CSC 313 – Advanced Programming Topics

Lindsay Lohan Economy  Studies investigated economy of celebrities  Direct earnings from movies, music, TV, ads  Profits earned by her label, handlers, etc.  Photographers’ income for pictures on TMZ  When placed on cover, increase in magazine sales  $150+ million/year industry for top celebrity

Something about Lindsay  Is it her singing?

Something about Lindsay  Is it her singing?  Acting key to her success?

Something about Lindsay  Is it her singing?  Acting key to her success?  Her keen fashion sense?

Something about Lindsay  Is it her singing?  Acting key to her success?  Her keen fashion sense?  Long, slow, very public total breakdown?

Something about Lindsay

How Lindsay Does It  Millions interested in seeing this unfold  Each and every mistake,  Every outburst that she makes,  And, of course, what or whom she is dating  Could follow her to be around for each event  But may have job, school, or restraining orders  Lindsay uses Observer Pattern for attention & $$$

Observer Pattern  Observers subject  Observers want update when subject changes  Must manage this 1:many relationship  Efficiently communicate all of these updates ConcreteSubject stateChanged() : boolean setChanged() : void

Foundation of an Industry  Lindsay notifies paparazzi before going out  With notice, photographers go to her destination  Take incriminating pictures of her doing her thing  With pictures takes, paparazzi notify press  Some published in magazines & used on Dr. Phil  Others will get posted to blogs  “Private use” of individuals for some pictures  Entire crisis then unfolds for enquiring minds

Textbook Observer Pattern  Readers sent People when it is printed  Readers  Readers are observers People magazine  Subject is People magazine (in this case)  Whenever subject updated, observers notified  Magazines notified of pics paparazzi took People  In this relationship, People is an observer each photographer  Subject is each photographer

Textbook Observer Pattern  Paparazzi alerted by Lindsay before leaving  Lindsay  Lindsay is ultimate subject (& pattern master) Paparazzi  Observers in this relationship are Paparazzi

True Genius  Very efficient way for Lindsay to get money  Also has benefit of limiting people following her  Readers notified of each and every change readers  In this adventure, readers observers only  Lindsay  Lindsay only a subject in this implementation  Magazines photographers  Magazines & photographers play both roles  Observer Pattern mastered for this to work

True Genius

Observer Is Hollywood  Hollywood Principle: Don’t Call Us, We’ll Call You  If observers were to ask constantly “Are we there yet? Are we there yet?”  Really slow when many observers exist  Principle says to have subject send alerts  Articles only after craziness on Lindsay’s part  When no DUIs, covers with Kate Gosselin instead

Co-Dependent Relationships  UML class diagrams with cycles are problem  Two classes inseparable no matter what  Classes completely dependent on each other  Almost impossible to add or extend the design  Since both classes needed, reusing one impossible

Replace Cycles With Observer  Cycle still in UML class diagram…

Replace Cycles With Observer  Cycle still in UML class diagram…  … but now classes depend only on interfaces  Classes can be replaced at any time  Only requires that new class implement interface  Far easier to add or modify classes now

For Next Lecture  Read pages 56 – 69 in book  Great… so how do we code the observer pattern?  Haven’t I seen this pattern before?  How is it actually written in the real world?  Is it really this simple and powerful?