Role of the constuctor

Hi, can somebody tell me why the following happens:

I have a class A

Code (csharp):

1. public class ClassA : MonoBehaviour {
2.     protected int i = 1;
3. }

and three classes B, C and D which derives from A.

Code (csharp):

1. public class ClassB : ClassA {
2.     public void Print(){
3.         Debug.Log("B: " + i);
4.     }
5.  
6.     public void Start(){
7.         Print();
8.     }
9. }

Code (csharp):

1. public class ClassC : ClassA {
2.     public ClassC(int j){
3.     }
4.    
5.     public void Print(){
6.         Debug.Log("C: " + i);
7.     }
8.    
9.     public void Start(){
10.         Print();
11.     }
12. }

Code (csharp):

1. public class ClassD : ClassA {
2.     public ClassD(){}
3.     public ClassD(int j){
4.     }
5.    
6.     public void Print(){
7.         Debug.Log("D: " + i);
8.     }
9.  
10.     public void Start(){
11.         Print();
12.     }
13. }

The output for running this (one game object with B and one with C) is:

C: 0
D: 1
B: 1

Why hasn't i been initialised in C?

 

Yes, I know that. My question is why?

 

Ahh, I think I understand now. The unity "side" of the object exists, and it can call Print(), but since I have declared a constructor I no longer get the default one and mono can't figure out how to create the object as there are no zero argument constructor, and hence the null value of i.