Can't access last element of array

Question

I am parsing a .CSV file, line after line and i want to get the values of the columns. So as example for my .CSV file :

time;columnA;columnB,ColumnC
27-08-2013 14:43:00; this is a text; this too; same here

So what I did is store the content in an bidimensional String array (thanks to split()). My array is made as follow :

array[0][x] = "time".
array[y][x] = "27-08-2013 14:43:00";

they are x different columns, but the name of every column is only stored on line[0][x]. they are y different lines, with the value stored as String in it.

My problem is the following, I want to get the [x] position of the data, but when i try to access the last [x] element of the array. I receive this as error-message

java.lang.ArrayIndexOutOfBoundsException: 17
    at IOControl.ReadCsvFile.getPosVar(ReadCsvFile.java:22)
    at IOControl.ReadCsvFile.<init>(ReadCsvFile.java:121)
    at en.window.Main.main(Main.java:48)

Obviously i'm reading to far, but how?

Here my code :

//Retrieves the x position of the variable var given as parameter.
private int getPosVar(String[][] index, String var)
{
    int x = 0;
    boolean cond = false;
    while((index[0][x] != null) && (cond != true))
    {
        if (index[0][x].contains(var) == true)
        {
            cond = true;
        }
        x++;
    }
    System.out.println("x = " +x+ "  val = " +index[0][x]);
    return(x);
}

I thought it may be because I didn't checked that my x value was smaller than the full string. like this :

x < index[x].length

But in fact I didn't changed anything, and when I give an unknown String var it also goes too far. Why?

Answer 1

Checking the validity of index before using it is also a good idea:

if ( index == null || index.length == 0 ) return -1;

Your while loop should look more like this:

while ( x < index[0].length )
{
    if ( index[0][x] == null )
    {
        x++;
        continue; // skip possible null entries.
    }

    if ( index[0][x].contains(var) )
    {
        System.out.println("x = " + x + ", val = " + index[0][x]);
        return x; // return the position found.
    }
    x++;
}
return -1;

Using a for loop (which I prefer):

for ( int x = 0; x < index[0].length; x++ )
{
    if ( index[0][x] == null )
        continue; // skip possible null entries.

    if ( index[0][x].contains(var) )
    {
        System.out.println("x = " + x + ", val = " + index[0][x]);
        return x; // return the position found.
    }
}

Answer 2

x < index[x].length

The issue is not the length of index[x], but that x is too large. You need to check:

index.length < x

Answer 3

you should check against

x < index[0].length

and it would be good to check

index != null && index.length > 0

before accessing index at all.

After you found a correct result your code also increments "x++" so x is moving one element further. If you now find the last Element or / no Element then this will manage to overflow the array bounds, thus

System.out.println("x = " +x+ "  val = " +index[0][x]);

will throw an error.

I would suggest to change it like this:

private int getPosVar(String[][] index, String var)
{
    int x = 0;
    boolean found = false;

    if(index == null || index.length == 0 || var == null)
        return -1;

    while((x < index[0].length))
    {
        if (index[0][x].contains(var))
        {
            System.out.println("x = " +x+ "  val = " +index[0][x]);
            return(x);
        }
        x++;
    }
    System.out.println("  var = " + var + " not found");
    return -1;
}

Answer 4

You're ignoring array bounds completely. Where do you make sure in your while loop that your x variable isn't too big? Nowhere.

Answer 5

At the end of the while loop you increase the value of x. Afterwards you try to get the value again in the sysout method.

EDIT: Try to put the x++ in an else block.

Answer 6

Becase you are incrementing the value after you do the check. Which leads to the next check being too much. You can solve this simply by adding a brake statement like this.

    public static void main(String[] args) {
    String var = "c";
    String[][] index = {{"a","b","c"},{"a","b","c"}};
    int x = 0;
    boolean cond = false;
    while( (index[0][x] != null) && (cond != true) )
    {
        if (index[0][x].contains(var) == true)
        {
            cond = true;
            break;
        }
        x++;
    }
    System.out.println("x = " +x+ "  val = " +index[0][x]);

Also you should always try to use a forloop instead of a while loop they make it much harder to get errors like these if you check for the length of an array.

Answer 7

You can use your old program

public class TwoDStringArray {

static String[][] index = new String[1][3];

public static void main(String[] args) {

    index[0][0] = "amal";
    index[0][1] = "dev";

    int x = 0;
    boolean cond = false;
    String var = "dev";
    while((index[0][x] != null) && (cond != true))
    {

        if (index[0][x++].equals(var) == true)
        {
            cond = true;
            x--;
        }
    }

    System.out.println("x = " +x+ "  val = " +index[0][x] + "    "+ cond);
}

}

O/P ---->>>

x = 1 val = dev true

---

but you have to notice one thing when you declare static String[][] index = new String[1][3];

here compiler initialize the 'index' with index[0][0]=null , index[0][1]=null , index[0][2]=null

but there is no index[0][3]

so it will show ArrayIndexOutOfBoundsException

so do one thing if there are 'n' elements in your program then declare 'index' like this

static String[][] index = new String[1][n+1];