Java 計算兩個日期相差天數

import java.util.Calendar;

public class CalendarTest2 {
	public static void main(String[] args) {
		
		//計算兩個日期相差天數
		Calendar c1=Calendar.getInstance();
		c1.set(2018, 12-1,12);
		Calendar c2=Calendar.getInstance();
		c2.set(2018, 12-1,17);
		long t1=c1.getTimeInMillis();
		long t2=c2.getTimeInMillis();
		long days=(t2-t1)/(24*60*60*1000);
		System.out.println(days);
	}
}