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

To join array elements with a separator in Java, you can use the join method from the String class. This method was introduced in Java 8 and it allows you to join the elements of an array or an Iterable object with a specified delimiter:

String[] elements = {"a", "b", "c"};
String result = String.join(",", elements);  // "a,b,c"

If you are using an older version of Java that does not have the join method, you can use a StringBuilder to concatenate the elements with the separator:

String[] elements = {"a", "b", "c"};
StringBuilder sb = new StringBuilder();
for (int i = 0; i < elements.length; i++) {
    if (i < elements.length - 1) {
String result = sb.toString();  // "a,b,c"

You can also use the Collectors.joining method from the java.util.stream.Collectors class to join the elements of a stream:

String[] elements = {"a", "b", "c"};
String result = Arrays.stream(elements).collect(Collectors.joining(","));  // "a,b,c"

This is useful if you want to join the elements of a stream in a functional style.