@Override
    public String toString() {
        return "SessionWindows{" +
            "gapMs=" + gapMs +
            ", graceMs=" + graceMs +
            '}';
    }
Return the specified gap for the session windows in milliseconds.

@return the inactivity gap of the specified windows
streams/src/main/java/org/apache/kafka/streams/kstream/SessionWindows.java