#440 – A Class Can Implement More than One Interface

It’s possible for a class to implement more than one interface.

For example, a Cow class might implement both the IMoo and the IMakeMilk interfaces.  Multiple interfaces are listed after the class declaration, separated by commas.

    public class Cow : IMoo, IMakeMilk
    {
        public void Moo() { // do mooing here }
        public double Milk() { // do milking here }
    }

You can now use an instance of the Cow class to access members of either interface.

            Cow bossie = new Cow("Bossie", 12);

            // Call both IMoo and IMakeMilk methods
            bossie.Moo();                        // IMoo.Moo
            double numGallons = bossie.Milk();   // IMakeMilk.Milk

We can also set interface variables of either interface type to refer to an instance of a Cow.

            IMoo mooStuff = bossie;
            IMakeMilk milkStuff = bossie;

            mooStuff.Moo();
            numGallons = milkStuff.Milk();