CS3: PROGRAMMING PATTERNS

		         EXAM #2

name: first ________________   last _____________________

The number of points for each question is given in square
brackets. State your assumptions. Explain your code.

1. [10] Draw a UML class diagram for the following 
   class definitions.

   class A{
   };

   class B{
   public:
     virtual int myfunc();
   protected:
      int x_;
   private:
      A* a_;
   };

   class C: public B{
   public:
      int myfunc();
   };


2. [15] Explain the purpose of Singleton Design Pattern.
   Differentiate between Meyer's and Classic Singleton Design Pattern
   Implementation. Provide code for the instance() function for one
   the implementations and explain the operation of this function.

3. [10] Describe what virtual function is. Explain polymorphism. Differentiate
   between run-time and compile-time binding.  Given following code in main()

      A *p = new B;
      p->myfunc():

   Complete below class definitions such that myfunc() invoked
   above is a feature of class B. Explain your code.

      class A{
      };

      class B: public A{
      };


4. [15] Differentiate between class interface and class
   implementation. Contrast public and private inheritance with
   respect to class interface and implementation.

   Describe Adapter Design Pattern. Describe Adapter, Adaptee and
   Target Interface classes. Given the code below, provide definition
   of the Adapter class for the class-based Adapter design
   pattern:state class inheritance and provide myFunc() implementation
   in terms of yourFunc(), the implementation is of your
   choice. Provide example of client usage of your pattern (invocation
   of the implemented function).

   class TargetInterface{
   public:
        void myFunc();
   };

   class Adaptee{
   public:
        void yourFunc();
   }


5. [15] Explain the purpose of State design pattern. Explain the purpose of
  context class, abstract state class and concrete state class. Given
  the code below, explain the relationship between changeState in
  class Context and class State. Provide outside (of class)
  implementations of both functions.

   class Context{
        void changeState(State *s);
   private:
        state* s_;
   };

   class State{
        void changeState(Context *c, State *s);
   };


6. [10] Explain the purpose of Prototype design pattern. Explain what
   function clone() does. Given the following abstract class, provide
   a concrete implementation (define the clone() implementation) and
   provide an example of use by a client.

   class Prototype{
   Public:
       virtual Prototype* clone();
   };

7. [15] Explain the purpose of Decorator Design Pattern.  Write code
   that decorates the below ChrsitmasTree with ornaments (modifies the
   stored string). Give example code that invokes show() to print out
   the decorated tree.

      class ChristmasTree{
      public:
        ChristmasTree:tree_("_\|/_"){} // initializes the tree
        virtual string show() const{return tree_;}
      private:
         string tree_;
      };


8. [10] Explain the purpose of Observer Design Pattern. Explain why it
   is also called Publish/Subscribe. That is, what is being published
   and subscribed to in this design pattern?  Give an example
   programming task where this pattern might be used.