reading a csv file into a array

arrays, csv, java

Solution

Although using the Apache CSV library as mentioned by @Minjun.Y is perfectly fine, I try to provide a solution that is closer to your code and maybe easier for you to follow:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class CsvParser {

    public static void main(String[] args) {
        String fileName= "read_ex.csv";
        File file= new File(fileName);

        // this gives you a 2-dimensional array of strings
        List<List<String>> lines = new ArrayList<>();
        Scanner inputStream;

        try{
            inputStream = new Scanner(file);

            while(inputStream.hasNext()){
                String line= inputStream.next();
                String[] values = line.split(",");
                // this adds the currently parsed line to the 2-dimensional string array
                lines.add(Arrays.asList(values));
            }

            inputStream.close();
        }catch (FileNotFoundException e) {
            e.printStackTrace();
        }

        // the following code lets you iterate through the 2-dimensional array
        int lineNo = 1;
        for(List<String> line: lines) {
            int columnNo = 1;
            for (String value: line) {
                System.out.println("Line " + lineNo + " Column " + columnNo + ": " + value);
                columnNo++;
            }
            lineNo++;
        }
    }

}

Let's go through it step-by-step:

I added 3 more imports: `ArrayList`, `Arrays` and `List` - you will see very soon for what they are good. They are all taken from the `java.util` library, a standard library that is available with every JDK.

Every class name in Java starts with a capital letter (by convention - it will build with a small letter as well, but you should get used to this convention) - I "fixed" this in your code.

I added a 2-dimensional array `List<List<String>> lines = new ArrayList<>()`. This might look a little confusing at first, but what it means is that we create a variable `lines` that holds the results of our parsing. The `List<String>` syntax means, that we have a generic type `List` that has a type parameter `String` - in other words: a list of strings. The whole `List<List<String>>` means we have a list of lists of strings, a 2-dimensional string array.

With the `lines.add(Arrays.asList(values))` in your `while` loop, we can add the lines that you parsed to this 2-dimensional array. `Arrays.asList(values)` transforms the `String[]` array into a `List` as we need it to be compatible to our `List<List<...>>` type. This allows your lines to have variable length.

The last lines I added simply print the content of 2-dimensional array and should give you a good example for how to access the values in this array. If you need further help for this construct, check the foreach loop documentation.

Given this as an input file (`read_ex.csv`):

value_1-1,value_1-2,value_1-3,value_1-4
value_2-1,value_2-2,value_2-3,value_2-4
value_3-1,value_3-2,value_3-3,value_3-4
value_4-1,value_4-2,value_4-3,value_4-4
value_5-1,value_5-2,value_5-3,value_5-4

The program will print the following output:

Line 1 Column 1: value_1-1
Line 1 Column 2: value_1-2
Line 1 Column 3: value_1-3
Line 1 Column 4: value_1-4
Line 2 Column 1: value_2-1
Line 2 Column 2: value_2-2
Line 2 Column 3: value_2-3
Line 2 Column 4: value_2-4
Line 3 Column 1: value_3-1
Line 3 Column 2: value_3-2
Line 3 Column 3: value_3-3
Line 3 Column 4: value_3-4
Line 4 Column 1: value_4-1
Line 4 Column 2: value_4-2
Line 4 Column 3: value_4-3
Line 4 Column 4: value_4-4
Line 5 Column 1: value_5-1
Line 5 Column 2: value_5-2
Line 5 Column 3: value_5-3
Line 5 Column 4: value_5-4

Hope this helps :)

Problem

Original source