A Java annotation that can be used on a method, M, that implements a
StreamBase Java custom function. The value of the annotation must be a String
whose value is the name of another method, R, in the same class as M.
Constraints on R's declaration:
- R must be public and static.
- R must take the same number of arguments as M.
- All of R's arguments must be of type
- R's return type must be CompleteDataType.
StreamBase calls R under one of the following circumstances:
- A custom function call passes one or more parameters of StreamBase type
List or Tuple.
- A custom function returns a value whose Java type is
- A custom function call matches multiple Java functions (e.g.,
calljava is called with a StreamBase long value and there are
two identically-named Java methods, one of which takes a Java long and
one of which takes a Java Long.
In these cases, StreamBase (as part of typechecking an application that calls
custom Java functions) calls each appropriate R, supplying CompleteDataType
values that describe the types of the actual parameters used in the custom
function call. R must return either:
- A CompleteDataType that describes the type of M's return value (note: the CompleteDataType must
be consistent with M's actual return type), or
null if M can not be called with actual parameters of the
specified types (e.g., because the schema of a tuple argument doesn't
match the function's requirements).