All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`addUserToGroup(String user, String group)`
`void`	`createGroup(String group)`
`Set<String>`	`getAllGroups()`
`Set<String>`	`getGroupsForUser(String user)`
`Set<String>`	`getUsersInGroup(String group)`
`void`	`removeGroup(String group)`
`void`	`removeUserFromGroup(String user, String group)`

Set<String> getUsersInGroup(String group)

void addUserToGroup(String user,
                    String group)

void removeUserFromGroup(String user,
                         String group)

Set<String> getGroupsForUser(String user)

Interface GroupDatabase