1. DEV-08: Exploring Object-oriented Programming
Shelley Chase
Development Architect – Progress OpenEdge

2. Today’s Agenda Basic Principles of Object-oriented Programming
Types, Classes, Objects, and Interfaces
Inheritance, Polymorphism, and Delegation
DEV-08, Exploring Object-oriented Programming

3. What are Objects? You interact with objects everyday
A customer
An order
All objects contains state and behavior
What they can do and what changes when they do
Software objects represent these as:
Data ( like 4GL variables )
Methods ( like 4GL procedures)
Your car
The telephone
DEV-08, Exploring Object-oriented Programming

4. Object-oriented Programming
“Object-oriented programming is a method of implementation in which programs are organized as cooperative collections of objects, each of which represents an instance of some class...”
Grady Booch
DEV-08, Exploring Object-oriented Programming

5. Object-oriented Application Development
A way to design and build applications
Objects bundle together data (state) and methods (behavior)
Objects facilitate separating definition from implementation
Much more than just syntax
You might have already done object-oriented programming in the 4GL
DEV-08, Exploring Object-oriented Programming

6. Designing an Object-oriented Application
Object: Order
Take an Order
Object: Customer
Check Credit
Create a Customer
Object: beOrder
Assign Salesperson
Progress
DataSet
Customer Table
Order Table
Customer
Table
DEV-08, Exploring Object-oriented Programming

7. Basic Object-oriented Principles
Abstraction
Encapsulation
Hierarchies
DEV-08, Exploring Object-oriented Programming

8. Abstraction Abstraction is used to manage complexity
Public View of an Object
Abstraction is used to manage complexity
Focus on the essential characteristics
Eliminate the details
Find commonalities among objects
Defines the public contract
Public definition for users of the object
The “Outside view”
Independent of implementation
DEV-08, Exploring Object-oriented Programming

9. “What should an Order object do?”
Abstraction - Example
“What should an Order object do?”
Object: Order
CreateOrder
UpdateOrder
GetOrderTotal
Next
InternalOrder
Two types of Orders
ExternalOrder
DEV-08, Exploring Object-oriented Programming

10. Encapsulation Encapsulation hides implementation
Hide Implementation Details
Encapsulation hides implementation
Promotes modular software design – data and methods together
Data access always done through methods
Often called “information hiding”
Provides two kinds of protection:
State cannot be changed directly from outside
Implementation can change without affecting users of the object
DEV-08, Exploring Object-oriented Programming

11. Encapsulation - Example
Implementation Outside View
Object: Order
orderNum AS INT
custNum AS INT
CalculatePrice( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
Public methods of Order class
CreateOrder
UpdateOrder
GetOrderTotal
Next
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
DEV-08, Exploring Object-oriented Programming

12. Encapsulation - Example continued
Hmm I’d like to change CalculatePrice to CalculateTotalPrice
Object: Order
orderNum AS INT
custNum AS INT
CalculatePrice( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
GetOrderTotal calls CalculatePrice( )
DEV-08, Exploring Object-oriented Programming

13. Encapsulation - Example continued
Object: Order
This change was easy because users of the object will not be affected.
orderNum AS INT
custNum AS INT
CalculateTotalPrice( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
GetOrderTotal now calls CalculateTotalPrice( )
DEV-08, Exploring Object-oriented Programming

14. Hierarchies Define relationships between objects
Object Relationships
Define relationships between objects
Objects defined in terms of other objects
Allows state and behavior to be shared and specialized as necessary
Encourages code reuse
Two important hierarchy types:
Inheritance
Aggregation
DEV-08, Exploring Object-oriented Programming

15. Hierarchies - Example Order is a is a references InternalOrder
Order uses ShipInfo (Aggregation)
Order
is a
is a
references
InternalOrder
ExternalOrder
ShipInfo
InternalOrder and ExternalOrder inherit from Order (Inheritance)
DEV-08, Exploring Object-oriented Programming

16. Summary : Object-oriented Principles
Abstraction
Break up complex problem
Focus on public view, commonalities
Encapsulation
Hide implementation details
Package data and methods together
Hierarchies
Build new objects by combining or extending other objects
DEV-08, Exploring Object-oriented Programming

17. Today’s Agenda Basic Principles of Object-oriented Programming
Types, Classes, Objects, and Interfaces
Inheritance, Polymorphism, and Delegation
DEV-08, Exploring Object-oriented Programming

18. Type A Type defines the state and behavior Enables strong-typing
A Type is a definition
A Type defines the state and behavior
Identifies inheritance relationships with other types
No concern for implementation
Enables strong-typing
Early binding - types determined at compile time
Type-consistency enforced at compile time and runtime
DEV-08, Exploring Object-oriented Programming

