What will be the output of the following Java code?

public class Boxer1 
{
    Integer i;
    int x;
   public Boxer1(int y) 
   {
        x = i+y;
        System.out.println(x);
   }
   public static void main(String[] args) 
   {
       new Boxer1 (new Integer(4));
   }
}

A. The value "4" is printed at the command line

B. Compilation fails because of an error in line

C. A NullPointerException occurs at runtime

D. An IllegalStateException occurs at runtime

Answer: Option D