字符缓冲流

BufferedReader和BufferedWriter
二者有特有方法：
BufferedReader String readLine() 读一行文字
BufferedWriter void newLine() 写一换行符

        try (BufferedReader bis = new BufferedReader(new FileReader("test.txt"));) {
            String s = null;
// 读到文件末尾后会返回null
            while ((s = bis.readLine()) != null) {
                System.out.println(s);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }