  With a view toward application of the Pauli-Villars regularization method to
the Casimir energy of boundaries, we calculate the expectation values of the
components of the stress tensor of a confined massive field in 1+1 space-time
dimensions. Previous papers by Hays and Fulling are bridged and generalized.
The Green function for the time-independent Schrodinger equation is constructed
from the Green function for the whole line by the method of images;
equivalently, the one-dimensional system is solved exactly in terms of closed
classical paths and periodic orbits. Terms in the energy density and in the
eigenvalue density attributable to the two boundaries individually and those
attributable to the confinement of the field to a finite interval are
distinguished so that their physical origins are clear. Then the pressure is
found similarly from the cylinder kernel, the Green function associated most
directly with an exponential frequency cutoff of the Fourier mode expansion.
Finally, we discuss how the theory could be rendered finite by the
Pauli-Villars method.
