Apex Join

join.cls

String join(List<String> values) {
      List<String> valueCopy = new List<String>(values);
      if(valueCopy.isEmpty())
        return null;
      String result = valueCopy[0];
      valueCopy.remove(0);
      while(!valueCopy.isEmpty()) {
        result += ',' + valueCopy[0];
        valueCopy.remove(0);
      }
      return result;
}