CPS120: Introduction to Computer Science

1
CPS120 Introduction to Computer Science

• Lecture 16A
• Object-Oriented Concepts

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The Procedural Paradigm

• The functions and algorithms are the focus, with
  data viewed as something for the functions to
  manipulate

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Object-Oriented Paradigm

• Data should be placed inside the objects and that
  these objects should communicate with each other
  in the form of messages

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OOP

• Object-oriented programming (OOP) is the process
  of developing programs using the object-oriented
  paradigm

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Classes

• The definition of an object is know as a class
• It is similar to using basic data structures in
  C
• When you declare an object, you are said to have
  instantiated it (given it instances)
• Objects are members of a class
• Paul Millis, George Bush and George Washington
  being members of the human being class
• The design of a class is as important as its
  implementation

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Including Classes in C

• For classes, the include directive uses
  different punctuation for header (.h) files
• Quotation marks are used when the header file is
  a source file in the same location as the program
  source code
• Angle brackets are used when the header file is
  one of the compiler's pre-compiled library
  functions

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Using Header Files for Classes

• Header files normally contain declarations of
  variables, functions and classes, but not
  implementations of the functions and classes

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Designing a Class

• Think in an object-oriented way
• E.g. an answering machine encapsulates the
  functions of an answering machine with the data
  (messages).
• The buttons are the equivalent of sending
  messages to the machine

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Defining a Class

• Functions and variables that are prototyped and
  declared in a class definition are called members

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Public vs Private

• Private cannot be accessed outside the object
• Public Can have access to all the variables and
  functions

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Constructors

• Allow all data encapsulated within an object to
  be initialized to preset values so that errors
  can be avoided

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Member Functions

• Provide a way for a programmer to pass data to
  and get data from an object
• Implemented like a normal C function
• Except -- The class name and the scope-resolution
  operator ( ) precede the function name
• circle circle() // default constructor

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OOP Advantages Reusability

• Reusability is a major benefit of object-oriented
  programming

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OOP Advantages Containment

• Containment is a term used to describe an object
  that contains one or more objects as members
• (Passes the 'has-a' rule)

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OOP Advantages Inheritance

• Inheritance is the term used to describe an
  object that inherits properties from another
  object
• (Passes the 'is-a' rule)
• The class from which an object inherits
  properties is called a parent class or base class
• The class that inherits the properties is called
  a child class or derived class

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Multi-level Inheritance

• Inheritance can be multi-level (i.e. from
  grandparents)

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Multiple Inheritance

• Objects can inherit properties form multiple
  objects
• Multiple inheritance should be used sparingly