详解在java中进行日期时间比较的4种方法

@Test
void testDateCompare() throws ParseException {
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
 Date date1 = sdf.parse("2009-12-31");
 Date date2 = sdf.parse("2019-01-31");

 System.out.println("date1 : " + sdf.format(date1));
 System.out.println("date2 : " + sdf.format(date2));

 if (date1.compareTo(date2) > 0) {
  System.out.println("Date1 时间在 Date2 之后");
 } else if (date1.compareTo(date2) < 0) {
  System.out.println("Date1 时间在 Date2 之前");
 } else if (date1.compareTo(date2) == 0) {
  System.out.println("Date1 时间与 Date2 相等");
 } else {
  System.out.println("程序怎么会运行到这里?正常应该不会");
 }
}

@Test
void testDateCompare2() throws ParseException {
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
 Date date1 = sdf.parse("2009-12-31");
 Date date2 = sdf.parse("2019-01-31");

 System.out.println("date1 : " + sdf.format(date1));
 System.out.println("date2 : " + sdf.format(date2));

 if (date1.after(date2)) {
  System.out.println("Date1 时间在 Date2 之后");
 }

 if (date1.before(date2)) {
  System.out.println("Date1 时间在 Date2 之前");
 }

 if (date1.equals(date2)) {
  System.out.println("Date1 时间与 Date2 相等");
 }
}

@Test
void testDateCompare3() throws ParseException {
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
 Date date1 = sdf.parse("2009-12-31");
 Date date2 = sdf.parse("2019-01-31");

 System.out.println("date1 : " + sdf.format(date1));
 System.out.println("date2 : " + sdf.format(date2));

 Calendar cal1 = Calendar.getInstance();
 Calendar cal2 = Calendar.getInstance();
 cal1.setTime(date1);
 cal2.setTime(date2);

 if (cal1.after(cal2)) {
  System.out.println("Date1 时间在 Date2 之后");
 }

 if (cal1.before(cal2)) {
  System.out.println("Date1 时间在 Date2 之前");
 }

 if (cal1.equals(cal2)) {
  System.out.println("Date1 时间与 Date2 相等");
 }
}

@Test
void testDateCompare4() throws ParseException {
 DateTimeFormatter sdf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
 LocalDate date1 = LocalDate.of(2009, 12, 31);
 LocalDate date2 = LocalDate.of(2019, 1, 31);

 System.out.println("date1 : " + sdf.format(date1));
 System.out.println("date2 : " + sdf.format(date2));

 System.out.println("Is...");
 if (date1.isAfter(date2)) {
  System.out.println("Date1 时间在 Date2 之后");
 }

 if (date1.isBefore(date2)) {
  System.out.println("Date1 时间在 Date2 之前");
 }

 if (date1.isEqual(date2)) {
  System.out.println("Date1 时间与 Date2 相等");
 }
}