Cannot understand setEmployees: method


I am quite confused. I don’t understand what the following code does.
I guess this method is called when the “Add Employee” button is pressed. Is the “add:” action responsible for triggering this method? If that is so, why would “a == employees” be true at any time?

[code]- (void) setEmployees: (NSMutableArray *) a
if (a == employees) {
//NSLog(@“reached a == employees”);
//NSLog(@“reached a != employees”);
employees = a;