Why is 1 the answer here?

Question

Could anyone explain why the output of this is 1?

public class A{
int i;
public A(){i++}
public void count(){
System.out.print(i);
}
}
public class Program{
public class void main(String[] args){
A obj1 = new A();
A obj2 = new A();
obj2.count();
}
}

I would expect an error, as i is declared but not initialised anywhere. So value of i would be undefined. Then in the constructor of A, when we try to do i++, that is i = i +1 = undefined + 1.
As far as I know doing arithmetic on undefined results in an error. Am I wrong here? And why?

Answer 1

Ok, the irony of finding the answer yourself straight away after you post the question is present here.

As it turns out, declared but not initialised variables will get a default value in java.
The default value for int is 0.

Then because i is an instance variable, separate for each objects:
initial value for i after creation of obj2 is 0 (similarly to obj1)
and only the instace variable of obj2 is increases by .count() method. so obj2.i is 1

http://www.c4learn.com/java/java-default-values/

Answer 2

C, C++ and Java (as far I know) don't have the integer value undefined. Undefined values are usually set to zero. That's all...