Yeap, they always have both inductors and capacitors to exchange energy efficiently with an ideal loss of 0. Obviously, since in real life both inductors and caps have parasitic resistances, the circuit can't never provide an efficiency of 100%.
Now if your concern is... "why not JUST using caps and avoid the inductors" you can see (after deriving the expressions) that when you transfer energy between capacitors there is also an intrinsic energy loss due to spiking... now if you have caps and inductors they both serve as temporary voltage/current sources for one-another making the energy transfer smooth and loss-less.
Hope this helps,
diemilio