Æliens

• abstraction -- the object metaphor
• modeling -- understanding structure and behavior
• software architecture -- mastering complexity
• frameworks -- patterns for problem solving
• components -- scalable software

Object terminology

object speak

• objects -- packet containing data and procedures
• methods -- deliver service
• message -- request to execute a method
• class -- template for creating objects
• instance -- an object that belongs to a class
• encapsulation -- information hiding supported by objects
• inheritance -- mechanism allowing the reuse of class specifications
• class hierarchy -- tree structure representing inheritance relations
• polymorphism -- to hide different implementations behind a common interface

• information hiding -- state, autonomous behavior
• data abstraction -- emphasis on what rather than how
• dynamic binding -- binding at runtime, polymorphism
• inheritance -- incremental changes (specialization), reusability

OO = encapsulation + inheritance

benefits of OOP

• modularity -- autonomous entities, cooperation through exchanges of messages
• deferred commitment -- the internal workings of an object can be redefined without changing other parts of the system
• reusability -- refining classes through inheritance
• naturalness -- object-oriented analysis / design, modeling

the object model

• computation is sending messages between objects

message

• object method arguments

encapsulation

• objects encapsulate data and procedures

protocol

• the collection of messages an object supports

Computing devices

• mathematical model -- Turing machine
• universal machine -- machines as programs
• computability \& complexity -- time/space bounded

Object-oriented programming does not enlarge the class of computable problems, nor does it reduce the computational complexity of the problems we can handle.

Encapsulation

• abstract data types

Object-oriented modeling

• data oriented

• to specify behavior

  what rather than how

client/server model

• makes request to perform a service

• provides service upon request

Contracts

• a set of services

• improving contracts

Conformance -- behavioral refinement

Object-oriented modeling

• prototyping, specification, refinement, interactions