Hey Tanuja!

Here's my take:

String input = "test/this/string";

List<String> list = Arrays.asList(input.split("(?=/)|(?<=/)"));

Collections.reverse(list);

StringBuilder sb = new StringBuilder();

for (String s: list)

   sb.append(s);

System.out.println(sb.toString());

(?<=/) is a zero-length matching regex that matches if the previous character is a /.
(?=/) is a zero-length matching regex that matches if the next character is a /.

So (?=/)|(?<=/) matches right before and after each /, thus the split splits the string into"test", "/", "this", "/", "string".