判斷當前時間為星期幾

 Calendar cal = Calendar.getInstance();
        int data=cal.get(Calendar.DAY_OF_WEEK);
        if(data==Calendar.MONDAY){
          System.out.println("周一");
        }else if (data==Calendar.TUESDAY){
            System.out.println("周二");
        }else if (data==Calendar.WEDNESDAY){
            System.out.println("周三");
        }else if (data==Calendar.THURSDAY){
            System.out.println("周四");
        }else if (data==Calendar.FRIDAY){
            System.out.println("周五");
        }else if (data==Calendar.SATURDAY){
            System.out.println("周六");
        }else if (data==Calendar.SUNDAY){
            System.out.println("周天");
        }