我写的Java学生成绩管理系统源代码

                        new InputStreamReader(System.in));    //收数    
                String inputLine = in.readLine();             //据
                StringTokenizer str =                                          
                    new StringTokenizer(inputLine," ");//接收的数据用空格隔开,这个类用来提取每个字符串                         
                long num = Integer.valueOf(str.nextToken()).longValue();//学号          
                String name = (String)str.nextToken();                  //姓名
                String sex = (String)str.nextToken();                   //性别
                double mark = Integer.valueOf(str.nextToken()).doubleValue();//分数
                all = String.valueOf(num) +" , "+
                name +" , "+
                sex +" , "+
                String.valueOf(mark);//把所有的数据用" , "隔开然后在连起来放进字符串all           
        }catch (IOException e){}
         catch (NumberFormatException e){}
        return all;//返回字符串all
    }
    public void addData(String str)//增加数据的方法
    throws IOException
    {
        String s1 ="",s2="" ,s3= "";
        File file = new File("data.txt");