3 - Programming Paradigms/OOP

A-Level AQA Computer Science

What is a programming paradigm?

A programming paradigm is a fundamental style of writing computer code, which contains a framework for how data should be organised/designed.

What does ‘Turing complete’ mean?

When a language can solve all problems a computer can.

What is the order of low level languages?

Hardware → Machine Learning → Assembly

What is the difference between ML and assembly?

ML: Binary, closest to what happens on a computer

Assembly: Mnemonics

What do high-level languages involve?

One instruction = Many lines of code

More complex

Similar to human speech

What are the two types of high-level languages?

Imperative

• Uses statements to change a program’s state via sequence, selection, and iteration.

• Sub-divided into procedural (built on subroutines) and object-oriented (more modular)

Declarative:

• Focuses on what the program should achieve.

What are the characteristics of OOP and procedural programing?

Procedural:

• Seq, selection, iteration

• Stored in variables

• Subroutines

• Expressed in procedure calls

OOP:

• Seq, selec, iteration, inheritance, encapsulation, etc…

• Stored in attributes

• Expressed in classes, methods, and instances

• Based on purpose, not what it holds

What is problem decomposition?

Breaking a larger problem into smaller problems to produce a hierarchy chart.

Each smaller module should become a subroutine.

Advantages of problem decomposition/hierarchy charts:

• Understandable: clear purpose

• Reduces bugs and errors

• Maintainable: one change doesnt change all

• Collaboration

• Portabiltiy

• Reusability

Definition of OOP

An imperative programming paradigm that involves the capturing of information and code into objects.

They are responsible for their own data and the actions performed upon it.

Class versus object?

The class is the blueprint, which is adapted with specific attributes to become an object.

Example: Class = car, object = Mercedes

What is instantiation?

The process of creating an object from a class template.

What is inheritance?

When code is re-used from one class to another without affecting the original attributes.

Superclass vs subclass?

Superclass: The original attributes

Subclass: The extended attributes

What is encapsulation and why is it done?

The process of bundling data and methods in order to restrict access to it.

This is done to:

• provide privacy

• hide internal complexity

• restrict altering of the object from elsewhere

Static vs dynamic polymorphism?

Static: Allows methods in the same class to have the same name, as long as they have different parameters.

• Parameters can be different by amount, type, and colour

Dynamic: Allows methods in the same class to have the same name AND same parameters.

• Provides different functionality depending on whether they’re implemented by the superclass or subclass.

Two types of association and their symbols.

Aggregation (outlined diamond) and composition (solid diamond)

What is aggregation?

A weak type of association, where a class is a ‘container’ of other classes.

• Contained classes hold little dependency

• Still exist if the container is destroyed.

Example: Head teacher and teacher

What is composition?

A stronger type of association, where a class is a ‘container’ of other classes.

• There is high dependency on the container

• If it is destroyed, so are the contained classes.

Example: Building and a room

What are the three OOP design principles?

1. Favour composition over inheritance (flexibility)

2. Encapsulate what varies; methods should be subdivided as much as possible into potential subroutines.

3. Program to an interface not implementation. The programmer should focus on the code’s purpose, and not how it works.