Object-oriented and additional programming (A Level) flashcards

Topic 9: Object-oriented and additional programming

Class vs object

A class defines the attributes and methods common to a type of object; it is written once. An object is one instance of a class, with its own attribute values.

What are instantiation and a constructor?

Instantiation is creating an object from a class. The constructor is called on instantiation and initialises the object to a given state.

What is encapsulation?

Hiding how a class works and how it represents data from other classes, usually by making attributes private and accessing them through methods.

What are inheritance and overriding?

Inheritance: one class is a more specialised version of an existing class. Overriding: a base-class method is redefined in a subclass so subclass objects behave differently.

Inheritance vs association

"Is a more specialised kind of" means inheritance. "Uses" or "has a link to" means association, which is much weaker. A Ward is associated with its Patients; it is not a kind of Patient.

Public, private and protected access modifiers

Public (+): accessible from anywhere. Private (−): the class only. Protected (#): the class and its subclasses.

How are private and protected members written in Python?

Private: a double underscore prefix, which triggers name mangling. Protected: a single underscore prefix, which is a convention only.

Why use the object-oriented paradigm?

It models problems as interacting objects, protects data behind methods, lets subclasses reuse tested code, and lets each class be built and tested separately.