Why NullPointerException occur in short IF

Question

I written short Java code which cause NullPointerException. Does anybody have explanation for this? Code:

int val = 2;
Boolean result = (val == 0) ? false : ((val == 1) ? true : null);

Also following (simplified version) code will cause NullPointerException:

Object result = (false) ? false : (false ? true : null);

But this:

int val = 2;
Boolean result = (val == 0) ? Boolean.FALSE : ((val == 1) ? true : null);

and this:

Object result = (false) ? Boolean.FALSE : (false ? true : null);

or this:

Object result = (false) ? (Boolean)false : (false ? true: null);

doesn't?

`((val == 1) ? true : null)` here change `null` to `false`?? — noMAD, Jun 07 '13 at 17:08
Use `boolean` rather than `Boolean` to avoid many NullPointerExceptions — AllTooSir, Jun 07 '13 at 17:10
@TheNewIdiot I wanted have possibility to have three values in Boolean: true, false and null for error detection. — Jokii, Jun 07 '13 at 18:16

score 4 · Answer 1 · edited May 23 '17 at 12:06

4

I think what's happening is that ((val == 1) ? true : null) always returns null and it then tries to unbox that into a boolean. That causes a null pointer exception.

After I said this, @JonSkeet marked your question as a duplicate because of NullPointerException in ternary expression with null Long The answer there has a much more detailed explanation.

edited May 23 '17 at 12:06

Community

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answered Jun 07 '13 at 17:13

Daniel Kaplan

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So why changing `false` to `Boolean.FALSE` in example fix NPE? – Jokii Jun 07 '13 at 18:23

score 0 · Answer 2 · answered Jun 07 '13 at 17:16

0

int val = 2;

boolean result = (val==o)? false:true; // remove null from code and replace it with true.

answered Jun 07 '13 at 17:16

Nash

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score -1 · Answer 3 · answered Jun 07 '13 at 17:12

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In java, boolean allows only true and false but Boolean allows true false and NULL

answered Jun 07 '13 at 17:12

noMAD

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so, whats the reason for NPE? – sanbhat Jun 07 '13 at 17:14
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Oh snap, wanted this to be a comment and not an answer. @___@ – noMAD Jun 07 '13 at 17:17

Why NullPointerException occur in short IF

3 Answers3