the relationship between classes clearer .