public DatagramSocket() throws SocketException 
{
        // create a datagram socket.
        createImpl();
        try {
            bind(new InetSocketAddress(0));
        } catch (SocketException se) {
            throw se;
        } catch(IOException e) {
            throw new SocketException(e.getMessage());
        }
}

Constructs a datagram socket and binds it to any available port on the local host machine. The socket will be bound to the wildcard address, an IP address chosen by the kernel.

If there is a security manager, its checkListen method is first called with 0 as its argument to ensure the operation is allowed. This could result in a SecurityException.

Throws:

SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

Also see:

SecurityManager#checkListen
exception: SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

exception: SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

 protected DatagramSocket(DatagramSocketImpl impl) 
{
        if (impl == null)
            throw new NullPointerException();
        this.impl = impl;
        checkOldImpl();
}

Creates an unbound datagram socket with the specified DatagramSocketImpl.

Parameters:

impl - an instance of a DatagramSocketImpl the subclass wishes to use on the DatagramSocket.

since: 1.4 -

 public DatagramSocket(SocketAddress bindaddr) throws SocketException 
{
        // create a datagram socket.
        createImpl();
        if (bindaddr != null) {
            bind(bindaddr);
        }
}

Creates a datagram socket, bound to the specified local socket address.

If, if the address is null, creates an unbound socket.

If there is a security manager, its checkListen method is first called with the port from the socket address as its argument to ensure the operation is allowed. This could result in a SecurityException.

Parameters:

bindaddr - local socket address to bind, or null for an unbound socket.

Throws:

SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

Also see:

SecurityManager#checkListen
exception: SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

exception: SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

since: 1.4 -

 public DatagramSocket(int port) throws SocketException 
{
        this(port, null);
}

Constructs a datagram socket and binds it to the specified port on the local host machine. The socket will be bound to the wildcard address, an IP address chosen by the kernel.

If there is a security manager, its checkListen method is first called with the port argument as its argument to ensure the operation is allowed. This could result in a SecurityException.

Parameters:

port - port to use.

Throws:

SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

Also see:

SecurityManager#checkListen
exception: SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

exception: SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

 public DatagramSocket(int port,
    InetAddress laddr) throws SocketException 
{
        this(new InetSocketAddress(laddr, port));
}

Creates a datagram socket, bound to the specified local address. The local port must be between 0 and 65535 inclusive. If the IP address is 0.0.0.0, the socket will be bound to the wildcard address, an IP address chosen by the kernel.

If there is a security manager, its checkListen method is first called with the port argument as its argument to ensure the operation is allowed. This could result in a SecurityException.

Parameters:

port - local port to use

laddr - local address to bind

Throws:

SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

Also see:

SecurityManager#checkListen
exception: SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

exception: SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

since: JDK1.1 -

 public synchronized  void bind(SocketAddress addr) throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (isBound())
            throw new SocketException("already bound");
        if (addr == null)
            addr = new InetSocketAddress(0);
        if (!(addr instanceof InetSocketAddress))
            throw new IllegalArgumentException("Unsupported address type!");
        InetSocketAddress epoint = (InetSocketAddress) addr;
        if (epoint.isUnresolved())
            throw new SocketException("Unresolved address");
        SecurityManager sec = System.getSecurityManager();
        if (sec != null) {
            sec.checkListen(epoint.getPort());
        }
        try {
            getImpl().bind(epoint.getPort(),
                           epoint.getAddress());
        } catch (SocketException e) {
            getImpl().close();
            throw e;
        }
        bound = true;
}

Binds this DatagramSocket to a specific address & port.

If the address is null, then the system will pick up an ephemeral port and a valid local address to bind the socket.

 public  void close() 
{
        synchronized(closeLock) {
            if (isClosed())
                return;
            impl.close();
            closed = true;
        }
}

Closes this datagram socket.

Any thread currently blocked in #receive upon this socket will throw a SocketException .

