why am i getting Null Pointer Exception?

Question

I am fetching data from a database using this code :

Cursor cursor = db.query(News_Table, null, null, null, null, null, null);

if (cursor != null) 
{
    cursor.moveToFirst();
}
allNews = new News[cursor.getCount()];
int i = 0;

while (!(cursor.isLast())) 
{
    allNews[i] = new News(cursor.getInt(0), cursor.getString(2),
            cursor.getString(1));
    cursor.moveToNext();
    i++;
}

This is how my table looks : enter image description here

But everytime my last row is not being fetched and i get a null pointer exception. Here is the log cat screen : enter image description here

Why is my code running only for n-1 rows correctly and giving a problem on the (n)th row, where n is the total number of rows in my news table.

You check cursor != null and then three lines later use it as if it couldn't be null with cursor.getCount() either the null check isn't required, or your code cannot handle null values. — Peter Lawrey
– Peter Lawrey, Commented Jan 16, 2013 at 21:36

superfell · Accepted Answer · 2013-01-16 20:56:26Z

4

cursor.isLast() will return true when the cursor is on the last row, and so your while loop will stop at that point having not read & processed the last row. typically the pattern for iterating a cursor would be (note this doesn't call moveToFirst() either)

Cursor cursor = getACursor();
int i = 0;
while (cursor.moveToNext()) {
   /// do something with this row
   allNews[i] = new News(cursor.getInt(0), cursor.getString(2),cursor.getString(1));
   i++;
}

answered Jan 16, 2013 at 20:56

superfell

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3 Comments

Sam Over a year ago

I agree. The NPE is thrown later, probably when the author tries to loop through allNews but the last item is still null.

droidchef Over a year ago

Yes this code works, but i still didn't understand the flaw in my code, because the same code that i use works somewhere else perfectly in my app. then why not here?

superfell Over a year ago

if you have the same while(!last) construct, then its wrong elsewhere as well, perhaps that case doesn't hit the later NPE and so you haven't noticed.

kosa · Accepted Answer · 2013-01-16 20:56:31Z

1

while (!(cursor.isLast()))

I think issue while not of isLast(). You are explicitly saying if not last row.

Change while loop to:

 while (cursor.moveToNext()) {
   //Your code.
}

answered Jan 16, 2013 at 20:56

kosa

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