当从子类转换为父类来执行方法时,并不是直接编译执行,而是先看该方法是不是虚方法：
①、如是虚方法,则从该对象的实际类型(该子类)开始向 System.Object 回溯，直至找到该方法,再编译执行
②、如不是虚方法,则从直接从该父类开始搜索并向 System.Object 回溯,直至找到该方法,再编译执行
public interface IA {
string SayHello();
}
public class A : IA {
public virtual string SayHello() {
return "A";
}
}
public class B : A {
public new virtual string SayHello() {
return "B";
}
}
public class C : A {
public override string SayHello() {
return "C";
}
}
public class D : B {
public override string SayHello() {
return "D";
}
}
IA ia = new A();
IA ib = new B();
IA ic = new C();
IA id = new D();
ia.SayHello();//"A"
ib.SayHello();//"A"
ic.SayHello();//"C"//原回答这儿有误
id.SayHello();//"A"
A a = new A();
A b = new B();
A c = new C();
A d = new D();
a.SayHello();//"A"
b.SayHello();//"A"
c.SayHello();//"C"
d.SayHello();//"A"
var va = new A();
var vb = new B();
var vc = new C();
var vd = new D();
va.SayHello();//"A"
vb.SayHello();//"B"
vc.SayHello();//"C"
vd.SayHello();//"D"
参考文献：C#子类可以重写父类的方法，为何还要虚方法？ - 知乎 (zhihu.com)
原文：https://www.cnblogs.com/renyan52099/p/14799342.html