Inheritance
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Inheritance. 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

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Inheritance

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Inheritance

Inheritance


What is inheritance

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 

Wendi Jollymore, ACES


What is inheritance1

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

Wendi Jollymore, ACES


What is inheritance2

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

Wendi Jollymore, ACES


What is inheritance3

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

Wendi Jollymore, ACES


What is inheritance4

What is Inheritance?

  • What characteristics/behaviors are different between a car and an airplane?

    • Airplanes can fly

    • Cars can reverse

Wendi Jollymore, ACES


What is inheritance5

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.

In Java, a child class is only allowed one parent class…

…however, a parent can have many child classes

Wendi Jollymore, ACES


What is inheritance6

What is Inheritance

  • Examples

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What is inheritance7

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

Wendi Jollymore, ACES


Example

Example

  • Full 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.

Wendi Jollymore, ACES


Example1

Example

  • 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

Wendi Jollymore, ACES


Example2

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!

Wendi Jollymore, ACES


Example3

Example

  • Full time 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.

Wendi Jollymore, ACES


Example4

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

Wendi Jollymore, ACES


Example5

Example

  • Employee Class:

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Example6

Example

  • Child Classes:

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Example7

Example

  • Note that SalesEmployee and TempSalesEmployee are very similar:

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Example8

Example

  • We could make Sales Employee a child class of Sales Employee

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Example9

Example

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One more example

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?

Wendi Jollymore, ACES


Possible solution

Possible Solution

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Exercise

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

Wendi Jollymore, ACES


Robots and inheritance

Robots and Inheritance

  • Look up the RobotSE class in the documentation

    • (class discussion)

Wendi Jollymore, ACES


Creating your own robot

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

Wendi Jollymore, ACES


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