coding bat while loops

1)Given a string and a non-negative int n, return a larger string that is n copies of the original string.

public String stringTimes(String str, int n) {
  String f = "";
  while(n > 0){
      f += str;
      n--;
  }
  return f;
}


2)Given a string and a non-negative int n, we'll say that the front of the string is the first 3 chars, or whatever is there if the string is less than length 3. Return n copies of the front;

public String frontTimes(String str, int n) {
  String f = "";
  if (str.length() > 3){
    while(n > 0){
      f += str.substring(0,3);
      n--;
    }
  }else {
    while(n > 0){
      f += str;
      n--;
    }
  }
  return f;
}

3)Count the number of "xx" in the given string. We'll say that overlapping is allowed, so "xxx" contains 2 "xx"

int countXX(String str) {
  int xx = 0;
  int y = 0;
  while(y <= str.length()-2){
     if("xx".equals(str.substring(y,y+2))){
     xx += 1;
     }
     y++;
  }
  return xx;
}