What's the best way to build a string of delimited items in Java?

algorithm, java, string

Solution

Pre Java 8:

Apache's commons lang is your friend here - it provides a join method very similar to the one you refer to in Ruby:

`StringUtils.join(java.lang.Iterable,char)`

Java 8:

Java 8 provides joining out of the box via `StringJoiner` and `String.join()`. The snippets below show how you can use them:

`StringJoiner`

StringJoiner joiner = new StringJoiner(",");
joiner.add("01").add("02").add("03");
String joinedString = joiner.toString(); // "01,02,03"

`String.join(CharSequence delimiter, CharSequence... elements))`

String joinedString = String.join(" - ", "04", "05", "06"); // "04 - 05 - 06"

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

List<String> strings = new LinkedList<>();
strings.add("Java");strings.add("is");
strings.add("cool");
String message = String.join(" ", strings);
//message returned is: "Java is cool"

Problem

While working in a Java app, I recently needed to assemble a comma-delimited list of values to pass to another web service without knowing how many elements there would be in advance. The best I could come up with off the top of my head was something like this: ``` public String appendWithDelimiter( String original, String addition, String delimiter ) { if ( original.equals( "" ) ) { return addition; } else { return original + delimiter + addition; } } String parameterString = ""; if ( condition ) parameterString = appendWithDelimiter( parameterString, "elementName", "," ); if ( anotherCondition ) parameterString = appendWithDelimiter( parameterString, "anotherElementName", "," ); ``` I realize this isn't particularly efficient, since there are strings being created all over the place, but I was going for clarity more than optimization. In Ruby, I can do something like this instead, which feels much more elegant: ``` parameterArray = []; parameterArray << "elementName" if condition; parameterArray << "anotherElementName" if anotherCondition; parameterString = parameterArray.join(","); ``` But since Java lacks a join command, I couldn't figure out anything equivalent. So, what's the best way to do this in Java?

Original source