Calendar c = Calendar.getInstance();
c.set(2017, 11, 5, 0, 0, 0);
System.out.println(c.getTimeInMillis());
1512403200742
此种方式生成后,毫秒数不为0
Calendar c = Calendar.getInstance();
c.set(2017, 11, 5, 0, 0, 0);
c.set(Calendar.MILLISECOND, 0);
System.out.println(c.getTimeInMillis());
1512403200000
此方式生成毫秒为0
原因:Calendar用当前时间进行的初始化