Question

I cannot understand this piece of code:

 public class BookCategory
 {
     public string CategoryName { get; set; }
     public List<Book> Books { get; set; }
 }
 public class Book
 {
     public string Title
     {
         get;
         set;
     }
 }

What does it mean List<Book>, and does it inherit from class Book or not ?

Answer 1

List<Book>^[MSDN] is a generic collection of Book objects. It doesn’t inherit from Book. Rather, it contains zero or more Book objects in a collection.

Because the List<T> class is generic, it can be reused to provide list operations on a collection of any type of object. You can have List<int>, List<string>, List<object>, etc., but they all work from the same List<T> class, which is a great example of the DRY principle (Don’t Repeat Yourself). In this example, T is called the type parameter and can be any .NET or user-defined type.

You can define you’re own generic classes. Here’s a trivial example of the syntax:

public class Foo<T>
{
    public T AnObject { get; set; }

    public Foo(T anObject)
    {
        AnObject = anObject;
    }
}

Some other very useful .NET generics are:

• Stack<T>^[MSDN]
• Queue<T>^[MSDN]
• Nullable<T>^[MSDN]
• Dictionary<TKey,TValue>^[MSDN]
• and many more…

Generics are very useful and pervasive in .NET, so definitely familiarize yourself with this concept.