int and void refer to the return type of a method, and int refers to the return type being an integer, such as 1 or 0. According to the definition of the interface, 1 should indicate a successful increase or update, and 0 indicates an increase or More detailed failure, return null means that if no information can be found during query, empty will be returned. String refers to a string, and String uName is the value. Query user information based on the uName parameter.

User should be an entity class. User user is used to add or update user information. if(users[i]==null) is used to determine whether the user information exists. If it does not exist, add the user. if(users[i] !=null && users[i].getuName().equals(uName)) is also used to check whether the information exists. If it exists, query or update operations are performed. It is recommended to buy a basic Java book and read it to understand the basic concepts.