IO流
def: 字节流：InputStream、OutputStream 字符流：Reader、Writer
FileOutputStream(pathname，true) true为追加
writer，自动创建文件，覆盖写入
FileInputStream
read
BufferedWriter 写入单个字符、字符数组及字符串
write
newLine
close
BufferedReader 读取单个字符、字符数组及一行字符