If this socket has an associated channel then the channel is closed as well.

 public  void connect(SocketAddress addr) throws SocketException 
{
        if (addr == null)
            throw new IllegalArgumentException("Address can't be null");
        if (!(addr instanceof InetSocketAddress))
            throw new IllegalArgumentException("Unsupported address type");
        InetSocketAddress epoint = (InetSocketAddress) addr;
        if (epoint.isUnresolved())
            throw new SocketException("Unresolved address");
        connectInternal(epoint.getAddress(), epoint.getPort());
}

Connects this socket to a remote socket address (IP address + port number).

 public  void connect(InetAddress address,
    int port) 
{
        try {
            connectInternal(address, port);
        } catch (SocketException se) {
            throw new Error("connect failed", se);
        }
}

Connects the socket to a remote address for this socket. When a socket is connected to a remote address, packets may only be sent to or received from that address. By default a datagram socket is not connected.

If the remote destination to which the socket is connected does not exist, or is otherwise unreachable, and if an ICMP destination unreachable packet has been received for that address, then a subsequent call to send or receive may throw a PortUnreachableException. Note, there is no guarantee that the exception will be thrown.

A caller's permission to send and receive datagrams to a given host and port are checked at connect time. When a socket is connected, receive and send will not perform any security checks on incoming and outgoing packets, other than matching the packet's and the socket's address and port. On a send operation, if the packet's address is set and the packet's address and the socket's address do not match, an IllegalArgumentException will be thrown. A socket connected to a multicast address may only be used to send packets.

  void createImpl() throws SocketException 
{
        
        if (impl == null) {
            if (factory != null) {
                impl = factory.createDatagramSocketImpl();
                checkOldImpl();
            } else {
                boolean isMulticast = (this instanceof MulticastSocket) ? true : false;
                impl = DefaultDatagramSocketImplFactory.createDatagramSocketImpl(isMulticast);
                checkOldImpl();
            }
        }
        // creates a udp socket
        impl.create();
        created = true;
}

 public  void disconnect() 
{
        synchronized (this) {
            if (isClosed())
                return;
            if (connectState == ST_CONNECTED) {
                impl.disconnect ();
            }
            connectedAddress = null;
            connectedPort = -1;
            connectState = ST_NOT_CONNECTED;
        }
}

Disconnects the socket. If the socket is closed or not connected, then this method has no effect.

 public synchronized boolean getBroadcast() throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        return ((Boolean)(getImpl().getOption(SocketOptions.SO_BROADCAST))).booleanValue();
}

Tests if SO_BROADCAST is enabled.

 public DatagramChannel getChannel() 
{
        return null;
}

Returns the unique java.nio.channels.DatagramChannel object associated with this datagram socket, if any.

A datagram socket will have a channel if, and only if, the channel itself was created via the DatagramChannel.open method.

 DatagramSocketImpl getImpl() throws SocketException 
{
        if (!created)
            createImpl();
        return impl;
}

Get the DatagramSocketImpl attached to this socket, creating it if necessary.

 public InetAddress getInetAddress() 
{
        return connectedAddress;
}

Returns the address to which this socket is connected. Returns null if the socket is not connected.

If the socket was connected prior to being closed , then this method will continue to return the connected address after the socket is closed.

 public InetAddress getLocalAddress() 
{
        if (isClosed())
            return null;
        InetAddress in = null;
        try {
            in = (InetAddress) getImpl().getOption(SocketOptions.SO_BINDADDR);
            if (in.isAnyLocalAddress()) {
                in = InetAddress.anyLocalAddress();
            }
            SecurityManager s = System.getSecurityManager();
            if (s != null) {
                s.checkConnect(in.getHostAddress(), -1);
            }
        } catch (Exception e) {
            in = InetAddress.anyLocalAddress(); // "0.0.0.0"
        }
        return in;
}

Gets the local address to which the socket is bound.

If there is a security manager, its checkConnect method is first called with the host address and -1 as its arguments to see if the operation is allowed.

 public int getLocalPort() 
{
        if (isClosed())
            return -1;
        try {
            return getImpl().getLocalPort();
        } catch (Exception e) {
            return 0;
        }
}

Returns the port number on the local host to which this socket is bound.

 public SocketAddress getLocalSocketAddress() 
{
        if (isClosed())
            return null;
        if (!isBound())
            return null;
        return new InetSocketAddress(getLocalAddress(), getLocalPort());
}

Returns the address of the endpoint this socket is bound to.

 public int getPort() 
{
        return connectedPort;
}

Returns the port number to which this socket is connected. Returns -1 if the socket is not connected.

