Objects and Classes

1
Objects and Classes

• A very brief first introduction

2
Objects

• Things we deal with every day are examples of
  objects.
• My_car is an object. It is a burgundy,91,
  Buick, owner Lackey
• Your_car is an object. It is a ______, ____,
  ____, _______.
• My_car and Your_car are just two members of a
  much larger collection of All_Cars.
• This much larger collection is called a Class.

3

• In our discussion the class All_Cars is described
  by color, year, make, and owner.
• There are some operations or functions associate
  with All_Cars that may be useful such as
• changeOwnerName
• changeCarColor

4
Class

• A class defines the types of data we are dealing
  with that are of interest to us. In this case
• Color
• Year
• Make
• Owner
• and a class defines the type of things we can do
  with the data like changeCarColor, ..

5
Example 2

• Your Banner student record is an object. It has
  your name, address, e-mail, courses taken,
  courses you are taking, grades, etc.
• This is one instance or object in the much larger
  class of LTU_Banner_Students.

6
Describing LTU_Banner_Students

• Data.
• Name
• Address
• E-mail
• Courses_taken
• Current_courses
• Etc.
• Thing we can do to the data.
• changeEmail
• dropClass
• many others

7
Question about the class LTU_Banner_Students

• Is eye color an important characteristic use by
  the University to describe a student?
• Ans NO
• It is not meaningful in the Universitys
  application. It is an attribute or characteristic
  that may be important in some other application,
  but not in Banner.

8
Example 3from C

• objects or things
• 2
• 3
• int x
• things we can do with the data
• max(x,31)

9

• The class is called integers.
• The things we can do.
• /
• -
• Etc.
• When a C program contains int x is defining
  the object x which is one member of the class int
  and allows us to do things like or max or .

10
Object

• An object is one member (or instance) of a
  defined class. An object is a software collection
  of related variables (data) and functions (or
  operations) that can act on those variables.

11
Example of a software circle class and object

• Example A class called Circle.
• Data describing all circles.
• radius (we will use variable r)
• Functions
• area(r) .. (which is ? rr)
• distanceAround(r) .. (2?r)

12
Using the Circle class

• void main (void)
• double y 2.77
• Circle sample1 // creates an object like
  saying int x
• Circle sample2 // creates another object
• coutltlt sample1.area(y)ltltendl
• coutltlt sample2.distanceAround(2y)
• getchar() return

13
Class

• A Class is a template for and object. The
  definitions of data and functions that act on the
  data are contained in a class. It is a prototype
  that defines the variables and the functions
  common to all objects belonging to the class.
• An object is an instance of a class.