oh this ?

[fukurou]

    public void open(int minutes) {
        Date now = new Date();
        openedGate = addMinutesToJavaUtilDate(now, minutes);
    }

in java it is an inferred this actually
so the program reads it as

    public void open(int minutes) {
        Date now = new Date();
        this.openedGate = addMinutesToJavaUtilDate(now, minutes);
    }