将String数组转换为Int数组时发生NullPointerException

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));

Answer 1

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();
     }; 
   }
}

Answer 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) {}; 
}