Chapter 12, Classes and Abstraction

• We begin to move from procedural programming to object oriented programming.
• What is functional decomposition?
• Notice that this focuses on functions
• Abstract data type (ADT): A data type whose properties (domain and operations) are specified independently of any particular implementation.
  • What are the domain of a data type?
  • What are the operations on a data type?
  • Think about strings:
    • Answer the two above questions.
• Note, when we discuss functions, we discuss only flow of control
  • With perhaps a hint of data (parameters) thrown in.
• The definition of ADT changes that.
• This is a new way to think about things and it IS different from what you have learned so far.
• From early times until the early 70's everything was functional decomposition/procedural programming
  • Early OO languages were adopted in the 70s
  • Stroustrap released c++ in 85.
• There is still an incredibly large base of procedural code out there.
• Just a side note, c++ is not an object oriented language. It is Multi-paradigm
  • procedural
  • imperative
  • functional
  • object-oriented
  • generic
  • modular
• Building an ADT in C++
  • The class construct is the way objects/ADTs are built in c++
  • You will eventually discover that classes and structs are essentially the same thing.
  • But we tend to use structs as collections of data, a procedural programming idea.
  • We uses classes to implement ADT's.
• Classes have
  • member data, the data associated with an object.
  • member function, the functions needed to manipulate and observe that data.
  • Protection: the ability to keep "programmers" from changing the data in unexpected ways.
• Basic Syntax

  • class identifier {
       access modifier:
          member list
       access modifier:
          member list
    }; 

  • Access modifiers consist of
    • private only instances of the class can access members listed here.
    • public any code can access this method.
  • member lists consist of
    • variable declarations, with initialization if desired (since c++11)
    • function declarations
• Unless marked otherwise, all members are private.
  • This is the only syntatic/semantic difference between a class and a struct.
  • Structs - everything is public.
  • Structs may have function and access modifiers.
• Instances of a class are called objects
• There are a set of standard member functions
  • A constructor initializes the object.
  • A destructor cleans up after an object when it is destroyed.
  • A observer or getter examines an object.
  • A transformer or setter changes an object.
• The methods or function members of a class determine the formal interface.
  • You need to provide sufficient methods to fully manipulate an instance of a class.
• There is much more, but this is enough for a start.