What is? UML Class diagram
- Class Diagram: Used to represent class 、 Interface 、 The static relationship between instances
- Although the name is class diagram , But there are not only classes in the class diagram
Memory skills
UML Arrow direction ：
From child to parent
I Believe Many students will have the same idea as me , Think that subclasses are based on parent classes , The arrow should point from the parent class to the child class
So how do we remember ？
- Subclasses need to be defined through extends Keyword to specify the parent class
- The subclass must know the definition of the parent class , But the parent class doesn't know the definition of the subclass
- Only by knowing the definition of the other party can we point to the other party
- So the direction of the arrow is that the subclass points to the parent
The meaning of line
Solid line --> Inherit Dotted line --> Realization
- You can see Wild geese are a class An interface implemented It points to the interface Because the interface doesn't know the definition of geese
- Duck is the parent of Donald Duck is just a subclass So it points to the parent duck
How to remember ？
- The hollow triangle represents ： To inherit or implement
- Realization - Inherit ： is a The relationship between , Extended purpose , Don't empty , It's very strong
- Dotted line - Realization ： The dotted line represents ‘ Need to be ’ No entity
Solid line --> relation Dotted line --> rely on
- The relationship is stable , A real relationship , Iron elder brothers
- Indicates that one class object is associated with another class object
- Usually, there is another class object in a class as an attribute
- You can see The emergence of penguins is related to the climate So they are related
- Dotted line --> rely on
- Use it temporarily , be neither friendly nor aloof , with no reality whatever , not much , if any
- Represents a usage relationship , One class needs to implement functions with the help of another class
- Generally, one class uses another class as a parameter , Or as a return value
The diamond
- A diamond is a vessel for holding things （ Plates, for example )
polymerization ∶ It means you can put a lot of the same things in an empty vessel , Get together （ The class indicated by the arrow direction ）
Combine ∶ It represents the existence of physical structure in the full vessel , go through thick and thin together
The relationship between the whole and the part
Weak relationship
Negative words : weak - empty
The relationship between the whole and the part , Compared with the relationship of aggregation , The relationship is stronger, and they have the same life cycle ,contains-a The relationship between
A strong relationship
Positive words ∶ strong - full
