code: public static String insert(String haystack, String needle, int index) {
  		StringBuffer val = new StringBuffer(haystack);
  		val.insert(index, needle);
  		return val.toString();
  	}
docs: replaces the first occurrence of needle in haystack with newNeedle
  
  @param haystack input string
  @param needle   string to place
  @param index	position to place