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NullPointerException

Sujatha Musunuri
Greenhorn

Joined: Oct 23, 2007
Posts: 16
1. public class Boxer1 {
2. Integer i;
3. int x;
4. public Boxer1(int y) {
5. x=i+y;
6. System.out.println(x);
7. }
8. public static void main(String[] args) {
9. new Boxer1(new Integer(4));
10. }
11. }

The Ans for this is 'NullPointerException' at runtime. Can some one let me know why is it giving that Exception?
Freddy Wong
Ranch Hand

Joined: Sep 11, 2006
Posts: 959

Since you didn't initialize the Integer i, by default i will be null. Hence, you get the NullPointerException when trying to perform the addition.


SCJP 5.0, SCWCD 1.4, SCBCD 1.3, SCDJWS 1.4
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Bert Bates
author
Sheriff

Joined: Oct 14, 2002
Posts: 8813
    
    5
Hi there Musu Musu,

Please help us out with two things:

1 - is that your real name? If not, please change your display name to be your first and last name. That's the policy at the ranch and it keeps things friendlier.

2 - it's great to post mock questions to discuss, but please indicate where you got the question when you post it - it's kind to the autor of the qeustion, and it can help us help you.

Thanks,

Bert


Spot false dilemmas now, ask me how!
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Kelvin Chenhao Lim
Ranch Hand

Joined: Oct 20, 2007
Posts: 513
Hi Musu,
Auto-unboxing a null reference will always cause a NullPointerException.


SCJP 5.0
 
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subject: NullPointerException