Refactoring: Replace Conditional with Polymorphism

[manuel aldana]

hi,

i read through fowler's refactoring: Replace Conditional with Polymorphism.

fowler presents this kind of solution:

int payAmount(Employee emp){
   ...
   switch (getType()){
       case EmployeeType.ENGINEER;
           return emp.foo();
       case EmployeeType.MANAGER;
           return emp.foo()+1;
       ....
   }
}

but why isn't fowler going even further and uses 'instanceof':

int payAmount(Employee emp){
   ...
   if(emp instanceof EmployeeEngineer)
       return emp.foo();
   if(emp instance of EmployeeManager)
       return emp.foo()+1;
     ....
   }
}

to me the latter code is a better solution. does anybody know why fowler is not going for the more typesafe 'instanceof'? he must have had a reason...

thank you.

[Ilja Preuss]

The code you quoted is not the solution, it's the original, unrefactored code. The solution uses polymorphism instead of the switch statement.

[manuel aldana]

oops,

i got a bit confused (because i read some lines not properly). it makes sense now.
of course payAmount() gets declared abstract in the superclass, subclasses implement it and switch statement gets kicked out.

thanks.