Given a string, return a new string where the first and last chars have been exchanged.

frontBack("code") → "eodc"
frontBack("a") → "a"
frontBack("ab") → "ba"

[FONT="Courier New"]public String frontBack(String str)
{
  String firstLetter = str.substring(0,1);
  String lastLetter = str.substring([B]str.length - 1[/B, str.length); //is that valid?..
}[/FONT]