allStar challenge

Hi,

I am working on below challenge.
http://codingbat.com/prob/p183394
Psedo code:
1. check the array length 0  or 1 then retun same str
2.else return string with first character concatenated with * and then rest of characters argument recursion method

I wrote my code as below and passing all tests

public String allStar(String str) {
  if(str.length()==0||str.length()==1){
    return str;
  }
  else{
  return str.charAt(0)+"*"+allStar(str.substring(1));
  }
}

Any improvements or alternate approaches?      

please advise