• to understand why we need object-oriented techniques
• to introduce object-orientation concept

• Evolution in programming
• why do system fail
• basic ideas of object-orientatiom
• what is object-oriented programming
• classes and objects
• abstraction
• encapsulation
• Instantiation
• Ploymorphism
• Inheritance

Handcrafted programming

• pre-compiler era, mostly machine code
• more of an art than science

• concept of subroutines
• complex logic is broken down into maintanable fragments
• require a lot of dicipline

• functional decomposition
• top-down approach in programming design
• consists of multiple levels of subroutines
• emphasis on team-work of development
• costly to change/maintain

• Dynamic bussiness requirements
• Complex modern information structure
• Open, heregenous environment
• Cost
• Time

• accurately model (changing) bussiness requirements
• highly scalable
• promote reusability
• hide complexity
• ease of maintanance/change
• increase productivity

• The world is full of things

 
• we abstract things and call the abstraction objects
• we talk to object, not their parts
• object can be
• tangible


 
 

• intangible
• ex:
• cheque
• schedule
• flight

• A method of implementation in which programs are organized as cooperative collections of objects, each of which represents an instance of some class, and whose classes are all members of a hierarchy of classes united via inheritance relationship.

• Classes and Objects
• Abstraction
• Encapsulation
• Instantiation
• Polymorphism
• Inheritance

• An object has state, behavior and identity

• Property of an object which distinguishes it from other objects

• The state of an object is held in object values
• The object changes state whenever any of its variables change value

• How an object acts and reacts in terms of its state changes and message passing
 

• Description of set of objects with similar properties
• A set of objects that share a common structure and a common behavior

Class name and its interface

Messages

• sent to receiver object
• message-send always returns an object
• a message may include parameters
• only way to communicate with an object

• Has a name that is the same as message name
• Determine how the object acts upon receiving the message
• Is a sequence of executable statement
• Returns an objects as its result of execution
• Similar to a function call in traditional programming

• The process of focusing on the essential, inherent aspects of an entity and ignore its accidental. (Focus on what an objet does before deciding how it should be implemented)

• The process of hiding all of the details of an object that do not contribute to its essential characteristics.
• The warapping up of  data and functions into a single unit(class)
• The data is not accessible to the outside world and only functions which are wrapped in the class can access it (information hiding)

• A creation of an instance of a class
• Only one class needs to be defined for one or more creation of class object instances
• Each instance is unique
• Each instance has its own value for each attribute but share the attribute names and operations with other instances of the class.

• The ability to take more than one form
• An operation may exhibit different behaviour in different instances

• An operation may exhibit different behaviour in one instance based on the argument send to it.
• Example:
• Fly();
• Fly(200,50);
• Fly(150);
 

• The sharing of attribute and operations among classes based on a hierarchical relationship
• A class can be defined broadly and then refined into succesively finer subclass
• Subclasses
• Inherits all of the properties of its superclasses and adds its own unique properties
• Encourage reuse

• Abstract class
• Holds on to common behaviour and characteristics
• Not expected to have instances
• Concrete class
• Contains complete description of actual objects
• Expected to be instantiated