1. Design Patterns Difficult to describe abstractly Elements:
Pattern Name
Problem to Solve
Solution
Consequences: Results and Trade-Offs
Higher level abstraction than classes

2. Example: Singleton
Intent: Define a class pattern that is guaranteed to have only one instance, and provide a global point of access to it.
Uses
A good global variable/class
Simulator has one radar, one physical display, etc.

3. Singleton Implementation
Class Singleton {
public:
static Singleton* Instance();
protected:
Singleton();
private:
static Singleton* _instance; };
Singleton* Singleton::Instance = 0;
Singleton* Singleton::Instance() {
if (_instance == 0) {
_instance = new Singleton; }
return _instance;

4. Example: Abstract Factory
Provide and interface for creating families of related or dependent objects without specifying their concrete class.
A system can be created that is independent of how its elements(products) are created, composed, and represented
Participants:
Abstract Factory (WidgetFactory): interface to the client
Concrete Factory(MotifWidgetFactory, MFCWidgetFactory): implements the abstract interface
Abstract Product(Window, Scrollbar): what the client sees
Concrete Product(MotifWindow, MotifScrollBar): defines the actual object
Client: who uses the products via the abstract interfaces

5. Iterator
Goal: Provide a way to sequentially access the elements of an aggregate object without exposing its underlying representation.
Using an iterator, it would be possible to replace an array with a linked list or binary tree
This construct is heavily used in STL

6. Iterator Implementation
Template <class Item>
class Iterator {
public:
virtual void First() = 0;
virtual void Next()= 0;
virtual bool IsDone() const = 0;
virtual Item CurrentItem const = 0;
protected:
Iterator(); };

7. List Iterator Template <class Item>
class ListIterator : public Iterator<Item> {
public:
ListIterator(const List<Item>* aList);
virtual void First(); …
private:
const List<Item>* _list;
long _current; };

8. STL Standard Template Libaray: Part of C++ Objects vector list
map & multimap
set & multiset
deque (double ended queues)
stack, queue, priority_queue

9. STL cont’d All objects have iterators
Generic Algorithms can be done on these objects
for_each, find, count, equal, search, sort, fill, merge, etc.