<:> Summary

The basic approach for MIDI output is

create a Sequence with some Track objects.
Add MidiEvents containing suitably constructed ShortMessages (e.g., NOTE_ON and NOTE_OFF messages) to one of the tracks.
Set the sequence on the Sequencer and call start.

The relevant notes etc. get sent at the specified times.

For sound synthesis, consider using one of the public-domain packages such as JSyn from http://www.softsynth.com/jsyn.