Convert a List of String to a comma separated String in Java

Last Updated : 23 Jan, 2026

In Java, a List<String> can be efficiently converted into a comma-separated String using built-in utilities like String.join(), which concatenates list elements with a specified delimiter while ensuring clean, readable, and loop-free code.

Examples:

Input: List<String> = ["Geeks", "ForGeeks", "GeeksForGeeks"]
Output: "Geeks, For, Geeks"

Input: List<String> = ["G", "e", "e", "k", "s"]
Output: "G, e, e, k, s"

Syntax

String.join(CharSequence delimiter, Iterable<? extends CharSequence> elements)

  • delimiter: The string used to separate elements (, in this case)
  • elements: The list of strings to be joined
Java 
import java.util.*;
public class GFG {
    public static void main(String args[]) {
        List<String> list = new ArrayList<>(Arrays.asList("Geeks", "ForGeeks", "GeeksForGeeks"));
        System.out.println("List of String: " + list);
        String result = String.join(",", list);
        System.out.println("Comma separated String: " + result);
    }
}

Output
List of String: [Geeks, ForGeeks, GeeksForGeeks]
Comma separated String: Geeks,ForGeeks,GeeksForGeeks

Explanation:

  • String.join() combines all list elements into one string.
  • A comma (",") is inserted automatically between elements.
  • This approach avoids loops and makes the code clean and readable.
  • Time Complexity: O(N), where N is the number of elements in the list
  • Auxiliary Space: O(1) (excluding the output string)
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