How to Join a List of Strings By a Delimiter in Java

Published Dec 24, 2021  ∙  Updated Jun 27, 2022

Suppose we have an ArrayList, and we want to join all the elements together by some character, or delimiter.

List<String> list = Arrays.asList("a","b","c");

Let’s say we want to join these elements with commas to create the string: a,b,c.

1. Join a list using String.join()

We can easily use String.join() to concatenate multiple strings by a delimiter, which is specified in the first parameter.

String res = String.join(",", list);

2. Join a list using the Stream API

We can use the Stream API’s Collectors.joining() method to achieve the same functionality.

String res = list.stream().collect(Collectors.joining(","));

3. Join a list using StringJoiner

The third option is to scrap the list entirely.

If we know that all we want to do is join the elements into a string, then we can use StringJoiner from the get-go.

StringJoiner joiner = new StringJoiner(",");
joiner.add("a");
joiner.add("b");
joiner.add("c");
String res = joiner.toString();