19. Type - Example Types: Order Order InternalOrder ExternalOrder is a
Subtype of Order
ExternalOrder
SubType of Order
Order
is a
is a
InternalOrder
ExternalOrder
A subtype can appear anywhere a super type is expected
DEV-08, Exploring Object-oriented Programming

20. Benefits of Types (Strong-Typing)
Compile time checking for type consistency
myObj = mySubObject. (must be subType)
myObj:method(…). (validates signature)
myObj:data = 3. (validates data type)
Results in safer, bug-free code because all code paths checked at compile time
DEV-08, Exploring Object-oriented Programming

21. Class Class: Order A Class defines and implements a user-defined type
A Class implements a Type
Class: Order
orderNum AS INT
custNum AS INT
CalculateTotalPrice( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
A Class defines and implements a user-defined type
A Class is a template (blueprint) for an object:
Data
Methods
Relationships to other classes
Methods Data
DEV-08, Exploring Object-oriented Programming

22. Object An Object is created at runtime
An Object is an instance of a Class
An Object is created at runtime
Maintains independent state in data members
Code shared among object instances
The term Object is often used to refer to both classes and instances
MyOrder
orderNum = 10
custNum = 3
Total Price = $45.00
YourOrder
orderNum = 61
custNum = 58
Total Price = $318.34
DEV-08, Exploring Object-oriented Programming

23. Interface
An Interface implements a Type
An Interface is a collection of method definitions for a set of behaviors – a “contract”
No implementation provided
A Class can implement an interface
Must implement all methods in the interface
Behavior can be specialized
Compiler validates implementation of interface
DEV-08, Exploring Object-oriented Programming

24. Interface - Example Class Order implements IList interface
orderNum AS INT
custNum AS INT
CalculateTotalPrice( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
Interface: IList
PUBLIC:
Next( )
Compiler checks for method definition in implementing class
DEV-08, Exploring Object-oriented Programming

25. Interface – Example continued
Write generic routine using interface
MoveNext( listObj AS IList )
listObj.Next( ) /* Calls method
in real object */
Call with any object that implements IList
myOrder = NEW Order( ) /* implements IList */
MoveNext( myOrder ). or
myCust = NEW Customer( ). /* implements IList */
MoveNext( myCust ).
DEV-08, Exploring Object-oriented Programming

26. Benefits of Interfaces
Allows many different classes to be treated in a like manner
All classes that implement an interface are guaranteed to have same set of methods
Enables generic programming
IList example allows any collection of objects to be navigated using Next( )
Behavior can be specialized as needed
DEV-08, Exploring Object-oriented Programming

27. Summary : Object-oriented Constructs
Type
Enforces type consistency at compile time
Class
Defines type with data and methods and provides implementation
Object
Runtime instantiation of class
Interface
Defines type with methods – no implementation provided
DEV-08, Exploring Object-oriented Programming

28. Today’s Agenda Basic Principles of Object-oriented Programming
Types, Classes, Objects, and Interfaces
Inheritance, Polymorphism, and Delegation
DEV-08, Exploring Object-oriented Programming

29. Inheritance Super Class (Base class) Subclass (Derived class)
Relationship between Classes
Super Class
Super Class (Base class)
Provides common functionality and data members
Subclass (Derived class)
Inherits public and protected members from the super class
Can extend or change behavior of super class by overriding methods …
Subclass
DEV-08, Exploring Object-oriented Programming

30. Access Levels for Class Members
PRIVATE members available:
Only within the class
PROTECTED members available:
Within the class
Within the class hierarchy
PUBLIC members available:
To users outside the class
Order
PRIVATE
PROTECTED
PUBLIC
DEV-08, Exploring Object-oriented Programming

31. Inheritance Example Class: Order PRIVATE: orderNum AS INT
custNum AS INT
CalculateTotalPrice( )
PROTECTED:
GetCredit( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
DEV-08, Exploring Object-oriented Programming

32. Class InternalOrder inherits Order
Inheritance Example
Class InternalOrder inherits Order
Class: Order
PRIVATE:
orderNum AS INT
custNum AS INT
CalculateTotalPrice( )
InternalOrder
PROTECTED:
GetCredit( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
PROTECTED:
GetCredit( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
PROTECTED:
GetCredit( )
PUBLIC:
CreateOrder( )
UpdateOrder( )
GetOrderTotal( )
Next( )
DEV-08, Exploring Object-oriented Programming

33. Inheritance and Method Overriding
Method overriding used to specialize behavior
Subclass may override a method in its super class (hierarchy)
Method signatures must match
Overriden method can:
Completely override behavior of super class
Augment behavior by providing its own behavior and calling super class method
DEV-08, Exploring Object-oriented Programming

34. Method Overriding – Example 1
Order
PROTECTED:
GetCredit( )
credit = FindCreditScore( ).
Class InternalOrder inherits Order
InternalOrder
PROTECTED:
GetCredit ( )
credit = -1. /*unlimited*/
DEV-08, Exploring Object-oriented Programming

