A variable is an instantiated object reference of a class. The concept of "person" is a class, the landlord is a special object in "person", and the variable is your name.

Var landlord: Human = new human ("landlord");

Louzhu.sex = "Nanren";

Colon indicates that the landlord of the variable is of human type, and the member attribute of the variable is obtained by dot operator, indicating that the gender of the landlord is = "man". Of course, sex is defined in the "human" class.

The dot operator is usually used when modifying or accessing the properties of an object.

I suggest you read The Road to the Palace, which is of great help to beginners.

The key to getting started is to understand the concept of object-oriented programming. If you don't understand, you can't learn.