Do I need to create interfaces for a single class?

Question

OOP

If necessary, in what cases.

Answer 1

If there is a possibility that the class may be replaced by another in the future or already several classes with a common interface are connected under different conditions

Answer 2

1. If some kind of abstraction can be pulled out of the class. For example, the abstraction "stream" can be pulled out of the "file" object. Private - The Project object implements the Modifiable interface with two functions: modify() and isModified().
2. To simplify unit testing under the condition of ownership.
Suppose we have a class "class" (school) and a class "student". The student knows what class he is in.
In such a situation, a “tangle” is obtained: if you need to make a student, then you need to make a class.
This vicious circle can be broken by making the ISchoolClass interface and deriving a class from it. When unit testing, we replace the class with some kind of stub.

Answer 3

See what class.
If this is the essence of the subject area, then no, it's not worth it.
If these are services, then yes, it's worth it.