Do you mean the USER must remain after the objects are gone?

One way is to drop the user with the cascade option then recreate it. The other is to write some PL/SQL to identify and drop all the objects doing stuff like:

BEGIN
FOR cur_rec IN (SELECT object_type, object_name FROM user_objects) LOOP
BEGIN
EXECUTE IMMEDIATE 'DROP ' || cur_rec.object_type || ' ' || cur_rec.object_name;
EXCEPTION
WHEN OTHER THEN
NULL;
END;
END LOOP;
END;
/

This may need a bit of work as I've not got a server available to check it at the moment.

Cheers