doc/modules/cassandra/examples/CQL/create_function.cql

CREATE OR REPLACE FUNCTION somefunction(somearg int, anotherarg text, complexarg frozen<someUDT>, listarg list)
    RETURNS NULL ON NULL INPUT
    RETURNS text
    LANGUAGE java
    AS $$
        // some Java code
    $$;

CREATE FUNCTION IF NOT EXISTS akeyspace.fname(someArg int)
    CALLED ON NULL INPUT
    RETURNS text
    LANGUAGE java
    AS $$
        // some Java code
    $$;