CaptureListener

The interface that wants to be told when something captures or releases the creature. Capturing is not an eligibility - any creature may be captured, and how a capture works is decided by the item doing it (what it may hold, whether it needs a contract, what it costs - the Spirit Beast Bag's own rule is "your own contracted beast, one at a time"). So only two optional hooks are left:

Member	Description
void onCaptured(@Nullable Player captor)	After the creature is taken, before the entity leaves the world.
void onReleased(@Nullable Player captor)	After the creature is back in a level.

Both do nothing by default: a creature that does not implement this can still be captured, it simply hears nothing; captor is empty when no player did it.

The state of a capture is not part of this interface - a captured beast is recorded in the item's own component, and the interface only has to tell the creature. Eligibility to be contracted is a different interface, see Contractable.