Question

I am reading in a .csv file sort of like a spreadsheet in excel. There are a certain number of columns, determined by the file, and I read each line into a string array using the .split(",") method. I then put this into an array list so it can hold all of the string arrays without giving it a specific size. However, when I go to sort the array list using Collections.sort(), the program breaks. What could the problem be? Here is my code to sort:

Collections.sort(stringList, new Comparator < String[] > () {
    public int compare(String[] strings, String[] otherStrings) {
        return -1 * (strings[sortNum].compareTo(otherStrings[sortNum]));
    }
});

Answer 1

Two points:

• Don’t multiply the result of compare by -1 to reverse a comparison. Integer.MIN_VALUE * -1 is still Integer.MIN_VALUE. Instead, reverse the order of the comparison itself
• My guess is that you’ve actually got some rows without enough columns. Perhaps you should put those at the end?

Something like:

Collections.sort(stringList, new Comparator < String[] > () {
    public int compare(String[] x1, String[] x2) {
        if (x1.length > sortNum && x2.length > sortNum) {
            return x2[sortNum].compareTo(x1[sortNum]); 
        }
        if (x1.length > sortNum) {
            return 1;
        }
        if (x2.length > sortNum) {
            return -1;
        }
        return x2.length - x1.length;
    }
});

Alternatively, filter your list first to make absolutely sure that all rows have enough columns.