Interface inheritance combined with class inheritance

Question

I'm having a problem with a task given and I would like to ask for an advice.

I've been told to implement: IPerson interface Person class based on IPerson IEmployee and Employee extending IPerson and Person

The last sentence made by confused, I have no idea how to cope with that requirements. I have a thought and I'd like it to be verified by You, since Person and Employee will be stored using a List then:

Will IEmployee extend IPerson and Employee just implement IEmployee? or in addition to that Employee should extend Person as well?

Thanks for an answer to this question!

Answer 1

All employees are people, and so all employees implement both IEmployee and IPerson. The Employee class extends the Person class.

public interface IPerson
{
}

public class Person : IPerson
{
}

public interface IEmployee : IPerson
{
}

public class Employee : Person, IEmployee
{
}

Answer 2

This is what you want:

public interface IPerson { }
public interface IEmployee : IPerson { }
public class Person : IPerson { }
public class Employee : Person, IEmployee { }

Answer 3

The question really is that you should think twice before implement interface hierarchies...

You don't want to force interface implementation classes to implement methods that will be not used, so think if methods that use IEmployee as parameters will also need all IPerson properties or not. If not is better to define a new interface with just the needed properties.

This corresponds to Interface segregation of SOLID principles.