DatagramPacket

AI-generated Key Takeaways

• DatagramPacket encapsulates data for connectionless, unreliable communication between applications.

• It provides constructors for both sending and receiving datagrams, specifying data, addresses, and ports.

• Key methods allow access and manipulation of the packet's data, address, and port information.

• Used with DatagramSocket for sending and receiving datagrams over a network.

• Inherently unreliable; packets may arrive out of order or be lost during transmission.

public final class DatagramPacket extends Object

This class represents a datagram packet.

Datagram packets are used to implement a connectionless packet delivery service. Each message is routed from one machine to another based solely on information contained within that packet. Multiple packets sent from one machine to another might be routed differently, and might arrive in any order. Packet delivery is not guaranteed.

Public Constructor Summary

	DatagramPacket(byte[] buf, int offset, int length) Constructs a DatagramPacket for receiving packets of length length, specifying an offset into the buffer.
	DatagramPacket(byte[] buf, int length) Constructs a DatagramPacket for receiving packets of length length.
	DatagramPacket(byte[] buf, int offset, int length, InetAddress address, int port) Constructs a datagram packet for sending packets of length length with offset ioffsetto the specified port number on the specified host.
	DatagramPacket(byte[] buf, int offset, int length, SocketAddress address) Constructs a datagram packet for sending packets of length length with offset ioffsetto the specified port number on the specified host.
	DatagramPacket(byte[] buf, int length, InetAddress address, int port) Constructs a datagram packet for sending packets of length length to the specified port number on the specified host.
	DatagramPacket(byte[] buf, int length, SocketAddress address) Constructs a datagram packet for sending packets of length length to the specified port number on the specified host.

Public Method Summary

synchronized InetAddress	getAddress() Returns the IP address of the machine to which this datagram is being sent or from which the datagram was received.
synchronized byte[]	getData() Returns the data buffer.
synchronized int	getLength() Returns the length of the data to be sent or the length of the data received.
synchronized int	getOffset() Returns the offset of the data to be sent or the offset of the data received.
synchronized int	getPort() Returns the port number on the remote host to which this datagram is being sent or from which the datagram was received.
synchronized SocketAddress	getSocketAddress() Gets the SocketAddress (usually IP address + port number) of the remote host that this packet is being sent to or is coming from.
synchronized void	setAddress(InetAddress iaddr) Sets the IP address of the machine to which this datagram is being sent.
synchronized void	setData(byte[] buf, int offset, int length) Set the data buffer for this packet.
synchronized void	setData(byte[] buf) Set the data buffer for this packet.
synchronized void	setLength(int length) Set the length for this packet.
synchronized void	setPort(int iport) Sets the port number on the remote host to which this datagram is being sent.
synchronized void	setSocketAddress(SocketAddress address) Sets the SocketAddress (usually IP address + port number) of the remote host to which this datagram is being sent.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public DatagramPacket (byte[] buf, int offset, int length)

Constructs a DatagramPacket for receiving packets of length length, specifying an offset into the buffer.

The length argument must be less than or equal to buf.length.

Parameters

buf	buffer for holding the incoming datagram.
offset	the offset for the buffer
length	the number of bytes to read.

public DatagramPacket (byte[] buf, int length)

Constructs a DatagramPacket for receiving packets of length length.

The length argument must be less than or equal to buf.length.

Parameters

buf	buffer for holding the incoming datagram.
length	the number of bytes to read.

public DatagramPacket (byte[] buf, int offset, int length, InetAddress address, int port)

Constructs a datagram packet for sending packets of length length with offset ioffsetto the specified port number on the specified host. The length argument must be less than or equal to buf.length.

Parameters

buf	the packet data.
offset	the packet data offset.
length	the packet data length.
address	the destination address.
port	the destination port number.

See Also

• InetAddress

public DatagramPacket (byte[] buf, int offset, int length, SocketAddress address)

Constructs a datagram packet for sending packets of length length with offset ioffsetto the specified port number on the specified host. The length argument must be less than or equal to buf.length.

Android note: Up to and including API 25 this method declared that a SocketException can be thrown, although the exception is never thrown. Code compiled against a newer SDK does not need to catch the exception and will be binary compatible with older versions of Android.

