init() — The init() action is optional. If a custom aggregate function defines an init() action, it must take no arguments and must not return a value. The correlator executes the init() action once for each new aggregate function instance it creates in a stream query.

add() — A custom aggregate function must define an add() action. The add() action must take the same ordered set of arguments that are specified in the custom aggregate function signature. That is, the names, types, and order of the arguments must all be the same. The correlator executes the add() action once for each item added to the set of items that the aggregate function is operating on.

remove() — A bounded aggregate function must define a remove() action. An unbounded aggregate function must not define a remove() action. If you do not specify either bounded or unbounded, the remove() action is optional. The remove() action must take the same ordered set of arguments as the add() action and must not return a value. The correlator executes the remove() action once for each item that leaves the set of items that the aggregate function is operating on. The value that remove() is called with is the same value that add() was called with.

value() — All custom aggregate functions must define a value() action. The value() action must take no arguments and its return type must match the return type in the aggregate function signature. The correlator executes the value() action once per lot per aggregate function instance and returns the current aggregate value to the query.