Classes and members (C#)

Question 1

What does object orientated programming (OOP) mean?

Answer 1

It is when a programming language organizes code into objects, which are instances of classes.

It focuses on representing real-world entities as objects and their interactions through methods, properties, and events.

Question 2

Which concepts does OOP emphasize?

Answer 2

1. Encapsulation.
2. Inheritance.
3. Polymorphism.
4. Abstraction

Question 3

What is the difference between an object-oriented language and a non-object-oriented language?

Answer 3

An object-oriented language is designed to support object-oriented programming principles and features. It provides built-in constructs like classes, objects, inheritance, and polymorphism.

Non-object-oriented languages do not have these built-in constructs and instead rely on other programming paradigms like procedural or functional programming.

Question 4

Why is C# object-oriented?

Answer 4

It supports the fundamental principles of OOP.

It provides features like classes, objects, inheritance, polymorphism, encapsulation, and abstraction.

Question 5

What are classes in C#?

Answer 5

A class is a blueprint or template that defines the characteristics (data members) and behaviors (methods, properties, events) of objects.

It serves as a blueprint for creating instances of objects.

Question 6

What are structs in C#?

Answer 6

They are user-defined types in C#. However, they are value types rather than reference types like classes.

Structs are typically used for lightweight objects that don’t require inheritance or complex behavior.

Question 7

What are records in C#?

Answer 7

They are a brief way of defining immutable data types.

They automatically generate useful methods such as equality comparison, hashing, and string representation based on their properties.

Question 8

How do we use records in C#?

Answer 8

public record Person(string Name, int Age);

// Create a new instance of the record
var person = new Person(“John”, 30);

// Access properties
Console.WriteLine(person.Name); // Output: John
Console.WriteLine(person.Age); // Output: 30

Question 9

What are abstract classes in C#?

Answer 9

It is a class that cannot be instantiated directly.

It serves as a base class for other classes and provides a common interface or set of behaviors that derived classes must implement.

Abstract classes can contain both regular and abstract members.

Question 10

What are abstract members C#?

Answer 10

They are declared within an abstract class but do not provide an implementation.

Derived classes must override these members to provide their own implementation.

Example of abstract members:
Abstract methods or properties.

Question 11

What does the keyword “static” mean/do?

Answer 11

It is a keyword used to declare members (fields, methods, properties) that belong to the class itself rather than instances of the class.

Static members are shared among all instances of the class and can be accessed without creating an object of the class.

Question 12

What is evolving classes in C#?

Answer 12

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Question 13

What are partial classes in C# and why do we use them?

Answer 13

1. It is a class that can be split into multiple source code files. The partial keyword allows a class’s definition to be spread across multiple files, making it easier to organize and maintain large classes.
2. Partial classes are often used in code generation scenarios or when multiple developers need to work on different parts of a class simultaneously.

Question 14

What does the keyword “partial” mean/do?

Answer 14

It allows a class, struct, or interface to be defined in multiple files.

It allows the definition of a type to be split across multiple source code files, making it easier to organize and maintain large classes.

Question 15

What are the 4 object-oriented features?

Answer 15

1. Encapsulation.
2. Abstraction.
3. Inheritance.
4. Polymorphism.

Question 16

What is encapsulation and why use it?

Answer 16

It is the practice of bundling data and methods within a class and controlling access to them.

We use it, because it helps to protect data, organize code, and make it easier to maintain.

Question 17

What is abstraction and why use it?

Answer 17

It simplifies complex entities by focusing on essential aspects and hiding unnecessary details.

We use it because it helps to manage complexity, promote modularity, and create reusable code.

Question 18

What is inheritance and why use it?

Answer 18

It is a feature in object-oriented programming where a class can inherit properties and behaviors from another class.

We use it because it promotes code reuse, reduces duplication, and enables hierarchical organization and specialization of objects.

Question 19

What does specialization and generalization mean in relation to inheritance?

Answer 19

Specialization: This means creating specific classes from a general base class, inheriting and extending its properties and behaviors to meet specific needs.

Generalization: This means creating a more general base class by extracting common properties and behaviors from multiple specialized classes.

Question 20

What does it mean that inheritance is transitive?

Answer 20

It means that if class B inherits from class A, and class C inherits from class B, then class C also indirectly inherits all the members of class A.

Question 21

How does constructors work in inheritance?

Answer 21

Constructors are not inherited from the base class to the derived class.

However, when a derived class is instantiated, the constructor of the base class is called first to initialize the inherited members, and then the derived class’s constructor is executed to initialize its specific members.

Question 22

What is “preventing” inheritance and what does the keyword “sealed” mean/do?

Answer 22

The keyword “sealed” can be used to prevent a class from being inherited. When a class is marked as “sealed,” it cannot be used as a base class for other classes.

Question 23

What is polymorphism and why use it?

Answer 23

It allows objects of different types to be treated as if they were of the same type.

We use it because it provides code flexibility and enables generic programming.

Question 24

What is member hiding in polymorphism?

Answer 24

It is the act of declaring a member with the same name in a derived class to hide the base class member.

Question 25

What does the keyword “new” mean/do in relation to member hiding?

Answer 25

It is used to explicitly indicate the intention of hiding the base class member.

Question 26

What are the 5 SOLID principles?

Answer 26

1. Single responsibility principle
2. Open/closed principle.
3. Liskov Substitution Principle.
4. Interface Segregation Principle.
5. Dependency Inversion Principle.

Question 27

Explain the 5 SOLID principles.

