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| Chapter 15 The java.net Package |

# MulticastSocket

## Name

MulticastSocket

## Synopsis

Class Name:

  `java.net.MulticastSocket`

Superclass:

  `java.net.DatagramSocket`

Immediate Subclasses:

  None

Interfaces Implemented:

  None

Availability:

  New as of JDK 1.1

## Description

The `MulticastSocket` class implements packet-oriented, connectionless, multicast data communication. In Internet parlance, this is the User Datagram Protocol (UDP) with additional functionality for joining and leaving groups of other multicast hosts on the Internet. A multicast group is specified by a Class D address, which means that the four highest-order bits are set to 1110. In other words, multicast addresses are in the range 224.0.0.1 through 239.255.255.255 inclusive.

`MulticastSocket` inherits most of its functionality from `DatagramSocket`; it adds the ability to join and leave multicast groups. When a `MulticastSocket` joins a group, it receives all of the packets destined for the group. Any `DatagramSocket` or `MulticastSocket` can send packets to a multicast group.

## Class Summary

    public final class java.net.MulticastSocket
                       extends java.net.DatagramSocket {
      // Constructors
      public MulticastSocket();
      public MulticastSocket(int port);
      // Instance Methods
      public InetAddress getInterface();
      public byte getTTL();
      public void joinGroup(InetAddress mcastaddr);
      public void leaveGroup(InetAddress mcastaddr)
      public synchronized void send(DatagramPacket p, byte ttl);
      public void setInterface(InetAddress inf);
      public void setTTL(byte ttl);
    }

## Constructors

### MulticastSocket

#### public MulticastSocket() throws IOException

Throws

  `IOException`

    If any kind of I/O error occurs.

  `SecurityException`

    If the application is not allowed to listen on the port.

Description

  This constructor creates a `MulticastSocket` that is bound to any available port on the local host machine.

#### public MulticastSocket(int port) throws IOException

Parameters

  `port`

    A port number.

Throws

  `IOException`

    If any kind of I/O error occurs.

  `SecurityException`

    If the application is not allowed to listen on the given port.

Description

  This constructor creates a `MulticastSocket` that is bound to the given port on the local host machine.

## Instance Methods

### getInterface

#### public InetAddress getInterface() throws SocketException

Returns

  The address of the network interface used for outgoing multicast packets.

Throws

  `SocketException`

    If any kind of socket error occurs.

Description

  This method returns the IP address that this `MulticastSocket` uses to send out packets to multicast destinations.

### getTTL

#### public byte getTTL() throws IOException

Returns

  The time-to-live (TTL) value for this socket.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method returns the TTL value for this socket. This value is the number of hops an outgoing packet can traverse before it is discarded.

### joinGroup

#### public void joinGroup(InetAddress mcastaddr) throws IOException

Parameters

  `mcastaddr`

    The IP address of the group to join.

Throws

  `IOException`

    If any kind of I/O error occurs.

  `SecurityException`

    If the application is not allowed to access the given multicast address.

Description

  This method is used to join a multicast group. An exception is thrown if the given address is not a multicast address. While the socket is part of a group, it receives all the packets that are sent to the group.

### leaveGroup

#### public void leaveGroup(InetAddress mcastaddr) throws IOException

Parameters

  `mcastaddr`

    The IP address of the group to leave.

Throws

  `IOException`

    If any kind of I/O error occurs.

  `SecurityException`

    If the application is not allowed to access the given multicast address.

Description

  This method is used to leave a multicast group. An exception is thrown if the given address is not a multicast address.

### send

####

     public synchronized void send(DatagramPacket p, byte ttl) throws IOException

Parameters

  `p`

    The `DatagramPacket` to be sent.

  `ttl`

    The time-to-live (TTL) value for this packet.

Throws

  `IOException`

    If any kind of I/O error occurs.

  `SecurityException`

    If the application is not allowed to send data to the packet's destination.

Description

  This method sends a packet from this socket using the given TTL value. The packet data, packet length, destination address, and destination port number are specified by the given `DatagramPacket`.

  Generally, it is easier to use `setTTL()` to set the TTL value for the socket, then use `send(DatagramPacket)` to send data. This method is provided for special cases.

### setInterface

#### public void setInterface(InetAddress inf) throws SocketException

Parameters

  `inf`

    The new address of the network interface for multicast packets.

Throws

  `SocketException`

    If any kind of socket error occurs.

Description

  This method is used to set the address that is used for outgoing multicast packets.

### setTTL

#### public void setTTL(byte ttl) throws IOException

Parameters

  `ttl`

    The new time-to-live (TTL) value for this socket.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method is used to set the TTL value of the socket. The TTL value is the number of hops an outgoing packet can traverse before it is discarded.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `close()` | `DatagramSocket`
`equals(Object)` | `Object` | `finalize()` | `Object`
`getClass()` | `Object` | `getLocalAddress()` | `DatagramSocket`
`getLocalPort()` | `DatagramSocket` | `getSoTimeout()` | `DatagramSocket`
`hashCode()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `receive(DatagramPacket)` | `DatagramSocket`
`send(DatagramPacket)` | `DatagramSocket` | `setSoTimeout(int)` | `DatagramSocket`
`toString()` | `Object` | `wait()` | `Object`
`wait(long)` | `Object` | `wait(long, int)` | `Object`

## See Also

`DatagramPacket`, `DatagramSocket`, `DatagramSocketImpl`, `InetAddress`, `IOException`, `SecurityException`, `SocketException`

MalformedURLException |  | NoRouteToHostException