An internet is a collection of two or more distinct networks joined by routers, which have the task of translating one network's language to the other's. The Internet is a network of networks that uses the Internet Protocol (IP) as the translation medium.
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A protocol is a set of rules that controls the transfer of information between two computers in a network. The HyperText Transfer Protocol (HTTP) governs information exchange on the World Wide Web (WWW). The Simple Mail Transfer Protocol controls mail service on the Internet. The File Transfer Protocol (FTP) controls the transfer of files between Internet computers. The Domain Name System (DNS) governs the use of names on the Internet.
A client/server application is one that divides its task between a client, which requests service, and a server, which provides service. Many Internet applications and protocols are based on the client/server model.
Lower-level protocols, such as the ethernet protocol and token ring protocol, govern the transmission of data between computers on a single network. The Internet Protocol (IP) translates between such protocols.
A Uniform Resource Locator (URL) is a standard way of specifying addresses on the Internet. It consists of several parts separated by slashes and colons: method://host:port/path/file. The java.net.URL class is used to represent URLs.
Files of text or data (images, audio files) on the Internet or Web can be downloaded using the same InputStreams and OutputStreams as files located on a disk. To read or write a resource located on a network, you need to connect its URL to an input or output stream.
The java.awt.Toolkit class contains useful methods for downloading Images into an application.
A socket is a two-way communication channel between two running programs on a network. The java.net.Socket class can be used to set up communication channels for client/server applications. The server process listens at a socket for requests from a client. The client process requests service from a server listening at a particular socket. Once a connection exists between client and server, input and output streams are used to read and write data over the socket.