If the socket was connected prior to being closed , then this method will continue to return the connected port number after the socket is closed.

 public synchronized int getReceiveBufferSize() throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        int result = 0;
        Object o = getImpl().getOption(SocketOptions.SO_RCVBUF);
        if (o instanceof Integer) {
            result = ((Integer)o).intValue();
        }
        return result;
}

Get value of the SO_RCVBUF option for this DatagramSocket, that is the buffer size used by the platform for input on this DatagramSocket.

 public SocketAddress getRemoteSocketAddress() 
{
        if (!isConnected())
            return null;
        return new InetSocketAddress(getInetAddress(), getPort());
}

Returns the address of the endpoint this socket is connected to, or null if it is unconnected.

If the socket was connected prior to being closed , then this method will continue to return the connected address after the socket is closed.

 public synchronized boolean getReuseAddress() throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        Object o = getImpl().getOption(SocketOptions.SO_REUSEADDR);
        return ((Boolean)o).booleanValue();
}

Tests if SO_REUSEADDR is enabled.

 public synchronized int getSendBufferSize() throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        int result = 0;
        Object o = getImpl().getOption(SocketOptions.SO_SNDBUF);
        if (o instanceof Integer) {
            result = ((Integer)o).intValue();
        }
        return result;
}

Get value of the SO_SNDBUF option for this DatagramSocket, that is the buffer size used by the platform for output on this DatagramSocket.

 public synchronized int getSoTimeout() throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (getImpl() == null)
            return 0;
        Object o = getImpl().getOption(SocketOptions.SO_TIMEOUT);
        /* extra type safety */
        if (o instanceof Integer) {
            return ((Integer) o).intValue();
        } else {
            return 0;
        }
}

Retrieve setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).

 public synchronized int getTrafficClass() throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        return ((Integer)(getImpl().getOption(SocketOptions.IP_TOS))).intValue();
}

Gets traffic class or type-of-service in the IP datagram header for packets sent from this DatagramSocket.

As the underlying network implementation may ignore the traffic class or type-of-service set using #setTrafficClass(int) this method may return a different value than was previously set using the #setTrafficClass(int) method on this DatagramSocket.

 public boolean isBound() 
{
        return bound;
}

Returns the binding state of the socket.

If the socket was bound prior to being closed , then this method will continue to return true after the socket is closed.

 public boolean isClosed() 
{
        synchronized(closeLock) {
            return closed;
        }
}

Returns whether the socket is closed or not.

 public boolean isConnected() 
{
        return connectState != ST_NOT_CONNECTED;
}

Returns the connection state of the socket.

If the socket was connected prior to being closed , then this method will continue to return true after the socket is closed.

 public synchronized  void receive(DatagramPacket p) throws IOException 
{
        synchronized (p) {
            if (!isBound())
                bind(new InetSocketAddress(0));
            if (connectState == ST_NOT_CONNECTED) {
                // check the address is ok with the security manager before every recv.
                SecurityManager security = System.getSecurityManager();
                if (security != null) {
                    while(true) {
                        String peekAd = null;
                        int peekPort = 0;
                        // peek at the packet to see who it is from.
                        if (!oldImpl) {
                            // We can use the new peekData() API
                            DatagramPacket peekPacket = new DatagramPacket(new byte[1], 1);
                            peekPort = getImpl().peekData(peekPacket);
                            peekAd = peekPacket.getAddress().getHostAddress();
                        } else {
                            InetAddress adr = new InetAddress();
                            peekPort = getImpl().peek(adr);
                            peekAd = adr.getHostAddress();
                        }
                        try {
                            security.checkAccept(peekAd, peekPort);
                            // security check succeeded - so now break
                            // and recv the packet.
                            break;
                        } catch (SecurityException se) {
                            // Throw away the offending packet by consuming
                            // it in a tmp buffer.
                            DatagramPacket tmp = new DatagramPacket(new byte[1], 1);
                            getImpl().receive(tmp);
                            // silently discard the offending packet
                            // and continue: unknown/malicious
                            // entities on nets should not make
                            // runtime throw security exception and
                            // disrupt the applet by sending random
                            // datagram packets.
                            continue;
                        }
                    } // end of while
                }
            }
            if (connectState == ST_CONNECTED_NO_IMPL) {
                // We have to do the filtering the old fashioned way since
                // the native impl doesn't support connect or the connect
                // via the impl failed.
                boolean stop = false;
                while (!stop) {
                    // peek at the packet to see who it is from.
                    InetAddress peekAddress = new InetAddress();
                    int peekPort = getImpl().peek(peekAddress);
                    if ((!connectedAddress.equals(peekAddress)) ||
                        (connectedPort != peekPort)) {
                        // throw the packet away and silently continue
                        DatagramPacket tmp = new DatagramPacket(new byte[1], 1);
                        getImpl().receive(tmp);
                    } else {
                        stop = true;
                    }
                }
            }
            // If the security check succeeds, or the datagram is
            // connected then receive the packet
            getImpl().receive(p);
        }
}

