Java比较日期对象

2024-04-13 07:48:04 24

日历，日期和LocalDate

JavaSE8

之前，之后，compareTo和equals方法

//日历和日期对象的使用    
final Date today = new Date();
final Calendar calendar = Calendar.getInstance();
calendar.set(1990, Calendar.NOVEMBER, 1, 0, 0, 0);
Date birthdate = calendar.getTime();

final Calendar calendar2 = Calendar.getInstance();
calendar2.set(1990, Calendar.NOVEMBER, 1, 0, 0, 0);
Date samebirthdate = calendar2.getTime();

//之前的例子
System.out.printf("Is %1$tF before %2$tF? %3$b%n", today, birthdate, Boolean.valueOf(today.before(birthdate)));
System.out.printf("Is %1$tF before %1$tF? %3$b%n", today, today, Boolean.valueOf(today.before(today)));
System.out.printf("Is %2$tF before %1$tF? %3$b%n", today, birthdate, Boolean.valueOf(birthdate.before(today)));

//之后的例子
System.out.printf("Is %1$tF after %2$tF? %3$b%n", today, birthdate, Boolean.valueOf(today.after(birthdate)));
System.out.printf("Is %1$tF after %1$tF? %3$b%n", today, birthdate, Boolean.valueOf(today.after(today)));
System.out.printf("Is %2$tF after %1$tF? %3$b%n", today, birthdate, Boolean.valueOf(birthdate.after(today)));

//比较例子
System.out.printf("Compare %1$tF to %2$tF: %3$d%n", today, birthdate, Integer.valueOf(today.compareTo(birthdate)));
System.out.printf("Compare %1$tF to %1$tF: %3$d%n", today, birthdate, Integer.valueOf(today.compareTo(today)));
System.out.printf("Compare %2$tF to %1$tF: %3$d%n", today, birthdate, Integer.valueOf(birthdate.compareTo(today)));

//平等的例子
System.out.printf("Is %1$tF equal to %2$tF? %3$b%n", today, birthdate, Boolean.valueOf(today.equals(birthdate)));
System.out.printf("Is %1$tF equal to %2$tF? %3$b%n", birthdate, samebirthdate,
            Boolean.valueOf(birthdate.equals(samebirthdate)));
System.out.printf(
            "Because birthdate.getTime() -> %1$d is different from samebirthdate.getTime() -> %2$d, there are millisecondes!%n",
            Long.valueOf(birthdate.getTime()), Long.valueOf(samebirthdate.getTime()));

//从日历中清除毫秒
calendar.clear(Calendar.MILLISECOND);
calendar2.clear(Calendar.MILLISECOND);
birthdate = calendar.getTime();
samebirthdate = calendar2.getTime();

System.out.printf("Is %1$tF equal to %2$tF after clearing ms? %3$b%n", birthdate, samebirthdate,
            Boolean.valueOf(birthdate.equals(samebirthdate)));

isBefore，isAfter，compareTo和equals方法

//使用LocalDate final LocalDate now = LocalDate.now(); final LocalDate birthdate2 = LocalDate.of(2012, 6, 30); final LocalDate birthdate3 = LocalDate.of(2012, 6, 30); //小时，分钟，秒和nanoOfsecond也可以与其他类LocalDateTime一起配置 //LocalDateTime.of（年，月，日，月，小时，分钟，秒，nanoOfSecond）； //isBefore示例 System.out.printf("Is %1$tF before %2$tF? %3$b%n", now, birthdate2, Boolean.valueOf(now.isBefore(birthdate2))); System.out.printf("Is %1$tF before %1$tF? %3$b%n", now, birthdate2, Boolean.valueOf(now.isBefore(now))); System.out.printf("Is %2$tF before %1$tF? %3$b%n", now, birthdate2, Boolean.valueOf(birthdate2.isBefore(now))); //isAfter示例 System.out.printf("Is %1$tF after %2$tF? %3$b%n", now, birthdate2, Boolean.valueOf(now.isAfter(birthdate2))); System.out.printf("Is %1$tF after %1$tF? %3$b%n", now, birthdate2, Boolean.valueOf(now.isAfter(now))); System.out.printf("Is %2$tF after %1$tF? %3$b%n", now, birthdate2, Boolean.valueOf(birthdate2.isAfter(now))); //compareTo示例 System.out.printf("Compare %1$tF to %2$tF %3$d%n", now, birthdate2, Integer.valueOf(now.compareTo(birthdate2))); System.out.printf("Compare %1$tF to %1$tF %3$d%n", now, birthdate2, Integer.valueOf(now.compareTo(now))); System.out.printf("Compare %2$tF to %1$tF %3$d%n", now, birthdate2, Integer.valueOf(birthdate2.compareTo(now))); //等于例子 System.out.printf("Is %1$tF equal to %2$tF? %3$b%n", now, birthdate2, Boolean.valueOf(now.equals(birthdate2))); System.out.printf("Is %1$tF to %2$tF? %3$b%n", birthdate2, birthdate3, Boolean.valueOf(birthdate2.equals(birthdate3))); //isEqual示例 System.out.printf("Is %1$tF equal to %2$tF? %3$b%n", now, birthdate2, Boolean.valueOf(now.isEqual(birthdate2))); System.out.printf("Is %1$tF to %2$tF? %3$b%n", birthdate2, birthdate3, Boolean.valueOf(birthdate2.isEqual(birthdate3)));

Java8之前的日期比较

在Java8之前，可以使用java.util.Calendar和java.util.Date类比较日期。Date类提供4种比较日期的方法：

after(Datewhen)

before(Datewhen)

compareTo(DateanotherDate)

equals(Objectobj)

after，before，compareTo和equals方法通过比较返回的值getTime()对于每个日期的方法。

compareTo方法返回正整数。

大于0的值：当Date在Date参数之后

大于0的值：当Date在Date参数之前

值等于0：当Date等于Date参数时

equals如示例中所示，结果可能令人惊讶，因为如果未明确给出值，则毫秒等值不会使用相同的值进行初始化。

从Java8开始

在Java8中，可以使用java.time.LocalDate使用Date的新对象。LocalDate实现ChronoLocalDate，它是可插入Chronology或日历系统的日期的抽象表示。

为了具有日期时间精度，必须使用对象java.time.LocalDateTime。LocalDate并LocalDateTime使用相同的方法名称进行比较。

使用a比较日期与使用a比较日期LocalDate是不同的，ChronoLocalDate因为不考虑年代或日历系统的第一个日期。

因为大多数应用程序都应使用LocalDate，ChronoLocalDate所以示例中未包含。在这里进一步阅读。

大多数应用程序应将方法签名，字段和变量声明为LocalDate，而不是this[ChronoLocalDate]接口。

LocalDate有5种比较日期的方法：

isAfter(ChronoLocalDateother)

isBefore(ChronoLocalDateother)

isEqual(ChronoLocalDateother)

compareTo(ChronoLocalDateother)

equals(Objectobj)

在的情况下，LocalDate参数，isAfter，isBefore，isEqual，equals和compareTo现在使用这种方法：

int compareTo0(LocalDate otherDate) {
    int cmp = (year - otherDate.year);
    if (cmp == 0) {
        cmp = (month - otherDate.month);
        if (cmp == 0) {
            cmp = (day - otherDate.day);
        }
    }
    return cmp;
}

equals方法检查参数引用是否首先等于日期而isEqual直接调用compareTo0。

如果是其他类别的实例，ChronoLocalDate则使用来比较日期EpochDay。时代天计数是天的简单递增计数，其中天0为1970-01-01(ISO)。