什么是Java中的魔法值？

 /**
     * 获取当前周所有的日期
     *
     * @return
     */
    public static List<String> getRangeDayOfWeek() {
        List<String> list = new ArrayList<>();
        // 日期格式转换
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        // 时间调整到本周一
        Calendar instance = Calendar.getInstance();
        instance.set(instance.get(Calendar.YEAR), instance.get(Calendar.MONDAY), instance.get(Calendar.DAY_OF_MONTH), 0, 0, 0);
        instance.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
        //循环打印
        for (int i = 1; i <= 7; i++) {
            list.add(sdf.format(instance.getTime()));
            instance.add(Calendar.DAY_OF_WEEK, 1);
        }
        return list;
    }

static final int WEEK_DAYS= 7;