Receives a datagram packet from this socket. When this method returns, the DatagramPacket's buffer is filled with the data received. The datagram packet also contains the sender's IP address, and the port number on the sender's machine.

This method blocks until a datagram is received. The length field of the datagram packet object contains the length of the received message. If the message is longer than the packet's length, the message is truncated.

If there is a security manager, a packet cannot be received if the security manager's checkAccept method does not allow it.

 public  void send(DatagramPacket p) throws IOException 
{
        InetAddress packetAddress = null;
        synchronized (p) {
            if (isClosed())
                throw new SocketException("Socket is closed");
            if (connectState == ST_NOT_CONNECTED) {
                // check the address is ok wiht the security manager on every send.
                SecurityManager security = System.getSecurityManager();
                // The reason you want to synchronize on datagram packet
                // is because you dont want an applet to change the address
                // while you are trying to send the packet for example
                // after the security check but before the send.
                if (security != null) {
                    if (p.getAddress().isMulticastAddress()) {
                        security.checkMulticast(p.getAddress());
                    } else {
                        security.checkConnect(p.getAddress().getHostAddress(),
                                              p.getPort());
                    }
                }
            } else {
                // we're connected
                packetAddress = p.getAddress();
                if (packetAddress == null) {
                    p.setAddress(connectedAddress);
                    p.setPort(connectedPort);
                } else if ((!packetAddress.equals(connectedAddress)) ||
                           p.getPort() != connectedPort) {
                    throw new IllegalArgumentException("connected address " +
                                                       "and packet address" +
                                                       " differ");
                }
            }
            // Check whether the socket is bound
            if (!isBound())
                bind(new InetSocketAddress(0));
            // call the  method to send
            getImpl().send(p);
        }
}

Sends a datagram packet from this socket. The DatagramPacket includes information indicating the data to be sent, its length, the IP address of the remote host, and the port number on the remote host.

If there is a security manager, and the socket is not currently connected to a remote address, this method first performs some security checks. First, if p.getAddress().isMulticastAddress() is true, this method calls the security manager's checkMulticast method with p.getAddress() as its argument. If the evaluation of that expression is false, this method instead calls the security manager's checkConnect method with arguments p.getAddress().getHostAddress() and p.getPort(). Each call to a security manager method could result in a SecurityException if the operation is not allowed.

 public synchronized  void setBroadcast(boolean on) throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_BROADCAST, Boolean.valueOf(on));
}

Enable/disable SO_BROADCAST.

 public static synchronized  void setDatagramSocketImplFactory(DatagramSocketImplFactory fac) throws IOException 
{
        if (factory != null) {
            throw new SocketException("factory already defined");
        }
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkSetFactory();
        }
        factory = fac;
}

Sets the datagram socket implementation factory for the application. The factory can be specified only once.

When an application creates a new datagram socket, the socket implementation factory's createDatagramSocketImpl method is called to create the actual datagram socket implementation.

Passing null to the method is a no-op unless the factory was already set.

