我试图使用readObject读取二进制文件中的行数，但得到IOException EOF。我这样做正确吗？

    FileInputStream istream = new FileInputStream(fileName);
    ObjectInputStream ois = new ObjectInputStream(istream);

    /** calculate number of items **/
    int line_count = 0;
    while( (String)ois.readObject() != null){            
        line_count++;
    }