NullPointerException at conversion of String array to Int array

Question

I am a beginner in programming and decided to make my own binary to decimal converter program for the fun of it. In my program, I move the String array's content to the Int array. the problem is that I seem to keep getting a NullPointerException error at the code where I change the String to Int. I have read the error and tried a lot of different methods to get rid of that error, but nothing helps. What could I be doing wrong?

"Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException"

My code:

int ans = 0;
int multi = 0;
strArray = null;
intArray = null;
if (rbBin.isSelected()) {
    txaNew.setText("");
    String num = ftxfOld.getText();
    strArray = num.replaceAll("\\[", "").replaceAll("\\]", "").split(",");

    for (int i = 0; i < strArray.length; i++) {
        try {
            intArray[i] = Integer.parseInt(strArray[i]); //I GET THE ERROR HERE
        } catch (NumberFormatException nfe) {
        }
    }
    for (int j = 0; j < num.length() + 1; j++) {
        multi = intArray[j] * 2 ^ j;
        ans = ans + multi;
    }
}
txaNew.append(Integer.toString(ans));

I think you need to make sure that the num value is formatted like this [1,2,3] and also could you print out the strArray value after you splitter the num variable? — kucing_terbang
– kucing_terbang, Commented May 9, 2015 at 15:37
Well, it looks like I found one of my problems. the number was not split into strArray. It was only placed into it, so it only has one spot and contains the entire number. Really did not think about testing that first :'( Thanks Sasha and kucing. Is there any way to split a normal number like "100" into an array like [1,0,0]? Or should I open another question for that? (I am new here) — Fieryfox
– Fieryfox, Commented May 10, 2015 at 11:59

Gabriele Mariotti · Accepted Answer · 2015-05-09 15:43:13Z

4

This happens because in java you have to initialize a variabile before using it. In your case when you do it:

intArray[i] = Integer.parseInt(strArray[i]); //I GET THE ERROR HERE

the initArray is null.

Change your code:

strArray = num.replaceAll("\\[", "").replaceAll("\\]", "").split(",");

if (strArray != null){
   //You have to initialize your variable
   intArray = new int[strArray.length];

   for (int i = 0; i < strArray.length; i++) {
     try {
        intArray[i] = Integer.parseInt(strArray[i]);
     } catch (NumberFormatException nfe) {
          nfe.printStackTrace();
     }; 
   }
}

answered May 9, 2015 at 15:43

Gabriele Mariotti

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6 Comments

Tom Over a year ago

I don't think that the check for strArray != null is necessary here, because String#split won't return null.

Vinze Over a year ago

indeed, I think it should be if(strArray.length > 0)

Tom Over a year ago

@Vinze Even that is not necessary, because that array will always contain at least one element (the whole source string, if no split was applied).

Tom Over a year ago

@Vinze No worries, that happens sometimes :).

Gabriele Mariotti Over a year ago

@Vinze It is not important if the strArray is empty. In any case the for cycle will not give an npe.

|

Raphael Amoedo · Accepted Answer · 2015-05-09 15:38:11Z

2

You have to instantiate intArray first.

intArray = new int[strArray.length];

So you will have:

String num = ftxfOld.getText();
strArray = num.replaceAll("\\[", "").replaceAll("\\]", "").split(",");
intArray = new int[strArray.length];

for (int i = 0; i < strArray.length; i++) {
try {
  intArray[i] = Integer.parseInt(strArray[i]); //I GET THE ERROR HERE
 } catch (NumberFormatException nfe) {}; 
}

answered May 9, 2015 at 15:38

Raphael Amoedo

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