J2ME in a Nutshell

Name

Datagram

Synopsis

A Datagram represents a message to be sent from a sender to a receiver. A Datagram consists of an arbitrary sequence of bytes together with an address. Datagram objects are created using the newDatagram() method of the DatagramConnection class.

When preparing a Datagram for transmission, the data content must be set using the setData() method, which requires the data to be supplied in the form of an array of bytes, where the offset and len arguments specify the portion of the array that is to be used to form the message body. The maximum permitted length of a Datagram can be obtained from the DatagramConnection object. The data length associated with the Datagram can be changed using the setLength() method, but it cannot be increased beyond the end of the buffer supplied by the setData method. The reset() method is used to set the offset and length values to zero. This method is often used when creating the message body using the DataOutput interface methods.

A Datagram must have a destination address, which is set using one of the two setAddress() methods. One variant allows the address to be copied from another Datagram, which is a convenient when creating a response to a received Datagram. The other variant accepts a string of the form datagram://host:port, where host is the host name or IP address of the destination and port is the destination’s port number. A Datagram without a destination address to be sent using a DatagramConnection in client mode ...