UML Class Method From Sequence Diagram

Question

How does the direction of a message could determine the method of a class (of a sequence diagram actor) ? I'd say the actor sending the message is the one having the method. Am I correct ?

And the classes For that are

Am I right or is it the other way around ?

Answer 1

"Sending a message" is in most cases the same as "calling a method", which means that if an actor sends a message to the computer, then the computer needs to understand it / implement a method.

There is a difference (see here 1) but essentially you "send a message" to an object, and the object decides what to do with it, in most cases it implements an appropriate method.

So to answer your question, the receiver of the message send should implement a method for it, not the sender.

Perhaps a pseudocode can also illustrate it:

class A {
    function hello() {
        b.someMessage();
        c.otherMessage();
    }
}

class B {
    function someMessage() {
        this.selfMessage();
    }
}