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.
|
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.
|
| By Ali Adravi On 03 Apr, 15 Viewed: 7,633 |
In C# there are different data type and they use some default value when we declare a variable. When we define a variable of type int or Int32 say int score; so what is the value of score, will it be null or zero, in the same way if we create a variable of type string/String what value it holds... By Ali Adravi On 27 Mar 2013 Viewed: 2,615
An enumeration type (also known an enumeration or an enum) provides an efficient way to define a set of named integral constants that may be assigned to a variable to make programming clear, understandable and manageable. There are ways of using, like how to use enum in switch and case statement,... By Hamden On 27 Mar 2013 Viewed: 4,571
When we have var which dynamically holds any type or value so why we need dynamic type, what are the differences and situations where we can use dynamic rather than var, there were some question in my mind so I explored more which I want to share here. There are two things, static type and... By Nathan Armour On 26 Mar 2013 Viewed: 3,219
An array can be initialized in several ways, it can store a single value or series of values, every element must be set of same type, C# supports single-dimensional arrays, multidimensional arrays (also call rectangular array) and array-of-arrays (referred jagged arrays), let’s discuss features of... By Ali Adravi On 24 Mar 2013 Viewed: 4,379
When there was XmlDocument why we need XDocument, is there any better feature available with XDocument, answer is yes, XDocument has a number of benefits, easy to create, easy to update, easy to search, ability to use LINQ to XML, cleaner object model etc. In this post we will see some examples... By Ali Adravi On 16 Mar 2013 Viewed: 3,523