I/O流类库提供对象之间的数据交互服务 输出流：表示数据从内存传送到某个载体或设备中； 输入流：数据从某个载体或设备传送到内存缓冲区变量中。-I/O stream class library to provide data exchange services between the object output stream: said data transfer from memory to a vehicle or equipment input stream: data fro