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

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