← VCE Software Development U3O1

OOP principle: abstraction

Modelling only the attributes and methods that matter for a purpose and hiding the rest of the detail, such as a Student class that keeps just the data a school app needs.

Part of: VCE Software Development - U3O1 - Programming — Module 137, VCE Software Development - U4O1 - development and evaluation — Module 83

Understanding OOP principle: abstraction in VCE Software Development U3O1

What it does: A library Member holds name and cardNo only. A hospital Patient model of the same person would hold different attributes, showing same real thing, different abstractions. Callers use calculate_total() without needing to know how the total is worked out, which hides complex detail behind a method. Abstraction keeps what is relevant to the purpose and leaves out the rest. A school app needs school-related data. Attributes like shoe size are irrelevant to its purpose, so they are left out. An ISBN helps identify and borrow books. The paper weight is unnecessary detail for a library app. Hiding the working inside a method lets the caller focus on what it does, not how.

Common mistakes: Every method in a class needs self as its first parameter. The Student class keeps only the name a school app needs and hides the rest behind show(). It should be def show(self):. The constructor needs double underscores on both sides. The Book class models just the title a library search needs. It should be def __init__(self, title):.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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Learning
Duo
Which best describes abstraction in OOP?
Including every possible detail about a real-world thing in a classModelling only the attributes and methods that matter for the purpose
Matches
class Student: def __init__(self, name, eyeColour, pet, shoeSize, year):
↓
The class includes irrelevant attributes (eyeColour, pet, shoeSize) for a school app. Abstraction means keeping only the attributes that matter for the purpose, such as name and year.
Applying
Meanings
Term
abstraction
Meaning
Modelling only the attributes and methods that matter for a purpose and hiding the rest of the detail, such as a Student class that keeps just the data a school app needs.
Practice
class Student:
Testing
Gaps
Student:
Check Answer
Spots
3 self.name = name
4 def show():

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Quick Questions

1. Which best describes abstraction in OOP?
A. Including every possible detail about a real-world thing in a class
B. Modelling only the attributes and methods that matter for the purpose ✓
Abstraction keeps what is relevant to the purpose and leaves out the rest.
2. A school app has a Student class. Which attributes are the better abstraction?
A. studentId, firstName, yearLevel, house ✓
B. shoeSize, favouriteColour, petName, bloodType
A school app needs school-related data. Attributes like shoe size are irrelevant to its purpose, so they are left out.
3. What does a method like car.start() show about abstraction?
A. It hides complex detail (fuel, spark, engine) behind one simple method call ✓
B. It forces the user to write code for every engine part
The caller uses start() without needing to know how it works inside.
4. A game and a bank both model a Person class. Which statement is true?
A. Both must include exactly the same attributes, because it is the same real person
B. Each can use a different abstraction of Person, because their purposes differ ✓
The same real thing can be modelled differently. A game might store score and level, while a bank stores accountNumber and balance.
5. A Library app models a Book. Which attribute is relevant to the purpose?
A. isbn ✓
B. paperWeightInGrams
An ISBN helps identify and borrow books. The paper weight is unnecessary detail for a library app.

Match the Pairs

class Student: def __init__(self, name, year): → Abstraction: the Student class keeps only the attributes a school app needs (name, year level) and leaves out details like eye colour or favourite food.
account.deposit(50) → Abstraction: the deposit() method hides the complex steps (checking, updating, logging) so the caller just asks for the result.
Abstraction: the same real thing (a person) can be modelled with different attributes for different purposes, such as a library app. → class Member: def __init__(self, name, cardNo):
Abstraction: a method hides how a task is done so other code only needs to know what it does. → def calculate_total(self): return sum(self._prices)
class Student: def __init__(self, name, eyeColour, pet, shoeSize, year): → The class includes irrelevant attributes (eyeColour, pet, shoeSize) for a school app. Abstraction means keeping only the attributes that matter for the purpose, such as name and year.
total = 0 for p in cart._prices: total += p print(total) → The calling code repeats the detail of how the total is calculated instead of using a method like cart.calculate_total() that hides it.

Key Term

abstraction
Modelling only the attributes and methods that matter for a purpose and hiding the rest of the detail, such as a Student class that keeps just the data a school app needs.

Fill in the Blanks

1. class Student: def show(self): return self.name
Hint: Type the keyword that starts a class definition, the blueprint that models only the details a school app needs.
2. class Car: def start(self): self.check()
Hint: Type the keyword that defines a method, a simple action that hides the complex engine checks behind it.
3. class Kettle: def boil(self): self.heat()
Hint: Type the name that refers to the current object, so the method can call its own hidden helper.
4. class Patient: def info(self): return self.allergy
Hint: Type the keyword that sends the stored medical detail back to the code that called the method.
5. def area(w, h): return w * h print(area(3, 4))
Hint: Type the name of the function being called, which hides the calculation behind a simple call.

Spot the Error

Question 1
A class Student:
B def __init__(self, name):
C self.name = name
D def show():
E print(self.name)
Line D — Every method in a class needs self as its first parameter. The Student class keeps only the name a school app needs and hides the rest behind show(). It should be def show(self):
Question 2
A class Book:
B def _init_(self, title):
C self.title = title
D b = Book("Dune")
E print(b.title)
Line B — The constructor needs double underscores on both sides. The Book class models just the title a library search needs. It should be def __init__(self, title):
Question 3
A class Car:
B def start(self):
C print("Engine on"
D my_car = Car()
E my_car.start()
Line C — The print call is missing its closing bracket. A driver only calls start() and the engine detail stays hidden inside the method. It should be print("Engine on")
Question 4
A class BusStop:
B def __init__(self, name):
C name = name
D def show(self):
E print(self.name)
Line C — This only sets a local variable, so the object never stores the attribute. A bus app keeps just the stop name, so it should be self.name = name
Question 5
A class City:
B def __init__(self, name):
C self.name = name
D self.roads == []
E c = City("Perth")
Line D — A double equals compares values. It does not assign them. A map app models a city by its roads (a tourism app would keep different details). It should be self.roads = []

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