  We analyze the white dwarf population in miniJPAS, the first square degree
observed with 56 medium-band, 145 A in width optical filters by the Javalambre
Physics of the accelerating Universe Astrophysical Survey (J-PAS), to provide a
data-based forecast for the white dwarf science with low-resolution (R ~ 50)
photo-spectra. We define the sample of the bluest point-like sources in
miniJPAS with r < 21.5 mag, point-like probability larger than 0.5, (u-r) <
0.80 mag, and (g-i) < 0.25 mag. This sample comprises 33 sources with
spectroscopic information, 11 white dwarfs and 22 QSOs. We estimate the
effective temperature (Teff), the surface gravity, and the composition of the
white dwarf population by a Bayesian fitting to the observed photo-spectra. The
miniJPAS data permit the classification of the observed white dwarfs into
H-dominated and He-dominated with 99% confidence, and the detection of calcium
absorption and polluting metals down to r ~ 21.5 mag at least for sources with
7000 < Teff < 22000 K, the temperature range covered by the white dwarfs in
miniJPAS. The effective temperature is estimated with a 2% uncertainty, close
to the 1% from spectroscopy. A precise estimation of the surface gravity
depends on the available parallax information. In addition, the white dwarf
population at Teff > 7000 K can be segregated from the bluest extragalactic
QSOs, providing a clean sample based on optical photometry alone. The J-PAS
low-resolution photo-spectra provide precise and accurate effective
temperatures and atmospheric compositions for white dwarfs, complementing the
data from Gaia. J-PAS will also detect and characterize new white dwarfs beyond
the Gaia magnitude limit, providing faint candidates for spectroscopic follow
up.
