字节流
字节流的父类(抽象类)
//InputStream 字节输入流 常用方法
public int read(){}
public int read(byte[] b){}
public int read(byte[] b, int off, int len){}
// OutputStream 字节输出流 常用方法
public void write(int n){}
public void write(byte[] b){}
public void write(byte[] b, int off, int len){}