Java in a Nutshell, 5th Edition

Name

DatagramSocket

Synopsis

This class defines a socket that can receive and send unreliable datagram packets over the network using the UDP protocol. A datagram is a very low-level networking interface: it is simply an array of bytes sent over the network. A datagram does not implement any kind of stream-based communication protocol, and there is no connection established between the sender and the receiver. Datagram packets are called unreliable because the protocol does not make any attempt to ensure they arrive or to resend them if they don’t. Thus, packets sent through a DatagramSocket are not guaranteed to arrive in the order sent or even to arrive at all. On the other hand, this low-overhead protocol makes datagram transmission very fast. See Socket and URL for higher-level interfaces to networking. This class was introduced in Java 1.0, and was enhanced in Java 1.4 to allow local and remote addresses to be specified using the protocol-independent SocketAddress class.

send( ) sends a DatagramPacket through the socket. The packet must contain the destination address to which it should be sent. receive( ) waits for data to arrive at the socket and stores it, along with the address of the sender, in the specified DatagramPacket. close( ) closes the socket and frees the local port for reuse. Once close( ) has been called, the DatagramSocket should not be used again, except to call the isClosed( ) method which returns true if the socket has been closed.

Each time a packet ...