Answer 27

Single responsibility principle: A class should have only one reason to change, meaning it should have a single responsibility or purpose.

Open/closed principle: Software entities (classes, modules, etc.) should be open for extension but closed for modification. This means that you should be able to add new functionality without modifying existing code.

Liskov Substitution Principle:
Derived classes should be able to replace their base classes without altering the correctness of the program.

Interface Segregation Principle:
Clients should not be forced to depend on interfaces they don’t use.

Dependency Inversion Principle:
High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details; details should depend on abstractions.

Question 28

What is visibility and why do we use it?

Answer 28

1. Visibility refers to how accessible members (such as fields, methods, and properties) in a class are. It determines who can access them and from where.
2. We use it, because it helps control access to sensitive information and keeps implementation details hidden.

Question 29

What is an access modifier?

Answer 29

It specifies the accessibility level of a member.

Question 30

Name and explain alle the access modifiers in C#.

Answer 30

public: The member is accessible from any other code.

private: The member is accessible only from within the same class.

protected: The member is accessible within the same class and its derived classes.

internal: The member is accessible within the same assembly (project).

protected internal: The member is accessible within the same assembly and its derived classes, both within and outside the assembly.

Question 31

Can you name some members in a class?

Answer 31

1. Fields.
2. Methods.
3. Properties.
4. Events.
5. Nested types (nested classes, structs, etc.).

Question 32

What are fields?

Answer 32

They are variables that hold data within a class.

They store the state of an object and provide the class with its attributes and data values.

Question 33

What does it mean when a field is marked as “read-only”?

Answer 33

It means that its value can only be assigned during object initialization or within the constructor.
Once assigned, it cannot be modified.

Question 34

How does fields grow into properties?

Answer 34

They can be encapsulated and exposed through properties. Properties provide a level of abstraction and allow controlled access to the underlying fields.

Question 35

What are constants?

Answer 35

They are fixed values that do not change during program execution.

Question 36

What is the subtle difference between const and read-only fields?

Answer 36

“Const” fields are evaluated and assigned at compile-time, while “read-only” fields can have their values assigned at runtime, typically within the constructor or object initialization.

Question 37

What are properties?

Answer 37

They are like special fields that have getter and setter methods.

With properties, you can get and set values as if you were directly accessing fields, but you can also add custom logic and validation.

Question 38

How do we use properties?

Answer 38

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Question 39

What are getters and setters?

Answer 39

Getters retrieve the value of a property.

Setters modify the value of a property.

Question 40

What does it mean when an object is initialized with “init”?

Answer 40

It means that the object can only be modified during object initialization but not afterward.

It provides a way to create immutable objects where the initial state is set during construction and remains unchanged.

Question 41

What are some auto-implemented properties?

Answer 41

They provide a shorter way to define properties without writing extra code for the backing fields.

Example:
public string Name { get; set; }

Question 42

What are constructers?

Answer 42

1. They initialize objects of a class.
2. They are called automatically when an object is created and typically allow you to set initial values for the object’s properties.
3. They have the same name as the class and may have parameters.

Question 43

What does the keyword “this” mean/do?

Answer 43

It refers to the current instance of the class being constructed.

It helps differentiate between instance variables and parameters with the same names.

Question 44

What are de-constructers?

Answer 44

1. They are also know as finalizers.
2. They clean up resources when objects are destroyed.

Question 45

What are finalizers?

Answer 45

They are special methods called when an object is being destroyed to release resources or perform cleanup tasks.

Question 46

What are methods?

Answer 46

They are functions in a class that perform specific tasks.

Question 47

What does the keyword “override” mean/do?

Answer 47

It indicates that a method in a derived class replaces the implementation of the same method in the base class.

Question 48

What is method hiding?

Answer 48

It happens when a method in a derived class has the same name as a method in the base class but provides a new implementation.

Question 49

What is static method dispatch and how do we use it?

Answer 49

It happens when a method in a derived class has the same name as a method in the base class but provides a new implementation.

Example:
public class BaseClass
{
public virtual void SomeMethod()
{
Console.WriteLine(“BaseClass SomeMethod”);
}
}

public class DerivedClass : BaseClass
{
public new void SomeMethod()
{
Console.WriteLine(“DerivedClass SomeMethod”);
}
}

class Program
{
static void Main(string[] args)
{
BaseClass derivedObjAsBase = new DerivedClass();
derivedObjAsBase.SomeMethod(); // Output: “BaseClass SomeMethod”
}
}

Question 50

What is virtual methods and explain the keyword virtual?

Answer 50

Virtual methods can be overridden by derived classes, and the “virtual” keyword allows this behavior.

Question 51

What are indexers?

Answer 51

They allow accessing elements or values in an object using index notation, like arrays.

Question 52

What are operators (overload)?

Answer 52

It lets you redefine the behavior of operators (+, -, *, /, etc.) for custom types.

Question 53

What are events?

Answer 53

They enable objects to notify other objects when specific actions or conditions occur.

Question 54

What are types?

Answer 54

They classify values or entities based on their characteristics or properties.

Question 55

What are anonymous types?

Answer 55

They allow creating objects without explicitly defining a named class.

Question 56

What are objects and how do we use them?

Answer 56

1. Objects are instances of classes and can be created with the “new” keyword.
2. They can be accessed, modified, and used to perform actions.

Question 57

What are object initializers?

Answer 57

They set initial property values of an object at creation using a concise syntax.

Question 58

What are collection initializers?

Answer 58

They initialize collections (lists, arrays, dictionaries) with values using a simplified syntax.