Why is an API gateway pattern recommended when deploying transformed Java modules that replace extracted COBOL services?

Think of it like working hands-on with IBM mainframe systems — the answer here is 'To convert Java method calls back into COBOL CALL statements for legacy compatibility'. An API gateway provides a stable interface that decouples callers from the underlying Java implementation, allowing legacy COBOL programs and external consumers to reach the new service without knowin. On real mainframe exams, this concept comes up repeatedly so make sure you have it locked in.