尽管Oracle教程示例代码中显示了Java 8 Instant类没有plusHours方法

Question

Instant oneHourLater = Instant.now().plusHours(1);

null

InstantPrint.java:6: error: cannot find symbol
        Instant oneHourLater = Instant.now().plusHours(1);
                                            ^
  symbol:   method plusHours(int)
  location: class Instant

但是这个Java文档提到了plushours()方法，但是我检查了这个instant类，它不包含plushours()方法。

那么，为什么要在示例中提到这个plushours()方法呢？

Answer 1

不幸的是，Oracle教程在这个问题上是不正确的。那行示例代码完全是错误的。你接得好。

这个错误是非常不幸的，因为教程是学习和研究Java的很好的资源。

instant类没有在Java8或Java9中定义的plushours这样的方法。

Instant later = instant.plus( 1 , ChronoUnit.HOURS ) ;

ZoneId z = ZoneId.of( "America/Montreal" ) ;
ZonedDateTime zdt = instant.atZone( z ) ; // Same moment, but viewed through the lens of a region’s wall-clock time.
ZonedDateTime zdtLater = zdt.plusHours( 1 ) ;

// ZonedDateTime
LocalDate ld = LocalDate.of( 2017 , Month.MARCH , 12 ) ;
LocalTime lt = LocalTime.of( 1 , 0 ) ;
ZoneId z = ZoneId.of( "America/New_York" ) ;
ZonedDateTime zdt = ZonedDateTime.of( ld , lt , z ) ;
ZonedDateTime zdtOneHourLater = zdt.plusHours( 1 ) ;

System.out.println( "zdt: " + zdt ) ;
System.out.println( "zdtOneHourLater: " + zdtOneHourLater ) ; 
System.out.println( "Yikes! 1 AM plus an hour is 3 AM? Yes, that is an anomaly known as Daylight Saving Time (DST)." ) ;
System.out.println( "" ) ;

// Instant
Instant instant = zdt.toInstant() ;  // Adjust into UTC. Same moment, same point on the timeline, but viewed by a different wall-clock.
Instant instantOneHourLater = instant.plus( 1 , ChronoUnit.HOURS ) ;

System.out.println( "instant: " + instant ) ;
System.out.println( "instantOneHourLater: " + instantOneHourLater ) ;  
System.out.println( "Instant is always in UTC. So no anomalies, no DST. Adding an hour to 1 AM results in 2 AM every time." ) ;

请查看在ideone.com实时运行的代码。

ZDT:2017-03-12T01:00-05:00[美国/纽约]

ZdtoneHourlater:2017-03-12T03:00-04:00[美国/纽约]