Question

I am having an issue with a String array and trying to add it to a list (List).
Below is the code that is used and creating the issue.

The program fails on the first run through of the loop and I have verified the input which comes from a CSV using OpenCSV.

List<String[]> output = null;
String[] temp;

for(int i = 0; i < 13; i++)
{               
    temp = reader.readNext();                           //read next line into temp
    System.out.println(temp[0]+temp[1]+temp[2]);        //temp output
    temp[2] = String.valueOf((values[i])/100);          //assign new value
    System.out.println(temp[0]+temp[1]+temp[2]);        //temp output
    output.add(temp);
}

When this code runs the output is.

VANCBULLET0.311
VANCBULLET0.308
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Main.updateCSV(Main.java:951)
    at Main.start(Main.java:863)
    at Main.access$23(Main.java:853)
    at Main$23.actionPerformed(Main.java:520)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)

The first two lines are correct and are split up like:
temp[0] temp[1] temp[2]
VANC BULLET 0.311
VANC BULLET 0.308

The issue is (like the error reads) at:

output.add(temp);

The documentation reads:

NullPointerException - if the specified element is null and this list does not permit null elements

but as you can see from my output (the second line) the array “temp” is not null, it contains “VANC BULLET 0.308” in each element respectively.

I’m stumped. Does anyone have an idea or see something I have failed to see?

Thanks

Answer 1

From what i can see you never initialized List<String[]> output = null; in your code. Thus when it call’s List.add as List is still null it throws NPE

initialize it first:

List<String[]> output = new ArrayList<String[]>();