Null Pointer Exception in an Array of Strings

Question

I am creating a shadow of createTriangle() in the method createPathingTriangle(). createTriangle worked just fine, but when I created the identically-dimensioned createPathingTriangle that used String instead of int, the new triangle started throwing NPE's.

The line that's throwing it is-

pathingTriangle[y][x] = new String("00" + String.valueOf(x));

i.e. the first line that populates it. I looked it up and have liberally sprinkled "new" around the code in createPathingTriangle, but it didn't seem to solve the problem.. I am assuming that it has something to do with the fact that int is a primitive but String is not, but hours of fiddling and nothing gives.

private int[][] createTriangle() {
    triangle = new int[triangleSize][];
    for (int y = 0; y < triangle.length; y++){
        int [] xAxis = new int[triangle.length - y];
        for (int x = 0; x < xAxis.length; x++){
            xAxis[x] = (int) (Math.random() * 100);
        }
        triangle[y] = xAxis;
    }
    printTriangle(triangle);
    return triangle;
}

private String[][] createPathingTriangle() {
    pathingTriangle = new String[triangleSize][];

    for (int y = 0; y < pathingTriangle.length; y++){
        for (int x = 0; x < pathingTriangle.length - y; x++){
            if (x < 10){
                pathingTriangle[y][x] = new String("00" + String.valueOf(x));
            }
            else if (x < 100){
                pathingTriangle[y][x] = new String("0" + String.valueOf(x));
            }
            else{
                pathingTriangle[y][x] = new String(String.valueOf(x));
            }
        }
    }
    return pathingTriangle;
}

First of all don't use new String(); as you create new String objects unnecessarily. Second can you provide some stack trace and more information — Eypros
– Eypros, Commented Aug 29, 2014 at 8:42
The code is not the same for String and int, in the int code, you are correctly creating int arrays (int [] xAxis = new int[triangle.length - y];), and using them, but not in the String code. — Florent Bayle
– Florent Bayle, Commented Aug 29, 2014 at 8:42

Jens · Accepted Answer · 2014-08-29 08:43:07Z

3

You never initialize the second dimension of the array pathingTriangle = new String[triangleSize][];

which is done in the first funnction here int [] xAxis = new int[triangle.length - y];

answered Aug 29, 2014 at 8:43

Jens

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1 Comment

stravinsky7 Over a year ago

Thanks for your help. I reverted the code back to that, and it all worked out somehow. What's weird is that I had originally just copied and pasted the code, and replaced int with String and it didn't just work from the get-go.

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