  The stationary Josephson effect in a system of ballistic graphene is studied
in the framework of quasiclassical Green's function theory. Reflecting the
ultimate two-dimensionality of graphene, a Josephson junction involving a
graphene sheet embodies what we call a planar Josephson junction, in which
superconducting electrodes partially cover the two-dimensional graphene layer,
achieving a planar contact with it. For capturing this feature we employ a
model of tunneling Hamiltonian that also takes account of the effects of
inhomogeneous carrier density. Within the effective mass approximation we
derive a general formula for the Josephson current, revealing characteristic
features of the superconducting proximity effect in the planar Josephson
junction. The same type of analysis has been equally applied to mono-, bi- and
arbitrary $N$-layer cases.
