Java read text and manipulate text data as integer

Question

i'm trying to read a csv file like this:

0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0,
0, 1, 2, 1, 0, 0, 1, 0,
1, 1, 0, 0, 10, 0,
0, 0, 0, 0, 0, 1, 1, 2, 1, 0,
0, 0, 0, 1, 0, 0, 0,

and convert into integer format and sum up for each row, but dunno why it's got error, my expected outcome should be like this:

[exam 1][LWD 5]
[exam 2][LWD 5]
[exam 3][LWD 12]
[exam 4][LWD 5]
[exam 5][LWD 1]

this is my java coding and i was using CSVReader library:

public static void main(String[] args) throws IOException {
    //read text file
    CSVReader a = new CSVReader(new FileReader("test.txt"));
    //store text data into arraylist
    List<String[]> aa = a.readAll();
    //create 2D array LWD
    int LWD[][] = new int[aa.size()][2];
    //store data to array LWD
    for (int i = 0; i < aa.size(); i++) {
        for (int x = 0; x < aa.get(i).length; x++) {
            LWD[i][1] += Integer.parseInt(aa.get(i)[x].trim());
        }
        LWD[i][0] = i+1;
    }
    //display LWD
    for (int i = 0; i < aa.size(); i++) {
    System.out.print("[exam " + LWD[i][0] + "]");
    System.out.print("[LWD " + LWD[i][1] + "]");
    System.out.print("\n");
    }
}

this is the error result i get:

Exception in thread "main" java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:504)
    at java.lang.Integer.parseInt(Integer.java:527)
    at test.Test.main(Test.java:20)
Java Result: 1

Answer 1

The issue appears to be that CSVReader is giving an empty string at the end of each line because of the trailing commas.

For example, when I run your exact code, but remove the trailing commas from the csv file like this:

0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0
0, 1, 2, 1, 0, 0, 1, 0
1, 1, 0, 0, 10, 0
0, 0, 0, 0, 0, 1, 1, 2, 1, 0
0, 0, 0, 1, 0, 0, 0

It gives the proper output.

I suppose you could either account for this by skipping the last String in each of the String arrays or changing the csv file(s)

Edit:
Here's a quick fix that should work with the current csv format:

public static void main(String[] args) throws IOException {
    //read text file
    CSVReader a = new CSVReader(new FileReader("test.txt"));
    //store text data into arraylist
    List<String[]> aa = a.readAll();
    //create 2D array LWD
    int LWD[][] = new int[aa.size()][2];
    //store data to array LWD
    for (int i = 0; i < aa.size(); i++) {
        for (int x = 0; x < aa.get(i).length-1; x++) {
            LWD[i][1] += Integer.parseInt(aa.get(i)[x].trim());
        }
        LWD[i][0] = i+1;
    }
    //display LWD
    for (int i = 0; i < aa.size(); i++) {
        System.out.print("[exam " + LWD[i][0] + "]");
        System.out.print("[LWD " + LWD[i][1] + "]");
        System.out.print("\n");
    }
}

All I changed was line 10, for (int x = 0; x < aa.get(i).length-1; x++) Changed x < aa.get(i).length to x < aa.get(i).length - 1 It might be more elegant to check if the string is empty instead, you might want to do that depending on the rest of the csv files.