I have a question about interface and class implementing interface.

This is my code:

interface iMyInterface {
    public iMethod1();
}

public class cMyClass implements iMyInterface {
    public iMethod1() {
        // some code
    }
    protected iMethod2() {
        // some code
    }
}
I would like to create an instance of iMyInterface as this :

iMyInterface i = new cMyClass();
i.iMethod1();
It's ok, but how can I call iMethod2() from my interface instance? Is this working and safe:

((cMyClass)i).iMethod2(