Description Klaus Reimer 2006-08-24 03:40:00 EDT

We found a situation in our code where the new Null-Pointer warning of Eclipse 3.2 gave a false-positive. In [1] Eclipse says that "e" can't be null. So we naivly removed the null pointer check and our application was no longer working. I have removed as much of the code as possible to find the root of the problem and ended up with this code:

    public void test(String p)
    {
        List<String> list = new ArrayList<String>();
        Iterator<String> it = list.iterator();

        while (it.hasNext())
        {
            String e = it.next();
            e.toString();

            while (true)
            {
                if (it.hasNext()) // [2]
                    e = it.next();
                else
                    e = null;

                if (e == null || p != null) // [3]
                {
                    if (e != null) // [1]
                    {
                        // Do something
                    }
                    break;
                }
            }
        }
    }

The code is total nonsense now but it demonstrates the problem. It is definetly possible that e is null in [1]. If no more elements are in the array when we reach [2] then e is set to null and the if statement in [3] resolves to true. When we trust in the warning then we remove the null pointer check [1] and end up with null-pointer exceptions because e can be null. That's exactly what caused the problem in our application after removing the null-pointer check to resolve the warning.

I'm not sure what confuses the parser here. If I remove the break, the warning is gone. If I remove one of the while loops, the warning is gone, too. Sorry, that I was not able to shorten the code more.