Csv.java

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Scanner;

class TooFewColumnsException extends Exception {
    public TooFewColumnsException(int row) {
        super("Error reading CSV file at row " + row + ": too few columns");
    }
}

public class Csv {
    public static void main(String[] args) {
        try {
            readCSV("test.csv");
        } catch (FileNotFoundException e) {
            System.out.println("File not found");
        } catch (TooFewColumnsException e) {
            System.out.println(e.getMessage());
        }
    }

    public static void readCSV(String filename)
        throws FileNotFoundException, TooFewColumnsException {
        try (Scanner scanner = new Scanner(new FileReader(filename))) {
            String header = scanner.nextLine();
            int columns = header.split(",").length;

            int rowNum = 0;
            while (scanner.hasNextLine()) {
                ++rowNum;
                String row = scanner.nextLine();
                if (row.split(",").length != columns) {
                    throw new TooFewColumnsException(rowNum);
                }
            }
        }
    }
}