c＃oops为什么不在示例代码中打印d

Question

Below code gives the output as "abc".

Please can someone explain why its not printing "d"

public class a
{
    public void m1(a obj)
    {
        Console.WriteLine("a");
    }
}

public class b :a
{
    public void m1(b obj)
    {
        Console.WriteLine("b");
    }
}

public class c: b
{
    public void m1(c obj)
    {
        Console.WriteLine("c");
    }
}

public class d: c
{
    public void m1(d obj)
    {
        Console.WriteLine("d");
    }
}

class MainRunning
{
    static void Main(string[] args)
    {
        a a1 = new a();
        b b1 = new b();
        c c1 = new c();
        d d1 = new d();

        d1.m1(a1);
        d1.m1(b1);
        d1.m1(c1);

        Console.ReadLine();
    }
}

Answer 1

The method printing d is awaiting the instance of type d as its argument. No of your calls passes d to the method called m1 , so other overloads are used.

You can call d1.m1(d1) , which will resolve in m1(d obj) method call, which will write d into your console.

Answer 2

You have 4 methods with the same name but different argument lists. You call three of them, but not the fourth.

Answer 3

It's because you don't call

d1.m1(d1);

When you call d1.m1(b1); then only method that can be run with that param (b1) is the one contained in b class.
And for very of the three methods you run, only one class at a time can handle it and this class is not d class which accepts a different parameter type!!

Answer 4

Please see below:

class MainRunning
{
    static void Main(string[] args)
    {
        a a1 = new a();
        b b1 = new b();
        c c1 = new c();
        d d1 = new d();

        d1.m1(a1);
        d1.m1(b1);
        d1.m1(c1);
        d1.m1(d1); // <== ?

        Console.ReadLine();
    }
}