Question on Integer type

[Sneha Kapoor]

Hi All,

  
 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));
 }
 }

Options are 

A. The value "4" is printed at the command line.
B. Compilation fails because of an error in line 5.
C. Compilation fails because of an error in line 9.
D. A NullPointerException occurs at runtime.
E. A NumberFormatException occurs at runtime.
F. An IllegalStateException occurs at runtime.

 

I thought answer would be 4 but answer is D

Can anyone please explain

Source : Whizlabs simulator

Thanks

[Sagar Rohankar]

Rule : Instance class variables, if not initializes, assign null object and instance primitive variable, if not initialize, get assigned default (0) value.

[Vijitha Kumara]

Integer i;    

What this i refers to at runtime? That would give you the answer.

[Sneha Kapoor]

Thanks got it

I was null hence got null pointer

[ram prabu]

hi

The primitive instance variable default value is 0 (if not explicitly declared).
int i;
now i value is 0

Wrapper instance variable default value is null. Because the wrapper is object

Integer i;

now i value is null

Now the answer is null pointer exception because you are adding (null+value). No way to add by this way.

Thanks
Ram

[Till Stoschus]

Hi "ram prabu"

but the exception is thrown because the implicit Method call i.intValue() in "x = i+y;" refers on a null-value, right?

Till

[ram prabu]

hi
yes till
we got null pointer exception when we are adding null with value.

Thanks
Ram