converting 2d string array to 2d integer array

Question

I keep on getting a null pointer exception and I have no idea why. Explain please.

public static int[][] convertStringToInt(String[][] array){

    int [][] numbers = new int [array.length][];
    for(int row = 0; row < array.length; row++)
    {
        numbers[row] = new int [array[row].length];                //line 48
        for(int col = 0; col < array[row].length; col++)
        {
            numbers[row][col] = Integer.parseInt(array[row][col]);
        }
    }
    return numbers;
}



public static void main (String[] agrs)
{

    File selectedFile = selectFile("Enter fileName for double number, EX:    
                      decimalNumbers.csv");
    if( !selectedFile.exists())
    {
       System.out.print("\nFile does not exit, program terminating\n\n");
       System.exit(1);
    }

    int countLines = countLinesInFile(selectedFile);
    String cities [][] = loadArrayFromFile(selectedFile, countLines);

    int [][] unitsSold = convertStringToInt(cities); //line 157

    System.out.println(unitsSold);
 }

here are the errors when i enter the file name

Exception in thread "main" java.lang.NullPointerException
at labReview.ArrayOfArrays.convertStringToInt(ArrayOfArrays.java:48)
at labReview.ArrayOfArrays.main(ArrayOfArrays.java:157)

This works fine for me, can you give an input example where the error occurs? — Christian Tapia
– Christian Tapia, Commented Jan 30, 2014 at 6:25
I don't understand this: int [][] numbers = new int [array.length][]; ... the second dimension isn't specified. — Chthonic Project
– Chthonic Project, Commented Jan 30, 2014 at 6:26
It's not necessary to specify second dimension in 2D arrays. Try googling it. — Christian Tapia
– Christian Tapia, Commented Jan 30, 2014 at 6:27
Try printing your cities variable before passing it to the converter. Or even better, debug. — Keppil
– Keppil, Commented Jan 30, 2014 at 6:28

Christian Tapia · Accepted Answer · 2014-01-30 06:29:42Z

1

The method convertStringToInt works fine. The exception you described NullPointerException may occur in the line

numbers[row] = new int[array[row].length];

if array[row] is null. So the error may be occuring because the method loadArrayFromFile is returning a null row, like this (for example):

String[][] s = { { "1", "2", "3" }, { "1" }, null, { "3", "4" } };

Print the elements in the array returned by the method loadArrayFromFile to see if there are null rows.

answered Jan 30, 2014 at 6:29

Christian Tapia

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Comments

Sharath Bhaskara · Accepted Answer · 2014-01-30 08:23:28Z

0

I guess, you have a null array in your cities at some index.

String cities [][] = loadArrayFromFile(selectedFile, countLines);

Try printing your cities array as below

for(String[] cityArr : cities){
 System.out.println("Cities at Index "+i+" is : "+citiArr);
}

And if you see a "null" value at any index, then modify your loadArrayFromFile to replace a black array whenever you have a null while adding it to cities array.

....

if(citiArr==null){
 citiArr = new String[]{};
}
cities[i][j]=citiArr;

....

answered Jan 30, 2014 at 8:23

Sharath Bhaskara

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