Use of Substring

Ques: 

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"

Answer:

public String frontBack(String str) {

return(str.length()>1?(str.substring(str.length()-1,str.length())+str.substring(1,str.length()-1)+str.substring(0, 1)):str);

   }