Review of OOP Terms

• We are currently focused on classes.
  • Classes are the foundation of object oriented programming.
  • Classes are the C++ way to implement an object.
• What is an object?
  • An object is a entity that has state, behavior and identity. (Object Oriented Analysis and Design.)
  • An object is a run-time instance of a class. (Object Oriented Software Construction)
  • Our book fails to define object.
  • In a real sense, an object is a "thing" that we wish to use in a program.
    • It contains a state
      • The condition of the object.
      • These are the variables.
    • It contains a set of actions that can be performed
      • The things you can do with/to the item we are modeling.
      • These are the methods or functions.
    • Finally it exists
      • Probably electronically
  • Some things are not objects.
    • Selection sort is not an object
      • It does not have data.
      • It is just an algorithm
    • red is not an object
      • it is just a data value.
      • There are no operations on red.
  • Don't go too deep here.
  • So a class in c++ is the programming construct that can be used to represent an abstract data type.
  • And an abstract data type is ... A data type whose properties (domain and operations) are specified independently of any particular implementation.
  • Classes are composed of members which define the properties
    • A member is a component of a class
    • There can be member functions (the operations)
    • There can be member data (the domain)
  • A class instance is a variable of the class type.
    • The class definition is a prototype, template or plan
    • This tells the compiler how to create an instance of the class.
    • By declaring an instance of the class we build an object.
      • The class constructor is invoked to assign the state.
  • A client is the software that declares and manipulates objects of a class.
    • Note that we have moved away from the final user of the software.
  • Syntax

    • class identifier {
           accessModifier:
               MemberList;
           accessModifier:
               MemberList;
               ...
      };
              

    • The access modifier are
      • public members are available to client code.
      • private members are only available to class instances.
      • This is somewhat false, but will do until next semester.
    • Informally a MemberList consists of
      • Variable definitions
      • Function Prototypes
      • Again, there can be more here, but this will do until next semester.
  • Classes have five different types of member functions
    • Constructors
    • Destructors
    • Observers (getters)
    • Transformers (setters)
    • Iterators
  • Class Scope
    • Members of a class are in scope or visible to all other members
    • And all other instances of the class.
  • The book discusses a few topics that we have hit on informally in the past.
  • Information Hiding
    • The encapsulation and hiding of implementation details to keep the user of an abstraction from depending on or incorrectly manipulating these details.
    • How is this related to an ADT?
    • How do we practice information hiding in c++?
      • The private section of a class.
      • Placing header and code in different files.
    • Why do we practice information hiding?
  • Encapsulation?
    • Designing a class so that its attributes are isolated from the actions of external code except through the formal interface (book)
    • The bundling of data and methods. (a more generic term)
    • Encapsulation is the process of compartmentalizing the elements of an abstraction that constitute its structure and behavior. (OO Analysis and Design)
    • Encapsulation is sometimes used as a synonym for information hiding (OO Software Construction)
    • In general, I prefer the second one, but add that this is to facilitate information hiding.