【转载】#437 - Access Interface Members through an Interface Variable

Onece a class implementation a particular interface, you can interact with the members of the interface through any instance of that class.

 Cow bossie = new Cow("Bossie", );

 // Cow implements IMoo, which includes Moo method
 bossie.Moo();

You can also declare a variable whose type is an interface, assign it to an instance of any class that implements that interface and then interact with members of the interface through that interface variable.

 // bossie is a Cow, which implements IMoo, so we can point IMoo variable at her
 IMoo mooer = bossie;
 mooer.Moo();

Notice that we can't access members of Cow that aren't part of IMoo using this interface variable.

 // Can't call Cow methods not in IMoo
 mooer.MakeSomeMilk();

Even though MakeSomeMilk is a public method in the Cow class, we can't access it via IMoo.

原文地址：#437 – Access Interface Members through an Interface Variable