  A new numerical code, designed for the detailed numerical treatment of
nonlinear diffusive shock acceleration, is used for modeling of particle
acceleration and radiation in young supernova remnants. The model is based on
spherically symmetric hydrodynamic equations complemented with transport
equations for relativistic particles. For the first time, the acceleration of
electrons and protons by both forward and reverse shocks is studied through
detailed numerical calculations. We model the energy spectra and spatial
distributions of nonthermal emission of the young supernova remnant RX
J1713.7-3946 and compare the calculations with the spectral and morphological
properties of this object obtained in broad energy band from radio to very high
energy gamma-rays. We discuss the advantages and shortcomings of the so-called
hadronic and leptonic models which assume that the observed TeV gamma-ray
emission is produced by accelerated protons and electrons, respectively. We
discuss also a "composite" scenario when the gamma-ray flux from the main parts
of the shell has inverse Compton origin, but with a non-negligible contribution
of hadronic origin from dense clouds interacting with the shell.
