The java.io package contains classes to support reading and writing streams, files, and pipes. These classes form a fairly structured hierarchy -- most of them are subclasses of InputStream or OutputStream.
The java.net package contains classes to support network programming. These include dealing with sockets, Internet addresses, network datagrams, uniform resource locators (URLs), and content handlers for data from a URL. To name a few, the URL class provides a very simple interface to networking -- the object referred to by the URL can be downloaded with a single call, and the Socket class allows you to connect to a specified port on a specified Internet host and read and write data using the InputStream and OutputStream classes of the java.io package.