C# OOP 实践混淆 inheritance

Question

I am reading one of my C# programming course material. I understand the code itself, but I don't quite understand why the tutor organises the class this way.

namespace GradeBook
{



public delegate void GradeAddedDelegate(object sender, EventArgs args);
public class NamedObject 
{
    public NamedObject(string name)
    {
        Name = name;
    }

    public string Name
    {
        get;
        set;
    }
}

public interface IBook
{
    void AddGrade(double grade);
    Statistics GetStatistics();
    string Name { get; }
    event GradeAddedDelegate GradeAdded;
}

public abstract class Book : NamedObject, IBook
{
    public Book(string name) : base(name)
    {
    }

    public abstract event GradeAddedDelegate GradeAdded;
    public abstract void AddGrade(double grade);
    public abstract Statistics GetStatistics();
}

public class DiskBook : Book
{
    public DiskBook(string name) : base(name)
    {
    }

    public override event GradeAddedDelegate GradeAdded;

    public override void AddGrade(double grade)
    {
        using(var writer = File.AppendText($"{Name}.txt"))
        {                
            writer.WriteLine(grade);
            if(GradeAdded != null)
            {
                GradeAdded(this, new EventArgs());
            }
        }
    }

    public override Statistics GetStatistics()
    {
        var result = new Statistics();

        using(var reader = File.OpenText($"{Name}.txt"))
        {
            var line = reader.ReadLine();
            while(line != null)
            {
                var number = double.Parse(line);
                result.Add(number);
                line = reader.ReadLine();
            }
        }

        return result;
    }
}

The code snippet above is a GradeBook for normal students.

1. class NameObject defines a property Name and an initializer, which is easy to understand.
2. He put all method in an interface IBook , and there is another class called Book , which is inherited from NameObject class and interface IBook . I am assuming he deliberately separate properties and methods, event. Is this correct?
3. In the Book class, the initializer public Book(string name): base(name) . I know the base is defining a reference type. I am getting a bit confused with the name parameter. Does it refer to the property Name in NameObject ?
4. DiskBook is a subclass of Book, the initializer public Book(string name): base(name) is passing a reference name as the last one. Does the name here refers to the name property in NameObject as well?

Thanks in advance.

Answer 1

2. Logically, a lot of things could be a NamedObject . He's saying a Book is an IBook , and also a NamedObject . Imagine adding a Person class. That Person would be a NamedObject , but not an IBook . So you can reuse the base class without tying it to a Book

3. using : base(name) says call the constructor on the base class with this parameter . So you can be sure that NamedObject 's constructor will be called with the string value, setting the Name property. Excluding the : base(name) from the Book constructor will cause a compiler error, as the base class does not have a parameterless constructor.

4. In the same manner, DiskBook is using : base(name) to call the constructor on Book , which in turn calls the constructor on NamedObject .