Using parseInt to convert String to Integer returns NPE

Question

I am trying to convert a String to an Integer using the Integer.parseInt() method as follows:

public Job[] convertStringListToIntegerList(
            Integer noOfJobs, List<String> numbersListAsStrings) {
        Job[] integerList = new Job[noOfJobs];
        int i = 0;
        for (String s : numbersListAsStrings) {
            String[] jobWeightLength = s.split(" ");
            integerList[i].weight = Integer.parseInt(jobWeightLength[0]);
            integerList[i].length = Integer.parseInt(jobWeightLength[1]);
            i++;
        }
        return integerList;
    }

Here Job is defined as follows:

public class Job {
    Integer length;
    Integer weight;
    Integer difference;
    Float ratio;
}

I have referred to this question:

How to convert int[] to List in Java?

However, as you can see the variable I am using to store the result of Integer.parseInt() is an Integer, not an int and yet getting a NullPointerException at:

integerList[i].weight = Integer.parseInt(jobWeightLength[0]);

Can you please point me as to what's going wrong here?

I never thought enhanced for loops would result in index counters. Note that this method will fail is your list is bigger than noOfJobs. — Hannes, Jul 05 '14 at 12:12
@Hannes: I am pretty sure that the length of the list is equal to `noOfJobs`. However, is there a better method to make sure the method does not fail even if this is violated? — jobin, Jul 05 '14 at 12:16
You can use `int length = Math.min(noOfJobs, numbersListAsString);` to be sure, then use the determined length to size the job array and iterate through the list i = 0; i < length. — Hannes, Jul 05 '14 at 20:26

score 2 · Accepted Answer · answered Jul 05 '14 at 10:27

2

You need to create an instance of the Job class before you can assign to its fields

    for (String s : numbersListAsStrings) {
        String[] jobWeightLength = s.split(" ");
        integerList[i] = new Job();
        // ...

answered Jul 05 '14 at 10:27

Ian Roberts

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I am creating an array of `Job` here: `Job[] integerList = new Job[noOfJobs];`. Isn't that enough? – jobin Jul 05 '14 at 10:28
@Jobin No, arrays are __initialized__ with `null` references. – Unihedron Jul 05 '14 at 10:29
@Jobin `new Job[noOfJobs]` creates the array but all it's elements will be null - you have to create the individual Job instances separately. – Ian Roberts Jul 05 '14 at 10:31
Thanks! I am beginner and this was frustrating. Thanks for saving my day! :) – jobin Jul 05 '14 at 10:34

score 2 · Answer 2 · answered Jul 05 '14 at 10:28

2

Try following loop instead the one you have.

for (String s : numbersListAsStrings) {
        String[] jobWeightLength = s.split(" ");
        integerList[i]=new Job();
        integerList[i].weight = Integer.parseInt(jobWeightLength[0]);
        integerList[i].length = Integer.parseInt(jobWeightLength[1]);
        i++;
    }

This should solve your problem.

answered Jul 05 '14 at 10:28

Darshan Lila

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Thanks! @IanRoberts answered a little earlier, +1 though- this was exactly what was wrong. – jobin Jul 05 '14 at 10:34

score 1 · Answer 3 · answered Jul 05 '14 at 10:27

1

integerList[i] is null. integerList[i].weight references the weight field of a null Job. You should fill integerList with new Job() objects before using it.

see:

for (int i = 0; i < noOfJobs; i++)
    integerList[i] = new Job();

answered Jul 05 '14 at 10:27

Unihedron

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Thanks, @IanRoberts answered a little earlier, +1 though, this was exactly what was wrong. :) – jobin Jul 05 '14 at 10:35

score 0 · Answer 4 · answered Jul 05 '14 at 20:31

public Job[] convertStringListToIntegerList(
        Integer noOfJobs, List<String> numbersListAsStrings) {
    int size = Math.min(noOfJobs, numbersListAsStrings.length());
    Job[] integerList = new Job[size];

    for (int i = 0; i < size; i++) {
        String[] jobWeightLength = numbersListAsStrings.get(i).split(" ");
        integerList[i] = new Job();
        integerList[i].weight = Integer.parseInt(jobWeightLength[0]);
        integerList[i].length = Integer.parseInt(jobWeightLength[1]);
    }
    return integerList;
}

Using parseInt to convert String to Integer returns NPE

4 Answers4