1. Introduction

Converting an ArrayList to a CSV (Comma Separated Values) string in Java can be useful when we need to store or transfer data in a tabular format. In this guide, we will write a Java program that takes an ArrayList of ArrayLists and converts it to a CSV string.

2. Program Steps

1. Define a main method to serve as the entry point of the program.

2. Create an ArrayList of ArrayList of String, representing the rows and columns of data.

3. Initialize a StringBuilder to build the CSV string.

4. Iterate through the ArrayList and append each value to the StringBuilder, separating them by commas and ending each row with a newline character.

5. Convert the StringBuilder to a String and print the CSV string to the console.

3. Code Program

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class ArrayListToCSV {

    public static void main(String[] args) {

        // Step 2: Create an ArrayList of ArrayList of String
        List<List<String>> arrayList = new ArrayList<>();
        arrayList.add(Arrays.asList("Name", "Age", "Location"));
        arrayList.add(Arrays.asList("John", "30", "New York"));
        arrayList.add(Arrays.asList("Jane", "25", "Los Angeles"));
        arrayList.add(Arrays.asList("Mike", "35", "Chicago"));

        // Step 3: Initialize a StringBuilder
        StringBuilder csvBuilder = new StringBuilder();

        // Step 4: Iterate through the ArrayList and build the CSV string
        for (List<String> row : arrayList) {
            for (int i = 0; i < row.size(); i++) {
                csvBuilder.append(row.get(i));
                if (i < row.size() - 1) {
                    csvBuilder.append(",");
                }
            }
            csvBuilder.append("\n");
        }

        // Step 5: Convert the StringBuilder to a String and print the CSV string
        String csvString = csvBuilder.toString();
        System.out.print(csvString);
    }
}

Output:

Name,Age,Location
John,30,New York
Jane,25,Los Angeles
Mike,35,Chicago

4. Step By Step Explanation

– Step 1: The main method is defined as the entry point of the program.

– Step 2: An ArrayList of ArrayLists of Strings arrayList is created, representing the rows and columns of data.

– Step 3: A StringBuilder named csvBuilder is initialized to build the CSV string.

– Step 4: The program iterates through each row of the arrayList, appending each value to csvBuilder, separating them by commas, and ending each row with a newline character.

– Step 5: The csvBuilder is then converted to a String csvString, and printed to the console, showing the converted CSV string.

This Java program effectively demonstrates how to convert an ArrayList of ArrayLists into a CSV formatted string.