If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException.

 public synchronized  void setReceiveBufferSize(int size) throws SocketException 
{
        if (size < = 0) {
            throw new IllegalArgumentException("invalid receive size");
        }
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_RCVBUF, new Integer(size));
}

Sets the SO_RCVBUF option to the specified value for this DatagramSocket. The SO_RCVBUF option is used by the the network implementation as a hint to size the underlying network I/O buffers. The SO_RCVBUF setting may also be used by the network implementation to determine the maximum size of the packet that can be received on this socket.

Because SO_RCVBUF is a hint, applications that want to verify what size the buffers were set to should call #getReceiveBufferSize() .

Increasing SO_RCVBUF may allow the network implementation to buffer multiple packets when packets arrive faster than are being received using #receive(DatagramPacket) .

Note: It is implementation specific if a packet larger than SO_RCVBUF can be received.

 public synchronized  void setReuseAddress(boolean on) throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        // Integer instead of Boolean for compatibility with older DatagramSocketImpl
        if (oldImpl)
            getImpl().setOption(SocketOptions.SO_REUSEADDR, new Integer(on?-1:0));
        else
            getImpl().setOption(SocketOptions.SO_REUSEADDR, Boolean.valueOf(on));
}

Enable/disable the SO_REUSEADDR socket option.

For UDP sockets it may be necessary to bind more than one socket to the same socket address. This is typically for the purpose of receiving multicast packets (See java.net.MulticastSocket ). The SO_REUSEADDR socket option allows multiple sockets to be bound to the same socket address if the SO_REUSEADDR socket option is enabled prior to binding the socket using #bind(SocketAddress) .

Note: This functionality is not supported by all existing platforms, so it is implementation specific whether this option will be ignored or not. However, if it is not supported then #getReuseAddress() will always return false.

When a DatagramSocket is created the initial setting of SO_REUSEADDR is disabled.

The behaviour when SO_REUSEADDR is enabled or disabled after a socket is bound (See #isBound() ) is not defined.

 public synchronized  void setSendBufferSize(int size) throws SocketException 
{
        if (!(size  > 0)) {
            throw new IllegalArgumentException("negative send size");
        }
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_SNDBUF, new Integer(size));
}

Sets the SO_SNDBUF option to the specified value for this DatagramSocket. The SO_SNDBUF option is used by the network implementation as a hint to size the underlying network I/O buffers. The SO_SNDBUF setting may also be used by the network implementation to determine the maximum size of the packet that can be sent on this socket.

As SO_SNDBUF is a hint, applications that want to verify what size the buffer is should call #getSendBufferSize() .

Increasing the buffer size may allow multiple outgoing packets to be queued by the network implementation when the send rate is high.

Note: If #send(DatagramPacket) is used to send a DatagramPacket that is larger than the setting of SO_SNDBUF then it is implementation specific if the packet is sent or discarded.

 public synchronized  void setSoTimeout(int timeout) throws SocketException 
{
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_TIMEOUT, new Integer(timeout));
}

Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a call to receive() for this DatagramSocket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the DatagramSocket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout.

 public synchronized  void setTrafficClass(int tc) throws SocketException 
{
        if (tc <  0 || tc  > 255)
            throw new IllegalArgumentException("tc is not in range 0 -- 255");
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.IP_TOS, new Integer(tc));
}

Sets traffic class or type-of-service octet in the IP datagram header for datagrams sent from this DatagramSocket. As the underlying network implementation may ignore this value applications should consider it a hint.

The tc must be in the range 0 <= tc <= 255 or an IllegalArgumentException will be thrown.

Notes:

For Internet Protocol v4 the value consists of an integer, the least significant 8 bits of which represent the value of the TOS octet in IP packets sent by the socket. RFC 1349 defines the TOS values as follows:

• IPTOS_LOWCOST (0x02)
• IPTOS_RELIABILITY (0x04)
• IPTOS_THROUGHPUT (0x08)
• IPTOS_LOWDELAY (0x10)
The last low order bit is always ignored as this corresponds to the MBZ (must be zero) bit.

Setting bits in the precedence field may result in a SocketException indicating that the operation is not permitted.

for Internet Protocol v6 tc is the value that would be placed into the sin6_flowinfo field of the IP header.