  We calculate the phase, the temperature and the junction length dependence of
the supercurrent for ballistic graphene Josephson-junctions. For low
temperatures we find non-sinusoidal dependence of the supercurrent on the
superconductor phase difference for both short and long junctions. The
skewness, which characterizes the deviation of the current-phase relation from
a simple sinusoidal one, shows a linear dependence on the critical current for
small currents. We discuss the similarities and differences with respect to the
classical theory of Josephson junctions, where the weak link is formed by a
diffusive or ballistic metal. The relation to other recent theoretical results
on graphene Josephson junctions is pointed out and the possible experimental
relevance of our work is considered as well.
