文件的学习：
都是在java.io这个文件夹的包下面
1.文件类：File

1.字节输出流-InputStream-  1.FileInputStream
      2.FilterInputStream过滤流
        BufferInputStream
        DataInputStream
2.字节输入流-OutputStream- 1.FileOuetStream
      2.FilterOnputStream过滤流
        BufferOutputStream
        DataOutputStream数据流

1.字符流：Reader  InputStreamReader-FileReader
    BufferedReader
2.  Writer  OutputStreamReader-FileWriter
    BufferedWriter