How can I avoid this NullPointerException?

Question

I have the following situation, where my program terminates with a NullPointerException during the function. What can I do to make this function work?

UPDATE

else if (str == null)
    emptyLinks.add(newPageLinks.get(i).getText() + "at link: " + str);

See this question: http://stackoverflow.com/questions/2601978/how-to-check-if-my-string-is-equal-to-null — MC10, Jul 27 '15 at 15:42
`str == null` should not give you a nullpointer exception for a null String — BoDidely, Jul 27 '15 at 15:42
if String is null, it points to no memory object. That is why you cannot call any method because there is no object. And thats why you are getting NPE — Vishwajit R. Shinde, Jul 27 '15 at 15:44
Shouldn't your code only execute if `str != null`? Why would you want to concatenate a null String? — BoDidely, Jul 27 '15 at 15:55
@SotiriosDelimanolis this is not a duplicate and those answers on the other page are not even close to a help. — Source Code, Jul 27 '15 at 18:48
You'd think so, but you'd be wrong. A `NullPointerException` occurs for one reason only, dereferencing a `null` value. You've posted some piece of code where 4 things could be `null`. We are not a debugging service. Read the duplicate, understand what a NPE is and use the details there to identify what is `null` in your code. — Sotirios Delimanolis, Jul 27 '15 at 18:51
The answers you've received below are essentially stating the same thing. — Sotirios Delimanolis, Jul 27 '15 at 18:52

brso05 · Accepted Answer · 2015-07-27T15:54:33.520

1

The problem is not in:

else if (str == null)

The actual problem is in:

do something

In your do something you are trying to access a property or method of a null object which isn't possible and will throw an NPE.

Normally if you want to access methods from an object that could be null you do a null check like so:

if (str != null)
do something

edited Jul 27 '15 at 15:54

answered Jul 27 '15 at 15:46

brso05

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I have added my do something function to my question, can you help me with this? – Source Code Jul 27 '15 at 15:54
@SourceCode the problem isn't `str` probably either `emptyLinks` is null or `newPageLinks` is null look at your stacktrace it should help you... – brso05 Jul 27 '15 at 15:56
emptyLinks is an empty queue.. how can I add this string to it? – Source Code Jul 27 '15 at 16:01
Why the downvote please specify why if you downvote someone. – brso05 Jul 27 '15 at 17:31

score 1 · Answer 2 · answered Jul 27 '15 at 15:47

If you use str == null the NullPointerException shouldn't be thrown. You can use:

 if (str == null || str.equals("null"))
    do something

If first condition is true then second conditions won't be evaluated and the exception won't be thrown.

Probably your problem is in do something when the str is null.

How can I avoid this NullPointerException?

2 Answers2