Java Join String[] Example

Let’s see the example of joining array of String to produce single String. We may need this information many times during development specially while parsing contents out of JSON or XML.

1) Join String Array using String.join() method – Java 8

String.join() method has two flavors.

i) join(CharSequence delimiter, CharSequence… elements)

This method can be used to join multiple strings which are noy yet in form of collection or array.

String joinedString = String.join(", ", "How", "To", "Do", "In", "Java");
System.out.println(joinedString);

Output:

How, To, Do, In, Java

ii) join(CharSequence delimiter, Iterable elements)

This method is used to join array or list of strings.

List<String> strList = Arrays.asList("How", "To", "Do", "In", "Java");
		
String joinedString = String.join(", ", strList);
System.out.println(joinedString);

Output:

How, To, Do, In, Java

or

String[] strArray = { "How", "To", "Do", "In", "Java" };
		
String joinedString = String.join(", ", strArray);
System.out.println(joinedString);

Output:

How, To, Do, In, Java

2) Using StringJoiner for formatted output

Using StringJoiner, you can produce formatted output of joined string. This is specially useful while using lambda collectors.

It’s constructor takes three arguments – delimiter [mandatory], and optionally prefix and suffix.

StringJoiner(CharSequence delimiter)
StringJoiner(CharSequence delimiter, CharSequence prefix, CharSequence suffix)

If with similar input as above example, you want to format the output as [How, To, Do, In, Java], then you can below code:

StringJoiner joiner = new StringJoiner(", ", "[", "]");
joiner.add("How").add("To").add("Do").add("In").add("Java");

Output:

[How, To, Do, In, Java]

While using lambda, you can use Collectors.joining() in similar way.

List<String> numbers = Arrays.asList("How", "To", "Do", "In", "Java");
String joinedString = 	numbers
						.stream()
						.collect(Collectors.joining(", ","[","]"));

System.out.println(joinedString);

Output:

[How, To, Do, In, Java]

3) Join String Array using StringUtils.join() method – Apache Commons Lang

The StringUtils class of the Commons Langs library has several join() methods that can be used to combine an array or collection of strings into a single string.

String[] strArray = { "How", "To", "Do", "In", "Java" };

String joinedString = StringUtils.join(strArray);
System.out.println(joinedString);

String joinedString2 = StringUtils.join(strArray, ", ");
System.out.println(joinedString2);

Output:

HowToDoInJava
How, To, Do, In, Java

Happy Learning !!

Reference(s):

Java 8 String Doc
StringJoiner Java Doc
Apache Commons StringUtils Doc