This subclass of DatagramSocket can send and receive multicast UDP packets. It extends DatagramSocket by adding joinGroup( ) and leaveGroup( ) methods to join and leave multicast groups. You do not have to join a group to send a packet to a multicast address, but you must join the group to receive packets sent to that address. Note that the use of a MulticastSocket is governed by a security manager.

Use setTimeToLive( ) to set a time-to-live value for any packets sent through a MulticastSocket. This constrains the number of network hops a packet can take and controls the scope of a multicast. Use setInterface( ) or setNetworkInterface( ) to specify the InetAddress or the NetworkInterface that outgoing multicast packets should use: this is useful for servers or other computers that have more than one internet address or network interface. setLoopbackMode( ) specifies whether a multicast packets sent through this socket should be send back to this socket or not. This method should really be named "setLoopbackModeDisabled( )": passing an argument of TRue requests (but does not require) that the system disable loopback packets.

Figure 12-12. java.net.MulticastSocket

public class MulticastSocket extends DatagramSocket {
// Public Constructors
     public MulticastSocket( ) throws java.io.IOException;  
1.4  public MulticastSocket(SocketAddress bindaddr) throws java.io.IOException;  
     public MulticastSocket(int port) throws java.io.IOException;  
// Public Instance Methods
     public InetAddress getInterface( ) 
throws SocketException;     default:Inet4Address
1.4  public boolean getLoopbackMode( ) throws SocketException;    default:false
1.4  public NetworkInterface getNetworkInterface( ) throws SocketException; 
1.2  public int getTimeToLive( ) throws java.io.IOException;     default:1
     public void joinGroup(InetAddress mcastaddr) throws java.io.IOException;
1.4  public void joinGroup(SocketAddress mcastaddr, NetworkInterface netIf) 
throws java.io.IOException;  
     public void leaveGroup(InetAddress mcastaddr) 
throws java.io.IOException;  
1.4  public void leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf) throws java.io.IOException;  
     public void setInterface(InetAddress inf) throws SocketException;  
1.4  public void setLoopbackMode(boolean disable) throws SocketException;  
1.4  public void setNetworkInterface(NetworkInterface netIf) 
throws SocketException;  
1.2  public void setTimeToLive(int ttl) throws java.io.IOException;  
// Deprecated Public Methods
#    public byte getTTL( ) throws java.io.IOException;     default:1
#    public void send(DatagramPacket p, byte ttl) throws java.io.IOException; 
#    public void setTTL(byte ttl) throws java.io.IOException;  
}