1.
OBJECTS AND CLASSES
Martin Chapman
martin.chapman@kcl.ac.uk

2.
•Fundamental principle:
•The difference between blueprints and
buildings

3.
•Fundamental principle:
•The difference between blueprints and
buildings
data type
variable
variable

4.
•Fundamental principle:
•The difference between blueprints and
buildings
int
num1 = 9
num2 = 20

5.
•Fundamental principle:
•The difference between blueprints and
buildings
class
object
object

6.
•There are two predominant ways to understand
Object Orientation:
•Understand how we do it.
•Understand why we do it.

7.
How do we do it?

8.
class
object

9.
class
object

10.
class
object

11.
class
object

12.
class
object

13.
1. Make a class with methods and variables
2. Make an object (a variable) to link to that class
3. Reference the object to use the methods you
made in Step 1.

14.
1. Make a class with methods and variables
2. Make an object (a variable) to link to that class
3. Reference the object to use the methods you
made in Step 1.

15.
Among other reasons...
•It makes sense
•Code reuse
•State and behaviour
•It gives us control
•Constructors
•Encapsulation

16.
Among other reasons...
•It makes sense
•Code reuse
•State and behaviour
•It gives us control
•Constructors
•Encapsulation

17.
Dave
Victoria

18.
Codereuse

19.
Codereuse

20.
Codereuse

21.
davesCar victoriasCar
Codereuse

22.
blue
davesCar victoriasCar
Codereuse

23.
blue black
davesCar victoriasCar
Codereuse

24.
Codereuse

25.
blue black
davesCar victoriasCar
Codereuse

26.
Among other reasons...
•It makes sense
•Code reuse
•State and behaviour
•It gives us control
•Constructors
•Encapsulation

27.
Drive Colour
Speed
Number of wheels
Number
plate
Height
Stateandbehaviour
Paint

28.
•All the information we want our program to have
about this object can be categorised as:
•“How the object is” (~Nouns / Adjectives).
•Colour, numberplate, speed and number of
wheels etc.
•“What can be done to the object” / “What the
object can do” (~Verbs).
•Drive and be painted
Stateandbehaviour

29.
•All the information we want our program to have
about this object can be categorised as:
•“How the object is”.
•Colour, numberplate, speed and number of
wheels etc.
•“What can be done to the object” / “What the
object can do”.
•Drive and be painted
STATE
BEHAVIOUR
Stateandbehaviour

30.
STATE
BEHAVIOUR
BEHAVIOUR
BEHAVIOUR
BEHAVIOUR
Stateandbehaviour

31.
VARIABLES
METHOD
METHOD
METHOD
METHOD
Stateandbehaviour
Behaviour
Behaviour
Behaviour
Behaviour
State

32.
FIELDS
METHOD
METHOD
METHOD
METHOD
Stateandbehaviour
StateVariables
(Properties)

33.
Among other reasons...
•It makes sense
•Code reuse
•State and behaviour
•It gives us control
•Constructors
•Encapsulation

34.
CONSTRUCTOR
A method which has the
same name as the class
is called an explicit
Constructors

35.
Constructors

36.
Constructors

37.
Constructors

38.
Among other reasons...
•It makes sense
•Code reuse
•State and behaviour
•It gives us control
•Constructors
•Encapsulation

39.
Encapsulation
Private
Public
Only visible
inside
the class
Visible
anywhere

40.
Encapsulation

41.
Encapsulation

42.
Encapsulation
Interface

43.
Encapsulation

44.
Encapsulation

45.
• Object orientation, in its simplest form, is code within
code.
• By programming in an OO manner, we are designing code in a
way that both makes sense and gives us control.
• OOP makes sense because it allows for efficient reuse
and an accurate representation of the world using state
and behaviour.
• OOP gives us control through constructors and because it
enforces encapsulation (a black-box approach to
object design in which operations are performed through
well-defined method interfaces).
SUMMARY