A quick and easy way to join array elements with a separator (the opposite of split) in Java

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I'm looking for a quick and easy way to do exactly the opposite of split

so that it will cause ["a","b","c"] to become "a,b,c"

Iterating through an array requires either adding a condition (if this is not the last element, add the seperator) or using substring to remove the last separator.

I'm sure there is a certified, efficient way to do it (Apache Commons?)

How do you prefer doing it in your projects?

Answer

Using Java 8 you can do this in a very clean way:

String.join(delimiter, elements);

This works in three ways:

1) directly specifying the elements

String joined1 = String.join(",", "a", "b", "c");

2) using arrays

String[] array = new String[] { "a", "b", "c" };
String joined2 = String.join(",", array);

3) using iterables

List list = Arrays.asList(array);
String joined3 = String.join(",", list);