Record a design issue and design issue

Record a design issue and design issue

The requirements are as follows: there is A Class A and A subclass B, C, D

Abstract class A {abstract void fn ();} class B: A {override void fn () {}} class C: A {override void fn () {}} class D: A {override void fn (){}}

 

Obviously, B, C, and D must rewrite their respective fn () to complete their own functions. However, due to similar functions, the fn () Implementations of B, C, and D are almost the same. There are three ways to write this common function:

1. Add A protected member in A and then call it directly in B, C, and D.

2. Rewrite the abstract of A to virtual, and then call it through base. fn () in the subclass.

3. Create a new class and write it as a static function for calling B, C, and D.

Ask the next database design question. How can I set the information fields of the instructors in the school activity table to facilitate the export of activities of individual students?

This is obviously a multi-to-many relationship, so we use the third table to store this relationship.
Instructor information table (Instructor ID, name)
Activity record table (activity ID, name)
The fields of the participating table (Instructor ID and activity ID) are both foreign keys.
 
Teach a VF query designer

It should be clear that the question "male and female in English courses" means that it is definitely not only a class, so what is required here is not only grouping by class number, but also group by gender.
"LEFT (Xuesheng. Student ID, 8) AS class number" and "xuesheng. Gender" should be added after group