Packt

Question 1

What is an object ?

OOP concepts

Answer 1

• A core concept of OOP
• An instantiation of a CLASS
• Representation of a Real-World Object
• Properties - Identity, State, Behaviour
• Occupies space in memory
• Has a lifecyle
• Can communicate with other objects

Question 2

What is a Class ?

OOP concepts

Answer 2

• A core concept of OOP
• A blueprint for an Object - which can usually be instantiated multiple times
• Does not occupy space in memory
• Defines member fields and methods
• Can be of type Inner, Anonymous, Parent, Sub
• Should follow Single Responsibility principle

Question 3

What is an abstraction ?

OOP concepts

Answer 3

• Abstraction is a key OOP concept
• Abstraction is representation of the key features of something without details of underlying concrete implementation
• Abstraction is achieved through Interfaces and Abstract Classes

Question 4

What is encapsulation ?

OOP concepts

Answer 4

• Encapsulation is a key OOP concept
• It refers to restricting access to an object’s internal workings and state
• limiting to public exposure points
• Implemented by getters/setters and access modifiers
• Advantages - loosely coupled code, easier to test, secure

Question 5

What is Inheritance ?

OOP concepts

Answer 5

• Inheritance is a core concept of OOP
• Classes can be related
• It is possible to Inherit the fields of a parent class by using the keword extend
• Can only inherit from a single parent
• It is advantageous because it allows for code resuse

Question 6

What is Polymorphism ?

OOP concepts

Answer 6

• Polymorphism is a core concept of OOP
• Polymorphism means many forms
• There a two types of Polymorphism - runtime & compile time
• Runtime Polymorphism is implementing method overriding in a sub-class
• Compile Polymorphism is implementing method overloading

Question 7

What is association ?

OOP concepts

Answer 7

• Association is a core OOP concept
• Association refers to the relationship between two classes that are independent of each other e.g. Person & Address
• can be uni/bi directional, one-one, one-many, many-many

Question 8

What is aggregation ?

OOP concepts

Answer 8

• Aggregation is a key OOP concept
• It is a uni-directional relationship
• it is a “has-a” relationship as in Tennis Player “has-a” Raquet (but not the other way around

Question 9

What is composition ?

OOP concepts

Answer 9

• Composition is a core OOP concept
• It is a more restrictive form of aggregation
• It is a “has-a” relationship as in Car “has-a” Engine
• more restrictive because If Car is destoyed the Engine is destroyed also

Question 10

What is S in SOLID ?

OOP concepts

Answer 10

• S - Single Responsibility
• A CLASS should have only one responsibility

Question 11

What is O in SOLID ?

OOP concepts

Answer 11

• O - Stands for Open for Extension, Closed for modification

Question 12

What is L in SOLID ?

OOP concepts

Answer 12

• L - Stands for Liskov principle
• Derived types must be completely substitutable for base types

Question 13

What is the I in SOLID ?

OOP concepts

Answer 13

• Interface Segregation principle
• Clients should not be forced to implement unnecessary methods
• If necessary an Interface should be split into smaller Interfaces