In an ideal parallel LC circuit, the capacitor is charged by connecting it to a DC source which is then disconnected. The current in the circuit

When capacitor is connected to a DC source and then disconnected, it gets charged and then it starts discharging through the inductor. When capacitor C is fully charged to q₀,the current in inductor L is zero. At this instant an amount of energy $\frac{1}{2}\frac{{\mathrm{q}}_0^2}{\mathrm{C}}$ is stored in electric field between the plates of the capacitor.

When circuit is closed, the capacitor begins to discharge through the inductor causing current to flow. The energy of electric field between the
capacitor plates has transferred to magnetic field. By Lenz's law the dying magnetic field induces an emf in the inductance in the same direction as current.

Hence, L-C circuit sets up oscillations.