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Documentation on the freehep-stdhep classes is available here:
http://java.freehep.org/freehep-stdhep/apidocs/index.html
Documentation on the freehep-physics classes (only necessary if you want the more OO access to stdhep events) is here:
http://java.freehep.org/freehep-physics/apidocs/index.html
Note in particular the StdhepConverter class.