Null pointer exception

Question

compiler giving NullPointerException error, dont know why. please help?

public List<DBObject> findByDateDescending(int limit) {

    List<DBObject> posts = null;
    // XXX HW 3.2,  Work Here
    // Return a list of DBObjects, each one a post from the posts collection
    DBCursor cur=postsCollection.find().sort(new BasicDBObject("date",-1)).limit(limit);
   while(cur.hasNext()){
/*==>> error */   posts.add(cur.next());
    }//end while 

    return posts;
}

You did assign only `null` to `posts`, and then you try to access it, of course you get NPE. — amit, Apr 05 '14 at 20:13
[What is a NullPointerException?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception). And the official docs: [NullPointerException](http://docs.oracle.com/javase/7/docs/api/java/lang/NullPointerException.html) — keyser, Apr 05 '14 at 20:14
Next time, look at your stack trace. Then read [`NullPointerException`](http://docs.oracle.com/javase/7/docs/api/java/lang/NullPointerException.html), then put 2 and 2 together and watch the magic happen. There's only two opportunities on that line for an NPE; either `posts` or `cur` is `null`. We can easily rule out `cur` since the line before it did not have an issue. So `posts` is `null`. Make it not be `null`. — Jason C, Apr 05 '14 at 20:15

score 3 · Answer 1 · answered Apr 05 '14 at 20:13

3

Change this:

List<DBObject> posts = null;

To this:

List<DBObject> posts = new ArrayList<DBObject>();

answered Apr 05 '14 at 20:13

barak manos

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hey man, thanks it worked!! what was the error? – exgenome Apr 05 '14 at 20:17
@exgenome: You're welcome. The error, as explained in the comments to your question, is that you are not initializing the `post` variable. To be more accurate, you are initializing it to `null`, hence the Null-Pointer exception that you get during runtime. I thought it was pretty obvious from the answer, so I didn't bother to explain it... Don't forget to click the V in order to accept the answer :) – barak manos Apr 05 '14 at 20:20

Null pointer exception

1 Answers1