Design Patterns
                         Strategy Pattern*
                         How to design for flexibility?
                        ebru@hacettepe.edu.tr
                     ebruakcapinarsezer@gmail.com
                   http://yunus.hacettepe.edu.tr/~ebru/
                             @ebru176
                             Ekim 2017
               *revised from, www.uwosh.edu/faculty_staff/huen/262/f09/slides/10_Strategy_Pattern.ppt
 Existing Duck application
     All ducks quack        Duck
     and swim.  The 
     superclass takes       quack()
     care of the            swim()
     implementation                                              The display() 
     code                   display()                            method is abstract, 
                            //other duck-like methods…           since all duck 
    Each duck subtype is                                         subtypes look 
    responsible for                                              different
    implementing its own 
    display() method
                                                                         Other duck 
          MallardDuck                     RedHeadDuck                    types inherit 
                                          display() {                    from the 
          display() {                                                    Duck class
          // looks like a mallard}        // looks like a redhead }      . . . 
  Testing Mallard, RedHeadDuck classes
  Changing Requirment
    • No sweat!
      • Add a method fly() in Duck
      • Continue to use inheritance