随机数字组成密码

private static Random random = new Random();     public static String getRandomNumber(String[] range,int rangeLength,int length){     StringBuffer sb = new StringBuffer();       for(int i=0;i<length;i++){            sb.append(String.valueOf(range[random.nextInt(rangeLength)]));        }         return sb.toString();     }    public static void main(String[] args) {       String[] range = {"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f","g","A","B","C"};       System.out.println(getRandomNumber(range, 20, 6));    }