Approach 1: Using Collectors.joining()

List<String> parts = Arrays.asList("a", "b", "c");
String csv = parts.stream().collect(Collectors.joining(","));
System.out.println(csv); // a,b,c

Why it works:

• Collectors.joining(delimiter) concatenates strings with the given delimiter.

Approach 2: Using String.join() (Alternative)

String csv = String.join(",", parts);
System.out.println(csv); // a,b,c

Why it works:

• Simple and idiomatic for lists of strings.
• Does not require a stream.