I/O相关 输入/输出 流（数据流动）
都在java.io包下

按数据流动的方向 分两类
读数据（输入input）
写数据（输出output）
比如 文件流 缓冲流 *对象流 字符串流 数据流 网络流….

数组流
byte数组 ByteArrayInputStream ByteArrayOutputStream
char数组 CharArrayReader CharArrayWriter

数据流 DataInputStream DataOutputStream

字符流

Reader
BufferedReader
InputStreamReader
FileReader
StringReader
PipedReader
CharArrayReader
FilterReader
PushbackReader
Writer
BufferedWriter
OutputStreamWriter
FileWriter
PrinterWriter
StringWriter
PipedWriter
CharArrayWriter
FilterWriter

字节流

InputStream
FileInputStream
FilterInputStream
BufferedInputStream
DataInputStream
PushbackInputStream
ObjectInputStream
PipedInputStream
SequenceInputStream
StringBufferInputStream
ByteArrayInputStream
OutputStream
FileOutputStream
FilterOutputStream
BufferedOutputStream
DataOutputStream
PrintOutputStream
ObjectOutputStream
PipedOutputStream
ByteArrayOutputStream