[PL]Ch. 10 - Object-Oriented Programming(OOP)

. Object-oriented programming
  . Primary object-oriented language concepts
  . Dynamic lookup
  . encapsulation
  . inheritance
  . subtyping
  . Program organization
  . Work queue, geometry program, design patterns
  . Comparison
  . Objects as closures?

. Objects
  . An object consists of
  . hidden data
     . instance variables, also called member data
     . hidden functions also possible
  . public operations
     . methods or member functions can also have public variables in some languages

  . Object-oriented program
  . send messages to objects

. What's interesing about this?
  . Universal encapsulation construct
  . Data structure
  . File system
  . Database
  . window
  . Integer

  . Metaphor usefully ambiguous
  . sequential or concurrent computation
  . distributed, sync. or async. communication

. Object-Orientation
  . Programming methodology
  . orginize concepts into objects and classes
  . build extensible systems

  . Language concepts
  . Dynamic lookup
  . Encapsulation
  . Subtyping allows extensions of concepts
  . Inheritance allows reuse of implementation

. Dynamic Lookup
  . In object-oriented programming, object message(arguments)
  code depends on object and message

  . In conventional programming, operation (operands)
  meaning of operation is always the same

  . Fundamental difference between abstract data types and objects

. Example
  . Add two numbers
  . different add if x is integer, complex

  . Conventional programming add(x,y)
  . function add has fixed meaning

  . Very important distinction:
  . Overloading is resolved at compile time, Dynamic lookup at run time.

. Encapsulation
  . Builder of a concept has detailed view
  . User of a concept has abstract view
  . Encapsulation separates these two views
  . Impelmentation code : operate on representation
  . Client code : operate by applying fixed set of operations provided by implementer of abstraction

. Languge concepts
  . "Dynamic lookup"
  . Different code for different object
  . Integer "+" different from real "+"
  . Encapsulation
  . subtyping
  . Inheritance

. Subtyping and Inheritance
  . Interface : The external view of an object
  . Subtyping : Relation between interfaces
  . Implementation : The internal representation of an object
  . Inheritance : Relation between implementations

. Object Interfaces
  . Interface : The messages understood by an object
  . The interface of an object is its type

. Subtyping
  . If interface A contains all of interface B, then
  A objects can also be used B objects.
  . Colored_point interface contains Point
  . Colored_point is a subtype of Point

. Inheritance
  . Implementation mechanism
  . New objects may be defined by reusing implementations of other objects

. Subtyping
  . Colored points can be used in place of points
  . Property used by client program

. Inheritance
  . Colored points can be implementated by reusing point implementation
  . Technique used by implementer of classes

. OO Program Structure
  . Group data and functions
  . Class : Defines behavior of all objects that are instances of the class
  . Subtyping : Place similar data in related classes
  . Inheritance : Avoid reimplementing functions that are already defined
  . Subtyping differs from inheritance

. Design Patterns
  . Classes and objects are useful organizing concepts
  . Culture of design patterns has developed around object-oriented programming
  . Shows value of OOP for program organization and problem solving

. What is a design pattern?
  . General solution that has developed from repeatedly addressing similar problems
  . ex) singleton
  . restrict programs so that only one instance of a class can be created
  . signleton desing pattern provides standard solution
  . Not a class template
  . Using most patterns will require some thought
  . Pattern is meant to capture experience in useful form

. Varieties of OO languages
  . class-based languages (C++, Java, ...)
  . behavior of object determined by its class
  . object-based (Self)
  . objects defined directly
  . multi-methods (CLOS)
  . operation depends on all operands

. History
  . Simula : Object concept used in simulation (1960's)
  . Smalltalk : Object-oriented design, systems (1970's)
  . C++ : Adapted Simula ideas to C (1980's)
  . Java : Distributed programming, internet

. Summary
  . Object-oriented design
  . Primary object-oriented language concepts
  . dynamic lookup
  . encapsulation
  . inheritance
  . subtyping
  . Program organization
  . Work queue, geometry program, design patterns
  . Comparison
  . Objects as closures