Asking for help and downvoting my comment at the same time...? Weirdest thing of the day, I bet...

1. search for simpler ways. Find a way to "mutate a string" in java (yes, String are immutable. But that's an hint)
2. there are no outputs of this length. If that happens with your code, you didn't understand the task correctly.

It's 2 kyu, I won't give you the answer straight away (especially considering that it's a really basic knowledge that you seem to be missing)

There are dedicated tools/objects in Java for this type of stuff, just use them. ;)