C# Fundation, Part 2

In this blog, following topics will be covered:

1. Classes & Objects

2. Constructors

3. Inheritance

4. Access Modifiers

5. Abstract

6. Virtual

7. Static

8. Sealed

9. Partial

 

1. Classes & Objects

 

2. Constructors

1. No void

2. Method name are the same with class name

ctor + Tab to bring code snip of constructor

 

Reference Types

 

OO: Object Oriented Programming

 

3. Inheritance

Classes inherit from System.Object by default, for example, class Employee : Object by default

 

4. Access Modifiers

 

5. Abstract

1. Can’t use new() keywork to create an instance

2. If member is abstract, MUST implement it by override it

 

6. Virtual

1. The way to support Polymorphism

2. base.Method(), can be used to execute the virtual Method() in parent’s class

Shape, Draw()	Circle, Draw()	Color
No Virtual	No Override	1 Red, 100 Green
Virtual	No Override	1 Red, 100 Green
Virtual	Override	101 Red

 

7. Static

1. Static member can only access by className.property => Calc._rand is allow

2. Static member can’t invoke the member through an object instance => a1._rand is not allow

3. Static member only has one copy of data, but instance field may has many (depends on how many instances has been created)

class Calc
{
  public Calc(int rate)
  {
    _rate = rate;
  }

  public decimal GetResult()
  {
    return(_rate * _rand.NextDouble());
  }

  private int _rate;
  static Random _rand = new Random();
}


Calc a1 = new Calc(5);

decimal result;
result = a1.GetResult();

 

8. Sealed

1. No one can inherit from a Sealed class

2. A lot of classes in .NET framework are Sealed class, System.String, for example

 

9. Partial

1. Span definitions in multiple files, and C# complier will merge them into one single class

2. LINQ to SQL & Entity Framework use a lot of partial methods