L−C oscillation is not realistic for two reasons.
(i) Every inductor has some resistance. The effect of this resistance is to introduce a damping effect on the charge and current in the circuit and the oscillations finally die away.
(ii) Even, if the resistance in L−C circuit were zero, the total energy of the system would not remain constant. It is radiated away from the system in the form of electromagnetic waves. In fact during the process of charging and discharging of capacitor, electrons travel between plates with acceleration. Their accelerated movement causes radiation of energy by EM waves.