Uses of the Static Keyword in C#.NET (Static Constructors)

As you know, constructors are used to set the value of a type’s data at the time of construction. If you were to assign the value to a piece of static data within an instance-level constructor, you would be saddened to find that the value is reset each time you create a new object! For example, assume you have updated the SavingsAccount class as so:

class SavingsAccount
{
 public double currBalance;
 public static double interestRate;
 public SavingsAccount(double balance)
 {
     currBalance = balance;
     interestRate = 0.04;
 }
 //...
}

If you execute the previous Main() method, you will see a very different output. Specifically notice how the currInterestRate variable is reset each time you create a new SavingsAccount object.

While you are always free to establish the initial value of static data using the member initialization syntax, what if the value for your static data needed to be obtained from a database or external file? To perform such tasks requires a method scope to author the code statements. For this very reason, C# allows you to define a static constructor:

class SavingsAccount
{
   //...  
   // Static constructor.  
   static SavingsAccount()
   {
       Console.WriteLine("In static ctor!");
       currInterestRate = 0.04;
   }
}

Few points of interest regarding static constructors are:

• A given class (or structure) may define only one single static constructor.
• A static constructor is executed exactly one time, no matter of how many objects of the type are created.
• A static constructor does not take an access modifier and cannot take any parameters.
• The runtime invokes the static constructor when it creates an instance of the class or before accessing the first static member invoked by the caller.
• The static constructor executes before any instance-level constructors.

Given this modification, when you create new SavingsAccount objects, the value of the static data is preserved, and the output is identical to the output of the Static data program output.