Static class and static class member (c #, summarized from MSDN)

1. Static class

1.1 Introduction

• Static classes and class members are used to create data and functions that can be accessed without the need to create class instances.
• Static class members can be used to separate data and behavior independent of any object identifier: No matter what changes occur to the object, the data and functions will not change.
• When the class does not depend on the data or behavior of object identifiers, you can use static classes.

Features 1.2

• They only contain static members.
• They cannot be instantiated.
• They are sealed.
• They cannot contain instance Constructors (C # programming guide ).

1.3 others

• Static classes are sealed and therefore cannot be inherited.
• A static class cannot contain constructor, but can still declare a static constructor to assign an initial value or set a static state.

1.4 instance

 static class CompanyInfo
{
public static string GetCompanyName() { return "CompanyName"; }
public static string GetCompanyAddress() { return "CompanyAddress"; }
//...
}

 

 

2. Static class members

2.1 Introduction

• Use the static keyword to declare a static class member before the return type of the member.
• You can call static methods, fields, attributes, or events in the class even if no instance of the class is created.

 Features 2.2

• If any instance of this class is created, the instance cannot be used to access static members.
• Only one copy of static fields and events exists. Static methods and attributes can only access static fields and static events.
• Static members are usually used to represent data or calculations that do not change with the object state. For example, a mathematical library may contain static methods used to calculate the sine and cosine.
• Static members are initialized before they are accessed for the first time and before any static Constructor (for example, called.
• To access a static class member, use the class name instead of the variable name to specify the position of the Member.

2.3 instance

Code: static class member Definition

 public class Automobile
{
public static int NumberOfWheels = 4;
public static int SizeOfGasTank
    {
get
        {
return 15;
        }
    }
public static void Drive() { }
public static event EventType RunOutOfGas;

//other non-static fields and properties...
}

 

Usage:

  Automobile.Drive();
int i = Automobile.NumberOfWheels;
3. An instance that uses static and static class members
The following is an example of a static class, which contains two methods to perform back-and-forth conversion between the Celsius and Fahrenheit temperatures:
Code
   public static class TemperatureConverter
{
public static double CelsiusToFahrenheit(string temperatureCelsius)
    {
// Convert argument to double for calculations.
        double celsius = System.Double.Parse(temperatureCelsius);

// Convert Celsius to Fahrenheit.
        double fahrenheit = (celsius * 9 / 5) + 32;

return fahrenheit;
    }

public static double FahrenheitToCelsius(string temperatureFahrenheit)
    {
// Convert argument to double for calculations.
        double fahrenheit = System.Double.Parse(temperatureFahrenheit);

// Convert Fahrenheit to Celsius.
        double celsius = (fahrenheit - 32) * 5 / 9;

return celsius;
    }
}

class TestTemperatureConverter
{
static void Main()
    {
        System.Console.WriteLine("Please select the convertor direction");
        System.Console.WriteLine("1. From Celsius to Fahrenheit.");
        System.Console.WriteLine("2. From Fahrenheit to Celsius.");
        System.Console.Write(":");

string selection = System.Console.ReadLine();
double F, C = 0;

switch (selection)
        {
case "1":
                System.Console.Write("Please enter the Celsius temperature: ");
                F = TemperatureConverter.CelsiusToFahrenheit(System.Console.ReadLine());
                System.Console.WriteLine("Temperature in Fahrenheit: {0:F2}", F);
break;

case "2":
                System.Console.Write("Please enter the Fahrenheit temperature: ");
                C = TemperatureConverter.FahrenheitToCelsius(System.Console.ReadLine());
                System.Console.WriteLine("Temperature in Celsius: {0:F2}", C);
break;

default:
                System.Console.WriteLine("Please select a convertor.");
break;
        }
    }
}
 
Input
2
98.6
Output:
Please select the convertor1. From Celsius to Fahrenheit.2. From Fahrenheit to Celsius.: 2
Please enter the Fahrenheit temperature: 98.6
Temperature in Celsius: 37.00