1. Introduction to .NET Florin Olariu
“Alexandru Ioan Cuza”, University of Iași
Department of Computer Science

2. Agenda OOP in .NET Core Arrays Generic list What’s Next
Demo
Generic list
What’s Next
Interview questions

3. OOP in .NET Core
Inheritance
Inheritance
Classes may derive from exiting classes.
Existing classes are called : parent class. => and it is a generalization of the exiting class.
Inheritance creates an “is –a ” relationship
Example: Employee<=Manager, Architect, Technical Lead, Developer

4. OOP in .NET Core – inheritance
Derived class indicates base class with colon.
Notes:
classes can contain properties and fields (built-in like int, string or custom like other classes or struct’s)
Fields are used to support private methods
Properties are used to expose functionality to other classes

5. OOP in .NET Core - inheritance
Identify : properties, methods/behavior

6. OOP in .NET Core - polymorphism
The possibility of taking many forms.
Method overriding -> modify a method in the derived class : C# in order to be able to use method overriding we need to know: virtual  override.
Virtual exists in base class, override in derived class.

7. OOP in .NET Core - polymorphism

8. OOP in .NET Core - polymorphism
Another important aspect for polymorphism is “method overloading”.
Means: we can have in the same class methods with the same name but different number of parameters.

9. OOP in .NET Core - encapsulation
Encapsulation : a class should have a single responsibility. => don’t forget here, there is another set of principles : SOLID.
Within the class we should have private functionality, that should not be exposed and only a : few well-defined methods that are public.
Question: Why the method should be public?

10. OOP in .NET Core Inheritance Polymorphism Encapsulation
There are 3 pillars in OOP. => Inheritance, polymorphism and encapsulation.

11. OOP in .NET Core
"In the one and only true way. The object-oriented version of 'Spaghetti code' is, of course, …."

12. OOP in .NET Core
"In the one and only true way. The object-oriented version of 'Spaghetti code' is, of course, 'Lasagna code'."
- Roberto Waltman.

13. Arrays

14. Arrays Definition Declaring and populating an array
Samples
Declaring and populating an array
Using collection initializers
Retrieving an element from an array
Iterating an array
Using array methods
Best practices
Demo

15. Arrays
Definition

16. Arrays
Definition
Is a fixed-size list of elements that can be accessed using a positional index number

17. Arrays Red “Salt” 2.21 White “Pepper” 3.43 Definition “Onion” 5.01
Is a fixed-size list of elements that can be accessed using a positional index number
Sample:
Red
White
Green
Blue
“Salt” 2.21
“Pepper” 3.43
“Onion” 5.01
“Garlic” 3.20
Notes:
1. In arrays index is “0-based”.
2. Arrays are fixed size.(we will define the size of an array when this is initialized – once is initialized the size cannot be adjusted)

18. Arrays Definition 1 2 3 Red White Green Blue 1 2 3 “Salt” 2.21
Is a fixed-size list of elements that can be accessed using a positional index number
Sample: 1 2 3
Red
White
Green
Blue 1 2 3
“Salt” 2.21
“Pepper” 3.43
“Onion” 5.01
“Garlic” 3.20
Notes:
In arrays index is “0-based”.

19. Arrays
Definition
Samples
Declaring and populating an array

20. Arrays Red White Definition Green Declaring and populating an array
Samples
Declaring and populating an array
Declaring an array:
string[] colors;
Red
White
Green
Blue

21. Arrays Red White Green Blue Definition
Samples
Declaring and populating an array
Declaring an array: Initializing an array:
string[] colors; string[] colors;
colors = new string[4];
string[] colors = new string[4];
var colors = new string[4];
Red
White
Green
Blue
An array is a reference type.
In this case we should use: “new” keyword for initialization.

22. Arrays Definition Declaring and populating an array Samples

23. Arrays Definition Declaring and populating an array Samples
var colors = new string[4];
colors[0] = “Red”;
colors[1] = “White”;
colors[2] = “Green”;
colors[3] = “Blue”;
An array is a reference type.
In this case we should use: “new” keyword for initialization.

24. Arrays Best practices Do Avoid
Use arrays when the size is known at the design time
Do not use arrays when the data comes from a database call
For an array name use ‘pluralization’ => Colors

25. Arrays
Demo

26. Generic List

27. Generic List Definition Arrays vs Generic List
Declaring and populating Generic Lists
Using initializers
Retrieving elements from Generic lists
Iterating through a Generic List
Demo

28. Generic List Definition
It is a strongly typed list of elements that is accessed using a positional index number.

29. Generic List
Arrays vs Generic List

30. Generic List
Arrays vs Generic List
Arrays
Generic List

31. Generic List
Arrays vs Generic List
Arrays
Generic List
Strongly typed

32. Generic List Arrays vs Generic List Arrays Generic List Strongly typed
Fixed length
Expandable

33. Generic List Arrays vs Generic List Arrays Generic List Strongly typed
Fixed length
Expandable
The is no ability to add/remove elements
Can add, insert or remove elements

34. Generic List Arrays vs Generic List Arrays Generic List Strongly typed
Fixed length
Expandable
The is no ability to add/remove elements
Can add, insert or remove elements
Multi-dimensional
One-dimensional

35. Generic List
Declaring and populating Generic Lists

36. Generic List
Declaring and populating Generic Lists

37. Generic List Declaring and populating Generic Lists
This is using Collection initializer.

38. Generic List Frequently asked questions
When is appropriate to use a generic list?

39. Generic List Frequently asked questions
When is appropriate to use a generic list?
Any time the application needs to manage a list of things
What are the key differences between an array and a generic list?

40. Generic List Frequently asked questions
When is appropriate to use a generic list?
Any time the application needs to manage a list of things
What are the key differences between an array and a generic list?
An array is fixed length and can have multiple dimensions
A generic list can have any length and provides methods to add, insert or remove elements
Execution time

41. Generic List Frequently asked questions
When is appropriate to use a generic list?
Any time the application needs to manage a list of things
What are the key difference between an array and a generic list?
An array is fixed length and can have multiple dimensions
A generic list can have any length and provides methods to add,insert or remove elements
Execution time
For this samples I used:
List<int> list = new List<int>( );
The second number is a checksum to verify they all did the same work.
static class Program {
static void Main()
Random rand = new Random(12345);
for (int i = 0; i < ; i++)
list.Add(rand.Next(5000)); }
int[] arr = list.ToArray();
int chk = 0;
Stopwatch watch = Stopwatch.StartNew();
for (int rpt = 0; rpt < 100; rpt++)
int len = list.Count;
for (int i = 0; i < len; i++)
chk += list[i];
watch.Stop();
Console.WriteLine("List/for: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
chk = 0;
watch = Stopwatch.StartNew();
for (int i = 0; i < arr.Length; i++)
chk += arr[i];
Console.WriteLine("Array/for: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
foreach (int i in list)
chk += i;
Console.WriteLine("List/foreach: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
foreach (int i in arr)
Console.WriteLine("Array/foreach: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
Console.ReadLine();
List/for: 1971ms ( ) Array/for: 1864ms ( ) List/foreach: 3054ms ( ) Array/foreach: 1860ms ( )

42. Generic List
Demo

43. What’s next …
Generic dictionaries
Generic collection interfaces
LINQ

44. Interview questions Abstract classes vs Interfaces Boxing/Unboxing
Immutable string

45. One more thing…
 "Walking on water and developing software from a specification are easy…"

46. One more thing…
  "Walking on water and developing software from a specification are easy if both are frozen."
- Edward V Berard

47. Questions
Do you have any other questions?

48. Thanks! See you next time! 