SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
        Date d1=sdf.parse("2017-9-5 10:10:10");  
        Date d2=sdf.parse("2017-9-4 11:11:11");  
        

        Calendar  calendar =Calendar.getInstance();//日曆類
	calendar.setTime(d2);
	double now_date =calendar.getTimeInMillis();
	calendar.setTime(d1);
	double overdue_time=calendar.getTimeInMillis();
	double overdueDate=(now_date-overdue_time)/(1000*3600*24); 
	System.out.println(overdueDate);
 

結果為：

 -0.9576273148148148

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