Section 12 - Object-Orientated Programming - USE NOTES

Question 1

What is a procedural language?

Answer 1

A program consisting of:
- Step-by-step instructions
- Function and procedure calls
- Local and global variables

Question 2

How does procedural programming work?

Answer 2

Code is broken down into a number of smaller modules, with the program consisting of a series of calls to procedures and functions, each of which may in turn call other procedures or functions

Question 3

How does object orientated programming work?

Answer 3

The world is viewed as a system of objects, each of which is responsible for its own data and the operations on that data. All processing carried out is done by the objects

Question 4

What are attributes?

Answer 4

Data that is associated with the class

Question 5

What features do objects have?

Answer 5

• Attributes
• State
• Behaviours

Question 6

What are states?

Answer 6

The value of an objects instance variables

Question 7

What are behaviours?

Answer 7

Actions that can be performed by an object

Question 8

What is a class?

Answer 8

A blueprint or template for an object that defines the attributes and behaviours of those objects

Question 9

What is a method?

Answer 9

Attributes and behaviours of an object, they are the functionality of a class

Question 10

What is a constructor?

Answer 10

Something used to create objects in a class

Question 11

What are setter methods?

Answer 11

Procedures

Question 12

What are getter methods?

Answer 12

Functions

Question 13

What is instantiation?

Answer 13

Where a new object (an instance of a class) is created

Question 14

Can multiple instances of the same class be created?

Answer 14

Yes, they will share identical methods and attributes, however the value of their attributes will be unique to each instance

Question 15

What is a reference type variable?

Answer 15

Variables that hold a pointer or reference to where the object itself is stored

Question 16

What is a variable reference diagram?

Answer 16

A graphical form showing how objects are referenced by reference variables

Question 17

What is an instance of a class?

Answer 17

Objects created from that class

Question 18

What is encapusaltion?

Answer 18

All the data and methods of an object are combined into a single entity so that the attributes or behaviours of one object cannot affect the way in which another object functions

Question 19

What is a subclass?

Answer 19

A “child” class in object-orientated programming

Question 19

Why do programmers use encapsulation?

Answer 19

• Different programmers can work on different classes and not have to worry about how other parts of the system may affect any code they write
• They can use methods from other classes without having to know how they work

Question 20

How can you determine whether to use inheritance?

Answer 20

Use the “is a” rule. Ask “is object A an object B?”, and if it is then object A should inherit the data and behaviours from object B

Question 21

What is a superclass?

Answer 21

A “parent” class in object-orientated programming

Question 21

What is an inheritance diagram?

Answer 21

A diagram showing the inheritance relationship between different classes

Question 21

What is inheritance?

Answer 21

Child classes inherit data and behaviours from their parent class

Question 22

What is association?

Answer 22

A “has a” relationship between classes, meaning there is no ownership between objects and they can be created and deleted independently

Question 23

What is aggregation?

Answer 23

A more specific interpretation where a class is a collection or container of other classes, however they do not have a lifecycle dependency

Question 24

What is composition?

Answer 24

A stronger form of association, where if the container object is destroyed then every instance of the contained class is also destroyed

Question 25

How is aggregation shown in class diagrams?

Answer 25

A hollow diamond shape next to the container object

Question 26

How is composition shown in class diagrams?

Answer 26

A filled in diamond shape next to the container object

Question 27

What is polymorphism?

Answer 27

A programming languages ability to process objects differently depending on their class.

Question 28

What is overriding?

Answer 28

Defining a method with the same name and formal argument types as a method inherited from a superclass

Question 29

Why is composition favoured over inheritence?

Answer 29

• It allows for greater flexibility as composition is a less rigid relationship between the 2 objects
• An object may be composed of several other objects but cannot be said in a real-world sense to “inherit” their characteristics

Question 30

What is information hiding?

Answer 30

Where the objects instance variables are hidden so other objects must use messages to interact with that object’s state

Question 31

What are the 3 access modifiers?

Answer 31

• Public
• Private
• Protected

Question 32

What can access a method/instance variable that has been declared public?

Answer 32

Code within any class

Question 33

What can access a method/instance variable that has been declared private?

Answer 33

Code within the class itself can access it

Question 34

What can access a method/instance variable that has been declared protected?

Answer 34

The definition varies between languages, however the most common definitions are only members of the same subclass, and only members in the same package/library of classes

Question 35

What is an interface?

Answer 35

A collection of abstract methods that a group of unrelated classes may implement

Question 36

What is the advantage of using an interface?

Answer 36

New classes can be added which use the interface without affecting existing classes

Question 37

What is the point of encapsulating what varies?

Answer 37

It reduces maintenance and testing effort

Question 38

What is encapsulating what varies?

Answer 38

When something changes in a program, if the concept in question is encapsulated in a single module then only that module needs to change

Question 39

What are the advantages of OOP?

Answer 39

• The object-orientated methodology forces programmers to go through extensive planning, making better designs with less weaknesses
• Encapsulation means that source code for an object can be written, tested and maintained independently of the code for other objects
• Once an object is created, knowledge of how its methods are implemented is no necessary for it to be used
• New objects with small differences to existing ones can be created easily
• Objects that are already defined, coded and tested can be reused in other programs
• An object-orientated program is much easier to maintain because of its modular structure