35. Method Overriding – Example 2
Order
PROTECTED:
GetCredit( )
credit = CalculateCredit( ).
Class ExternalOrder inherits Order
ExternalOrder
PROTECTED:
GetCredit( )
credit = SUPER:GetCredit( )
+ extraMoney.
DEV-08, Exploring Object-oriented Programming

36. Benefits of Inheritance and Overriding
Inheritance supports modular design
Common behavior put in super class and used by subclass
Subclass can override to specialize behavior
Inheritance is strongly-typed
InternalOrder myOrder = NEW InternalOrder.
myOrder.GetCredit( ).
myOrder knows it is an InternalOrder
DEV-08, Exploring Object-oriented Programming

37. Polymorphism
One interface, many implementations
Execution of an overridden method in a subclass from a reference to a super class
superclass:method( )
Code written using super class
Tightly coupled to inheritance and overriding
Super class used at compile time, subclass assigned at runtime
Method call on super class dispatched to subclass’ method at runtime
DEV-08, Exploring Object-oriented Programming

38. Polymorphism – Example
Order
PROTECTED:
GetCredit( )
credit = CalculateCredit( ).
InternalOrder
ExternalOrder
PROTECTED:
GetCredit ( )
credit = -1. /*unlimited*/
PROTECTED:
GetCredit( )
credit = SUPER:GetCredit( )
+ extraCreditPoints.
DEV-08, Exploring Object-oriented Programming

39. Polymorphism – Example continued
DEFINE myOrder AS Order.
if (bInternalCust = TRUE)
myOrder = NEW InternalOrder( ).
else
myOrder = NEW ExternalOrder( ).
myOrder:GetCredit( ).
Super Class reference
Calls InternalOrder:GetCredit( ) or ExternalOrder:GetCredit( )
DEV-08, Exploring Object-oriented Programming

40. Benefits of Polymorphism
Supports generic programming using super class or interface
Type used at compile time is super class or interface
Specialized behavior is called at runtime automatically
Built on inheritance and overriding
DEV-08, Exploring Object-oriented Programming

41. Delegation Delegation is the use of other objects within a class
Class forwards method calls to the contained object
Class wraps the delegate object
Creates an instance of the object
Defines a “stub” method for any referenced methods that should be public
No access to protected or private members
DEV-08, Exploring Object-oriented Programming

42. Class Order references a ShipInfo object
Delegation – Example
Class Order references a ShipInfo object
Order
PRIVATE:
ShipInfo shipObj
= NEW ShipInfo( )
PUBLIC:
GetShipDate( )
shipObj:GetDate( )
ShipInfo
PRIVATE: id
shipdate
promisedate
PUBLIC:
SetDate( ) GetDate( ) …
calls
DEV-08, Exploring Object-oriented Programming

43. Benefits of Delegation
Delegation supports modular design
Purposed class does work
Class uses delegate to provide needed functionality
Class can determine what to put in API
With inheritance super class dictates API; with delegation wrapper class decides what to expose
DEV-08, Exploring Object-oriented Programming

44. That’s Object-oriented Programming What did we learn…
DEV-08, Exploring Object-oriented Programming

45. Terminology / Concept Review
Abstraction – Public API
Encapsulation – Hide implementation details
Hierarchy – Relationships between classes
Strong-typing – Type consistency enforced
Class – Data members and methods
Object – Runtime instance of a class
Interface – Set of method definitions; contract
Inheritance – Inherit/specialize from super class
Polymorphism – Most-derived method called from super class reference
Delegation – Other objects do the work
DEV-08, Exploring Object-oriented Programming

46. Benefits of OO Programming
Promotes modular design
Data and methods that operate on that data are contained in one place
Commonalities put into super classes
Code reuse through hierarchies
Inheritance and delegation
Strong-typing
Compile-time type checking
Runtime type checking
DEV-08, Exploring Object-oriented Programming

47. Recommended OO Books
Object-Oriented Analysis and Design with Applications (2nd Edition) by Grady Booch
Object-Oriented Modeling and Design by James R Rumbaugh…
Design Patterns, Elements of Reusable Object-oriented Software by Erich Gamma…
DEV-08, Exploring Object-oriented Programming

48. **Attend Session DEV-10 for details
In Summary
Object-oriented programming is more than syntax – must be part of design
Many benefits in OO Programming
Can be combined with procedural programming, not all or nothing
OpenEdge™ 10.1 Language enhancements support object-oriented programming naturally
**Attend Session DEV-10 for details
DEV-08, Exploring Object-oriented Programming

49. Questions?
DEV-08, Exploring Object-oriented Programming

50. Thank you for your time!
DEV-08, Exploring Object-oriented Programming

51. DEV-08, Exploring Object-oriented Programming