Parameters

buf	the packet data.
offset	the packet data offset.
length	the packet data length.
address	the destination socket address.

Throws

IllegalArgumentException	if address type is not supported

See Also

• InetAddress

public DatagramPacket (byte[] buf, int length, InetAddress address, int port)

Constructs a datagram packet for sending packets of length length to the specified port number on the specified host. The length argument must be less than or equal to buf.length.

Android note: Up to and including API 25 this method declared that a SocketException can be thrown, although the exception is never thrown. Code compiled against a newer SDK does not need to catch the exception and will be binary compatible with older versions of Android.

Parameters

buf	the packet data.
length	the packet length.
address	the destination address.
port	the destination port number.

See Also

• InetAddress

public DatagramPacket (byte[] buf, int length, SocketAddress address)

Constructs a datagram packet for sending packets of length length to the specified port number on the specified host. The length argument must be less than or equal to buf.length.

Parameters

buf	the packet data.
length	the packet length.
address	the destination address.

Throws

IllegalArgumentException	if address type is not supported

See Also

• InetAddress

Public Methods

public synchronized InetAddress getAddress ()

Returns the IP address of the machine to which this datagram is being sent or from which the datagram was received.

Returns

• the IP address of the machine to which this datagram is being sent or from which the datagram was received.

See Also

• InetAddress
• setAddress(java.net.InetAddress)

public synchronized byte[] getData ()

Returns the data buffer. The data received or the data to be sent starts from the offset in the buffer, and runs for length long.

Returns

• the buffer used to receive or send data

See Also

• setData(byte[], int, int)

public synchronized int getLength ()

Returns the length of the data to be sent or the length of the data received.

Returns

• the length of the data to be sent or the length of the data received.

See Also

• setLength(int)

public synchronized int getOffset ()

Returns the offset of the data to be sent or the offset of the data received.

Returns

• the offset of the data to be sent or the offset of the data received.

public synchronized int getPort ()

Returns the port number on the remote host to which this datagram is being sent or from which the datagram was received.

Returns

• the port number on the remote host to which this datagram is being sent or from which the datagram was received.

See Also

• setPort(int)

public synchronized SocketAddress getSocketAddress ()

Gets the SocketAddress (usually IP address + port number) of the remote host that this packet is being sent to or is coming from.

Returns

• the SocketAddress

See Also

• setSocketAddress(SocketAddress)

public synchronized void setAddress (InetAddress iaddr)

Sets the IP address of the machine to which this datagram is being sent.

Parameters

iaddr	the InetAddress

See Also

• getAddress()

public synchronized void setData (byte[] buf, int offset, int length)

Set the data buffer for this packet. This sets the data, length and offset of the packet.

Parameters

buf	the buffer to set for this packet
offset	the offset into the data
length	the length of the data and/or the length of the buffer used to receive data

Throws

NullPointerException	if the argument is null

See Also

• getData()
• getOffset()
• getLength()

public synchronized void setData (byte[] buf)

Set the data buffer for this packet. With the offset of this DatagramPacket set to 0, and the length set to the length of buf.

Parameters

buf	the buffer to set for this packet.

Throws

NullPointerException	if the argument is null.

See Also

• getLength()
• getData()

public synchronized void setLength (int length)

Set the length for this packet. The length of the packet is the number of bytes from the packet's data buffer that will be sent, or the number of bytes of the packet's data buffer that will be used for receiving data. The length must be lesser or equal to the offset plus the length of the packet's buffer.

Parameters

length	the length to set for this packet.

Throws

IllegalArgumentException	if the length is negative of if the length is greater than the packet's data buffer length.

See Also

• getLength()
• setData(byte[])

public synchronized void setPort (int iport)

Sets the port number on the remote host to which this datagram is being sent.

Parameters

iport	the port number

See Also

• getPort()

public synchronized void setSocketAddress (SocketAddress address)

Sets the SocketAddress (usually IP address + port number) of the remote host to which this datagram is being sent.

Parameters

address	the SocketAddress

Throws

IllegalArgumentException	if address is null or is a SocketAddress subclass not supported by this socket

See Also

• getSocketAddress()