Beyond the Basics - TCP/IP Sockets in Java Practical Guide for Programmers - page 83

including 1) allowing specification of the datagram TTL, and 2) allowing the interface through
which datagrams are sent to the group to be specified/changed (an interface is identified by its
Internet address). A multicast receiver, on the other hand, must use a MulticastSocket because
it needs the ability to join a group.
MulticastSocket is a subclass of DatagramSocket , so it provides all of the DatagramSocket
methods. We only present methods specific to or adapted for MulticastSocket .

MulticastSocket

Constructors

MulticastSocket ()
MulticastSocket ( int localPort )
Constructs a datagram socket that can perform some additional multicast operations.
The second form of the constructor specifies the local port. If the local port is not
specified, the socket is bound to any available local port.
localPort Local port. A localPort of 0 allows the constructor to pick

any available port.

Operators

void joinGroup ( InetAddress groupAddress )
void leaveGroup ( InetAddress groupAddress )
Join/leave a multicast group. A socket may be a member of multiple groups simulta-
neously. Joining a group of which this socket is already a member or leaving a group
of which this socket is not a member may generate an exception.
groupAddress Multicast address identifying group

void send ( DatagramPacket packet , byte TTL )
Send a datagram from this socket with the specified TTL.
packet Packet to transmit. Either the packet must specify a

destination address or the UDP socket must have a specified
remote address and port (see connect() ).

TTL Time to live for this packet

Accessors

InetAddress getInterface ()
void setInterface ( InetAddress interface )
Returns/sets the interface to use for multicast operations on this socket. This is
primarily used on hosts with multiple interfaces. Join/leave requests and datagrams