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Java in a Nutshell

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The java.net Package
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28.6 java.net.DatagramSocket (JDK 1.0)

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 that they arrived or to resend them if they did not. Thus, packets sent through a DatagramSocket are not guaranteed to arrive in the order sent, or to arrive at all. On the other hand, this low-overhead protocol makes datagram transmission very fast.

If a port is specified when the DatagramSocket is created, that port is used; otherwise, the system assigns a port. getLocalPort() returns the port number in use. 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, into the specified DatagramPacket. close() closes the socket and frees the port it used for reuse. Once close() has been called, the DatagramSocket should not be used again.

See Socket and URL for higher-level interfaces to networking.

public class DatagramSocket extends Object {
    // Public Constructors
            public DatagramSocket() throws SocketException;
            public DatagramSocket(int port) throws SocketException;
        1.1public DatagramSocket(int port, InetAddress laddr) throws SocketException;
    // Public Instance Methods
            public void close();
        1.1public InetAddress getLocalAddress();
            public int getLocalPort();
        1.1public synchronized int getSoTimeout() throws SocketException;
            public synchronized void receive(DatagramPacket p) throws IOException;
            public void send(DatagramPacket p) throws IOException;
        1.1public synchronized void setSoTimeout(int timeout) throws SocketException;
}

Extended By:

MulticastSocket


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