Java null pointer exception after checking if null

Question

Can anybody explain how is it possible that I am getting null pointer exception thrown from this line of code:

if (data != null && data.isActive()) {

Body of method isActive() is just:

public Boolean isActive() 
{
  return active;
}

Thanks in advance.

is it possible that the `NPE` is thrown within or by `method()`? — Dragondraikk, May 05 '15 at 14:09
data may not be null, but `method()` might be throwing a NPE. post the method() code. — K139, May 05 '15 at 14:11
Are you sure that `NPE` is not thrown from within the `method() `? — PM 77-1, May 05 '15 at 14:11
It is possible that `data` is not null but `.method()` is failing. Your stack trace would prove this. Please supply more code or your full stacktrace. — Daniel Tung, May 05 '15 at 14:11
Does your `isActive` method returns `boolean` and `active` is `Boolean` (wrapper)? — mkrakhin, May 05 '15 at 14:13
The more information you supply the more likely we'll be able to help. Stacktrace please — Daniel Tung, May 05 '15 at 14:13
Your edit didnt help too much. Now we need all assignments to active variable — Ziker, May 05 '15 at 14:13
your `active` variable is null, and java gets NPE when tries to unbox null value — , May 05 '15 at 14:15
please post a SCCE (self contained, compilable example). that will help. — Jill, May 05 '15 at 14:16

score 13 · Accepted Answer · answered May 05 '15 at 14:19

In java, there's a thing called autoboxing, when primitive values are wrapped by object types and vice versa.

So, in your code there is a method:

public Boolean isActive() 
{
  return active;
}

note, that you are returning Boolean (object type), not boolean (primitive type).

and return value is going to be used in your if statement.

if (data != null && data.isActive()) {

when java meets data.isActive() in your if statement, it tries to convert Boolean value to primitive boolean value, to apply it for your logical operation.

But your active variable inside of your isActive() method is null, so java is unable to unbox this variable to boolean primitive value, and you get Null pointer exception.

whoever downvote my answer, please leave a comment, to let me know, what is wrong with my assumptions. Thank you. — , May 05 '15 at 14:22

Java null pointer exception after checking if null

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