Is there a Java ClearCase API?
Update 2016 (as mentioned by hack's answer below)
I mentioned since 2010 the CM API multiple times, as soon as 2012 and as recently as last March 2016.
Since ClearTeam 8.x, this API does support dynamic view, as well as snapshot views with 8.0.1.7.
See more with Rational ClearCase CM API introduction (v 9.0.0).
Its "installation and setup requirements" do involve Java, with at least:
Original answer (2010, pre ClearCase Team Explorer)
The is no Java API dedicated for ClearCase.
There is a Java CM API, but about the Rational CM Server used by CCRC (a light-client installation, a simple web server which will forward all request to the actual ClearCase VOB server), not for ClearCase per se: