Let me tell you a few questions first

1. You use a type parameter T to inherit PetHospital. The type of T may be Hippiater, Customer, Pet, etc. This inheritance method violates the "is-A" semantics of inheritance. Imagine that a customer or a pet is a PetHospital?

2. Web Zeng can certainly understand the objects in the bean layer, because the parameters of your web layer generally come from the form, so naturally you must know what object the form is for. Controllers in struts or spring are used directly and encapsulate form parameters into bean layer objects.

3. The delete method only accepts an id, so how do you know what object needs to be deleted? Is it a customer? Or a pet? What if these two have the same id?

If you must use a generic type, refer to the following code

public class Entity {
    private String id;
    //omit getter and setter
}

public class Pet extends Entity{
    private String name;
}

public interface EntitiyService<T extends Entity> {
    boolean addOne(T arg);

    boolean deleteOne(int id);

    List<T> list(int page);
}

public class EntityServiceImpl<T extends Entity> implements EntitiyService<T> {
    @Override
    public boolean addOne(T arg) {
        System.out.println("save entity " + arg.toString());
        return true;
    }

    @Override
    public boolean deleteOne(int id) {
        System.out.println("delete entity which type is T");
        return false;
    }

    @Override
    public List<T> list(int page) {
        System.out.println("query first " + page + " pages result");
        return null;
    }
}

public class Client {
    public static void main(String[] args) {
        Pet petFromForm = new Pet();
        EntityServiceImpl<Pet> entityService = new EntityServiceImpl<>();
        entityService.addOne(petFromForm);
        entityService.deleteOne(1);
        entityService.list(3);
    }
}