Uses of Interface

Packages that use PersistentDataHolder
The root package of the Bukkit API, contains generalized API classes.
Classes used to manipulate the voxels in a world, including special states.
Interfaces for non-voxel objects that can exist in a world, including all players, monsters, projectiles, etc.
Interfaces for various Minecart types.
Classes to facilitate world Structure generation.
The interfaces used when manipulating extra data can can be stored inside item stacks.
Classes related to creating or using structures without creating Structure blocks in the world.