The meanings of some symbols in UML are written to enhance memory.

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Figure 1:

This solid-line arrow represents, inherit
Is inherited from a non-interface class.

Figure 2:

That line represents two-way Association
:
On the left side, flight plays the role assignedfights, with 0 to 1 plane associated with him (a flight can either be canceled, no plane, or only correspond to one plane)
On the right side, plane plays the role of assignedplane, with 0 to multiple flight associated with him (one plane can participate in multiple flights or stop in the warehouse and rot)

Figure 3:

That line indicates one-way Association.
:
The basic meaning is the same as above. The only difference is that the class on the right has no idea about the class on the left.

Figure 4:

The large enclosed box is called a software package.
, The name is account, and some classes that can be classified are packaged.

Figure 5:

The dotted arrow represents an interface.
.

Figure 6:

The horizontal line still indicates the association mentioned above, but the dotted line extended from the association line, which means that when an instance of the flight class is associated with an instance of the frequentflyer class, an instance of the mileagecredit class will be generated.
.

Figure 7:

The arrow with a diamond represents the basic aggregation. From the knowledge, the wheel class assumes the role of the wheels and aggregates four to the car object,
The hollow diamond indicates that the wheel object is not created and destroyed with the creation of the car.
.

Figure 8:

The meaning is similar to the above. The only difference is that the solid diamond indicates that the Department object is created and destroyed along with the creation of the company object.
.

Figure 9:

Reflection Association
Shows how an employee class is associated with it through the manager/manages role. When a class is associated with itself, this does not mean that the instance of the class is related to itself, but an instance of the class is related to another instance of the class.