NullPointerException when assigning string from ArrayList to Java Array

Question

I have a problem with my code, because it throws NullPointerException when I try to assign string from arraylist to array.

 String[][] data = new String[idList.size()][];
 for(int i = 1; i<=idList.size(); i++) {
     data[i][0] = idList.get(i);
     data[i][1] = nameList.get(i);
     data[i][2] = hList.get(i);
     data[i][3] = sList.get(i);
     data[i][4] = fList.get(i);
     data[i][5] = mList.get(i);
     data[i][6] = osList.get(i);
     data[i][7] = tsList.get(i);
     data[i][8] = podList.get(i);
     data[i][9] = pacList.get(i);
 }

Can someone please tell me how do I fix that?

In your debugger you will be able to see that data[0] is null. I suggest you initialise them. — Peter Lawrey
– Peter Lawrey, Commented Apr 10, 2016 at 8:46

Eran · Accepted Answer · 2016-04-10 08:45:04Z

1

data[i] is null, since you initialized data to contain idList.size() null references of type String[].

Change

String[][] data = new String[idList.size()][];

to

String[][] data = new String[idList.size()][10];

which will initialize data to contain idList.size() references to a String array of length 10 (String[10]).

answered Apr 10, 2016 at 8:45

Eran

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Comments

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

I suggest to define the array properly (in both dimensions )

replace this

new String[idList.size()][];

for something like

new String[idList.size()][10]; // you have 10 different lists there...

and iterate in the for loop with zero base...

Example:

    String[][] data = new String[idList.size()][10];
    for (int i = 0; i < idList.size(); i++) {
        data[i][0] = idList.get(i);
        data[i][1] = idList.get(i);
        data[i][2] = idList.get(i);
        data[i][3] = idList.get(i);
    }

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Apr 10, 2016 at 8:50

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