Whether I should use Constant or ReadOnly or Static Variable, how to decide it, what are the reasons to choose Constant, ReadOnly or Static. It depends on the situation, usability and location to access. We are going to discuss each of these one by one and compare and check why we can use Constant and not the ReadOnly or Static variable. Why to use ReadOnly and not the Constant or Static variable or why we need to use the Static variable and not the Constant or ReadOnly.
If we want to declare a variable with fixed value at the time of declaration then we can use constant. Say we want to use state "NY" in our entire class then we can declare a variable and immediately assign the value to it with "NY".
Why cannot we use ReadOnly or Static in this situation?
Some valid declaration
const string STATE = "NY";
public const Single PI = 3.14159;
public const Single PI = 22/7;
public const double GRAVITATION = 6.673e-11;
//declare multiple constants
public const int CENTURY = 100, HATRIC = 3, OVER = 6;
Valid declaration of constants with constants
public const int c1 = 5;
public const int c2 = c1 + 100;
public const int c3 = c1 + c2;
public const int c4 = c1 + c2 + c3;
Some in-valid declaration
public const int PI = x;
public const int PI = x/y;
public const double DISCOUNT = (price /100 ) * 3;
const string city = GetFromDB();
Some real life examples where we cannot use constant:
A ReadOnly variable is similar to constant but we can assign the value either at the time of declaration or in the constructor. Suppose you don't know the value at the time of declaration but you will know it at the time of initializing the object then we can use ReadOnly.
Some valid declaration
public readonly int age = 27;
public readonly single pi = 22 / 7;
public class Person
{
readonly int _age;
public Person()
{
_age = GetAverageUserAge(); // from database
}
public Person(int age)
{
_age = age;
}
}
Invalid: try to change the readonly value in a method,
public class Age
{
readonly int _year;
Age(int year)
{
_year = year;
}
void ChangeYear()
{
_year = 1967; // Compile error.
}
}
Static fields and instance fields are two of the several kinds of variables supported by C#, and at times they are referred to as static variables and instance variables, respectively. A static field is not the part of any instance of the class, no matter how many instances of a class is created, there is only one copy of the static field, let's try to understand it with an example
public class Variable
{
public int x = 5;
public void test()
{
x = x + 5;
Console.WriteLine(x);
}
}
public class Exercise
{
static void Main()
{
var var = new Variable();
var.test();
var var1 = new Variable();
var1.test();
Console.ReadKey();
}
}
In this example I used x as a normal variable without static keyword, it will give the result 10 and 10
public class Variable
{
public static int x = 5;
public void test()
{
x = x + 5;
Console.WriteLine(x);
}
}
public class Exercise
{
static void Main()
{
var var = new Variable();
var.test();
var var1 = new Variable();
var1.test();
Console.ReadKey();
}
}
Now we used static keyword to declare the x variable, run the application and we will get 10 and 15 as a result.
It shows the static variable value shared among all the instances of the class.
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Having 13+ years of experience in Microsoft Technologies (C#, ASP.Net, MVC and SQL Server). Worked with Metaoption LLC, for more than 9 years and still with the same company. Always ready to learn new technologies and tricks.
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| By Ali Adravi On 03 Apr, 15 Viewed: 7,586 |
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