1. INFO 16029 - Problem Solving & Programming Logic
4/15/2017
Inheritance
Wendi Jollymore, ACES

2. INFO 16029 - Problem Solving & Programming Logic
4/15/2017
What is Inheritance?
A type of relationship between classes.
There are a few different kinds of class relationships
Inheritance is also called Generalization
Occurs when one specific class “inherits” the characteristics and behaviors of a more general class
It’s easier to understand with examples 
4/15/2017
Wendi Jollymore, ACES
Wendi Jollymore, ACES

3. What is Inheritance? Which of these are valid/true assertions?
All cars are vehicles
All airplanes are vehicles
All vehicles are cars
We can say that:
A car is a type of vehicle
A bike is a type of vehicle
A UFO is a type of vehicle
True
False
4/15/2017
Wendi Jollymore, ACES

4. What is Inheritance?
We often say that Inheritance is an “is a” relationship
A car is a vehicle
A bike is a vehicle
A fork is a utensil
A cat is a feline
One term is more general, the other more specific
Vehicle, Utensil, Feline are general
Car, bike, fork, cat, are specific
4/15/2017
Wendi Jollymore, ACES

5. What is Inheritance?
What characteristics and behaviors to all vehicles share?
Characteristics:
Colour, number of wheels, number of passengers, brand or model
Behaviors:
Start, stop, accelerate/decelerate
4/15/2017
Wendi Jollymore, ACES

6. What is Inheritance?
What characteristics/behaviors are different between a car and an airplane?
Airplanes can fly
Cars can reverse
4/15/2017
Wendi Jollymore, ACES

7. What is Inheritance
In programming, the more general class is called the parent class or super class
The more specific classes are called child classes or sub classes.
Parent
Class
Child
In Java, a child class is only allowed one parent class…
…however, a parent can have many child classes
4/15/2017
Wendi Jollymore, ACES

8. What is Inheritance Examples Vehicles Car Airplane Bicycle Utensils
Fork
Spoon
Knife
Examples
Vehicles
Car
Airplane
Bicycle
4/15/2017
Wendi Jollymore, ACES

9. What is Inheritance?
A child class contains the characteristics and behaviors of its parent
It might also have characteristics and behaviors of its own
It might also have the same behaviors as the parent, but they just work differently
Example: You can drive a car and drive a plane, but not the same way
4/15/2017
Wendi Jollymore, ACES

10. Example Full time employees Part time employees work 40 hours per week
get paid an annual salary
weekly pay = annual salary / number of full weeks they work
Part time employees
can work a varying number of hours per week
weekly pay = #of hours worked * hourly rate.
4/15/2017
Wendi Jollymore, ACES

11. Example Sales employees Temporary sales employees have varying hours
weekly pay = commission amount = a percentage of their weekly sales
they also get a flat lump sum or base pay per week
Temporary sales employees
just like regular sales employees except that they don't get the base pay each week, just commissions
4/15/2017
Wendi Jollymore, ACES

12. Example
In a payroll program, what data would we need to know about all employees?
First name, last name, sin, employee id, address, phone number, city, province, postal code, etc.
Data used to calculate pay for employees depends on the type of employee!
4/15/2017
Wendi Jollymore, ACES

13. Example Full time employees: Part time employees Sales employees
annual salary, weeks worked
Part time employees
hours worked, hourly rate
Sales employees
weekly sales, commission rate, base pay.
Temporary sales employees
weekly sales, commission rate.
4/15/2017
Wendi Jollymore, ACES

14. Example
Writing each of the 4 classes with all of the data and methods would be tedious!
We usually take the common things and put them in a parent class
Then the child classes contain all the “extras”
And modify parent methods, if needed
4/15/2017
Wendi Jollymore, ACES

15. Example Employee Class: Employee Data Members:
first name last name employee id sin phone number address city province postal code
Methods:
calculateWeeklyPay()
printCheck()
4/15/2017
Wendi Jollymore, ACES

16. Example Child Classes: FullTimeEmployee extends Employee Data Members:
annual salary
weeks worked
Methods:
calculateWeeklyPay()
PartTimeEmployee extends Employee
Data Members:
rate of pay
hours worked
Methods:
calculateWeeklyPay()
4/15/2017
Wendi Jollymore, ACES

17. Example
Note that SalesEmployee and TempSalesEmployee are very similar:
SalesEmployee
extends Employee
Data Members:
commission rate
weekly sales
base pay
Methods:
calculateWeeklyPay()
TempSalesEmployee
extends Employee
Data Members:
commission rate
weekly sales
Methods:
calculateWeeklyPay()
4/15/2017
Wendi Jollymore, ACES

18. Example We could make Sales Employee a child class of Sales Employee
TempSalesEmployee
extends Employee
Data Members:
commission rate
weekly sales
Methods:
calculateWeeklyPay()
SalesEmployee
extends TempSalesEmployee
Data Members:
base pay
Methods:
calculateWeeklyPay()
4/15/2017
Wendi Jollymore, ACES

19. Example
4/15/2017
Wendi Jollymore, ACES

20. One More Example Vessels have a length characteristic and can steer().
Sailboats and Destroyers are Vessels
both have length and can steer().
Sailboats have sails and can raiseJib(), but not all vessels have these.
Destroyers have deckPlating and can fireGuns(), but not all vessels have these.
What would a hierarchy chart look like with the classes Vessel, Sailboat, and Destroyer?
4/15/2017
Wendi Jollymore, ACES

21. Possible Solution
4/15/2017
Wendi Jollymore, ACES

22. Exercise
For each of the following, which classes would be parent classes, which would be child classes?
Draw the hierarchy charts!
Loafer, Sneaker, Shoe, Sandal
Checking Account, Bank Account, Savings Account
Cat, Cow, Feline, Animal, Chicken, Bovine, Avian, Tiger, Yak, Parrot
4/15/2017
Wendi Jollymore, ACES

23. Robots and Inheritance
Look up the RobotSE class in the documentation
(class discussion)
4/15/2017
Wendi Jollymore, ACES

24. Creating Your Own Robot
You can use Inheritance to create your own Robot
You can give it your own methods like faceDirection() and makeBox()
How about a collectThings() method that gives the robot a certain number of coloured things?
We’ll do this in class
4/15/2017
Wendi Jollymore, ACES