Object-Oriented Programming

Question 1

What is object-oriented programming?

Answer 1

An entirely modular to programming where everything in the program is implemented as an object which has attributes and properties (data) and methods (subroutines)

Question 2

What is encapsulation?

Answer 2

Data and subroutines for a single object are kept together and the data is controlled via methods that comprise the object’s interface

Question 3

What is a class?

Answer 3

The definition that continues what attributes and methods an object will have

Question 4

What is an object?

Answer 4

A specific instance of a class

Question 5

What is encapsulation in terms of object-oriented programming?

Answer 5

Combining a record with the procedures and functions that manipulate it to form a new data type (class)

Question 6

What is the constructor of a class?

Answer 6

The method called to instantiate an object of that class. There is an object that is returned from this and it can be stored in a variable

Question 7

What is information hiding?

Answer 7

Protecting an object’s internal state from being accessed by other parts of the program

Question 8

What are the access modifiers and how can they be represented in UML diagrams?

Answer 8

Public: +
Private: -
Protected: #

Question 9

What does the public access modifier mean?

Answer 9

Attribute or method can be accessed by objects of any other class within the program

Question 10

What does the private modifier mean?

Answer 10

Attribute or method can only be accessed by objects of the same class

Question 11

What does the protected modifier mean?

Answer 11

Attribute or method can be accessed by objects of the same class or other classes that inherit from it

Question 12

What is the format of a formal class definition?

Answer 12

ClassIdentifier = Class
Public
public attributes : types
public methods and procedures
Protected
protected attributes : types
protected methods
Private
private attributes : types
private methods
End

Question 13

What is the default for attributes and methods?

Answer 13

Private attributes and public getter methods

Question 14

What is inheritance in object-oriented programming?

Answer 14

A relationship between classes where a derived class gains the attributes and methods of the base class that it inherits from

Question 15

How to represent inheritance in a UML diagram?

Answer 15

Arrow pointing from derived to base class

Question 16

How to represent inheritance in a formal class definition?

Answer 16

DerivedClassIdentifier = Class (BaseClassIdentifier)

• only give additional methods in the definition or overriden methods

Question 17

What is polymorphism in OOP?

Answer 17

Polymorphism occurs when an inherited method (in a subclass) is redefined or overriden so that its implementation is different from its parent

Question 18

What is polymorphism (AQA definition)?

Answer 18

Polymorphism occurs when objects of different classes respond differently to the use of a common interface

Question 19

What are virtual methods?

Answer 19

Methods that can be overriden in inheritance

Question 20

What is method overriding?

Answer 20

Derived class inherits a method from the base class but implements it in a different way

Question 21

What are the key differences between virtual and abstract methods?

Answer 21

Virtual methods:
- Can be overridden by a child class
- Are implemented
- Can be declared in any class

Abstract methods:
- Must be overridden by a child class
- Have no implementation in the parent class
- Can only be declared in abstract classes

Question 22

How to declare an abstract class in C# and abstract method?

Answer 22

Abstract keyword

Question 23

What are the two types of association?

Answer 23

1) Aggregation - “weak”
2) Composition - “strong”

Question 24

What is composition?

Answer 24

Composition is a restricted form of association, where one object contains another. If the container object is deleted, the contained objects are also deleted.

Question 25

How is composition represented in a UML diagram?

Answer 25

A line between the two classes with a **black filled diamond** at the class which is the container (e.g. car to a wheel)

Question 26

What is aggregation?

Answer 26

Aggregation is a type of class where one class contains another. However, the **aggregated** objects exist **independently** of the aggregating object and will **not be deleted** from the program if the **aggregating object is deleted**.

Question 27

How is aggregation represented in a UML diagram?

Answer 27

A line between the two classes and a **white unfilled diamond** at the aggregating object (e.g. car for a driver).

Question 28

What are the key design principles in object-oriented programming?

Answer 28

1) Encapsulate things that frequently change 2) Favour composition over inheritance 3) Program to interfaces, not implementations

Question 29

What are static methods?

Answer 29

Class methods that can be called without the need to **instantiate an object** of that class // A method that doesn't rely on the **internal state** of a specific **object** of the class.

Question 30

What are the uses of static variables?

Answer 30

- Only stored once per class so less memory used - Autoincrementing between objects (e.g. for an ID)