Before data is sent across the Internet from one host to another, it is split into packets of varying but finite size called datagrams. Datagrams range in size from a few dozen bytes to about 60,000 bytes. Anything larger, and often things smaller, must be split into smaller pieces before it can be transmitted. The advantage of this scheme is that if one packet is lost, it can be retransmitted without requiring redelivery of all other packets. Furthermore, if packets arrive out of order, they can be reordered at the receiving end of the connection.

Fortunately, packets are invisible to the Java programmer. The host’s native networking software splits data into packets on the sending end and reassembles packets on the receiving end. Instead, the Java programmer is presented with a higher-level abstraction called a socket. The socket represents a reliable connection for the transmission of data between two hosts. It isolates you from the details of packet encodings, lost and retransmitted packets, and packets that arrive out of order. A socket performs four fundamental operations:

  1. Connect to a remote machine

  2. Send data

  3. Receive data

  4. Close the connection

A socket may not be connected to more than one host at a time. However, a socket may both send data to and receive data from the host to which it’s connected.

The class is Java’s interface to a network socket and allows you to perform all four fundamental socket operations. It provides raw, uninterpreted communication ...

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