以下继承之间有什么区别

Question

Here is the simple inheritance

public class BaseClass
{
    public string Draw()
    {
        return "Draw from BaseClass";
    }
}

public class ChildClass:BaseClass
{
    public string Draw()
    {
        return "Draw from ChildClass";
    }
}

static void Main(string[] args)
{
   ChildClass c = new ChildClass();
   console.writeline(c.Draw());
}

The above implementation will print Draw from Childclass

Here is the usage with the override

public class BaseClass
{
    public virtual string Draw()
    {
        return "Draw from BaseClass";
    }
}

public class ChildClass:BaseClass
{
    public override string Draw()
    {
        return "Draw from ChildClass";
    }
}

static void Main(string[] args)
{
   ChildClass c = new ChildClass();
   console.writeline(c.Draw());
}

The above implementation will print Draw from Childclass

So what is the difference between above 2 Inheritance Implementation.

Answer 1

In the second snippet Draw is declared to be virtual, this means that you can call the inherited method from a variable of type BaseClass .

BaseClass b = new ChildClass ();

b.Draw () // will call ChildClass.Draw 

---

Documentation

• msdn - 10.5.3 Virtual methods
• The C# Station Tutorial - Lesson 9: Polymorphism

Funny thing.. the second link in the list above uses the same snippets as you've provided.

Answer 2

In the first implementation, if you call Draw() from inside BaseClass , the output will be "Draw from Base Class". But in the second implementation it will be "Draw from Child Class". Here is an explanation: http://weblogs.sqlteam.com/mladenp/archive/2007/04/09/60168.aspx