  Superradiance is known as a wave amplification process caused by rotating or
charged black holes. We argue that the superradiance of stationary black holes
in asymptotically AdS spacetimes can be characterized by the ability of energy
extraction. Specifically, we demonstrate that energy can be extracted from
Reissner-Nordstr\"{o}m-AdS$_4$ and Kerr-AdS$_4$ under appropriate
time-dependent boundary conditions at conformal boundaries. This indicates that
energy can be extracted from thermal states dual to these black holes by
applying appropriate time-dependent sources. We also show that the energy
extraction can be realized as a reversible process.
