Java - Append quotes to strings in an array and join strings in an array

Question

I would like to append double quotes to strings in an array and then later join them as a single string (retaining the quotes). Is there any String library which does this? I have tried Apache commons StringUtils.join and the Joiner class in Google guava but couldn't find anything that appends double quotes.

My input would be an array as mentioned below:

String [] listOfStrings = {"day", "campaign", "imps", "conversions"};

Required output should be as mentioned below:

String output = "\"day\", \"campaign\", \"imps\", \"conversions\"";

I know I can loop through the array and append quotes. But I would like a more cleaner solution if there is one.

Answer 1

With Java 8+

Java 8 has Collectors.joining() and its overloads. It also has String.join.

Using a Stream and a Collector

The naive but effective way

String wrapWithQuotesAndJoin(List<String> strings) {   return strings.stream()     .map(s -> "\"" + s + "\"")     .collect(Collectors.joining(", ")); } 

Shortest and probably better performing (somewhat hackish, though)

String wrapWithQuotesAndJoin(List<String> strings) {   return strings.stream()     .collect(Collectors.joining("\", \"", "\"", "\"")); } 

Using String.join

Very hackish. Don't use. (but it must be mentioned)

String wrapWithQuotesAndJoin(List<String> strings) {   return strings.isEmpty() ? "" : "\"" + String.join("\", \"", strings) + "\"" } 

With older versions of Java

Do yourself a favor and use a library. Guava comes immediately to mind.

Using Guava

private static final Function<String,String> addQuotes = new Function<String,String>() {   @Override public String apply(String s) {     return new StringBuilder(s.length()+2).append('"').append(s).append('"').toString();   } }; String wrapWithQuotesAndJoin(List<String> strings) {          return Joiner.on(", ").join(Iterables.transform(listOfStrings, addQuotes)); } 

No libraries

String wrapWithQuotesAndJoin(List<String> strings) {   if (listOfStrings.isEmpty()) {     return "";   }   StringBuilder sb = new StringBuilder();   Iterator<String> it = listOfStrings.iterator();   sb.append('"').append(it.next()).append('"'); // Not empty   while (it.hasNext()) {     sb.append(", \"").append(it.next()).append('"');   }   result = sb.toString(); } 

Notes:

• All the solutions assume that strings is a List<String> rather than a String[]. You can convert a String[] into a List<String> using Arrays.asList(strings). You can get a Stream<String> directly from a String[] using Arrays.stream(strings).
• The Java 8+ snippets use the + concatenation because at this point + is usually better performing than StringBuilder.
• The older-version snippets use StringBuilder rather than + because it's usually faster on the older versions.

Answer 2

String output = "\"" + StringUtils.join(listOfStrings , "\",\"") + "\"";