Java:为什么不推荐使用 Date 构造函数，我用什么代替? [英] Java: Why is the Date constructor deprecated, and what do I use instead?
问题描述
我来自 C# 世界，所以对 Java 还不太熟悉.Eclipse 刚刚告诉我 Date 已被弃用:
Person p = new Person();p.setDateOfBirth(new Date(1985, 1, 1));为什么?应该使用什么(尤其是在上述情况下)代替?
tl;dr
LocalDate.of( 1985 , 1 , 1 )……或……
LocalDate.of( 1985 , Month.JANUARY , 1 )详情
java.util.Date、java.util.Calendar 和 java.text.SimpleDateFormat 类在 Java首先推出和发展.这些课程没有很好地设计或实施.尝试了改进，因此您发现了弃用.不幸的是，改进的尝试在很大程度上失败了.您应该完全避免这些类.它们在 Java 8 中被新类取代.
代码中的问题
java.util.Date 具有日期和时间部分.您忽略了代码中的时间部分.因此 Date 类将采用 JVM 的默认时区定义的一天的开始，并将该时间应用于 Date 对象.因此，您的代码的结果将根据它运行的机器或设置的时区而有所不同.可能不是你想要的.
如果您只需要日期而不需要时间部分，例如生日，您可能不想使用 Date 对象.您可能只想以
I come from the C# world, so not too experienced with Java yet. I was just told by Eclipse that Date was deprecated:
Person p = new Person();
p.setDateOfBirth(new Date(1985, 1, 1));
Why? And what (especially in cases like above) should be used instead?
tl;dr
LocalDate.of( 1985 , 1 , 1 )
…or…
LocalDate.of( 1985 , Month.JANUARY , 1 )
Details
The java.util.Date, java.util.Calendar, and java.text.SimpleDateFormat classes were rushed too quickly when Java first launched and evolved. The classes were not well designed or implemented. Improvements were attempted, thus the deprecations you’ve found. Unfortunately the attempts at improvement largely failed. You should avoid these classes altogether. They are supplanted in Java 8 by new classes.
Problems In Your Code
A java.util.Date has both a date and a time portion. You ignored the time portion in your code. So the Date class will take the beginning of the day as defined by your JVM’s default time zone and apply that time to the Date object. So the results of your code will vary depending on which machine it runs or which time zone is set. Probably not what you want.
If you want just the date, without the time portion, such as for a birth date, you may not want to use a Date object. You may want to store just a string of the date, in ISO 8601 format of YYYY-MM-DD. Or use a LocalDate object from Joda-Time (see below).
Joda-Time
First thing to learn in Java: Avoid the notoriously troublesome java.util.Date & java.util.Calendar classes bundled with Java.
As correctly noted in the answer by user3277382, use either Joda-Time or the new java.time.* package in Java 8.
Example Code in Joda-Time 2.3
DateTimeZone timeZoneNorway = DateTimeZone.forID( "Europe/Oslo" );
DateTime birthDateTime_InNorway = new DateTime( 1985, 1, 1, 3, 2, 1, timeZoneNorway );
DateTimeZone timeZoneNewYork = DateTimeZone.forID( "America/New_York" );
DateTime birthDateTime_InNewYork = birthDateTime_InNorway.toDateTime( timeZoneNewYork );
DateTime birthDateTime_UtcGmt = birthDateTime_InNorway.toDateTime( DateTimeZone.UTC );
LocalDate birthDate = new LocalDate( 1985, 1, 1 );
Dump to console…
System.out.println( "birthDateTime_InNorway: " + birthDateTime_InNorway );
System.out.println( "birthDateTime_InNewYork: " + birthDateTime_InNewYork );
System.out.println( "birthDateTime_UtcGmt: " + birthDateTime_UtcGmt );
System.out.println( "birthDate: " + birthDate );
When run…
birthDateTime_InNorway: 1985-01-01T03:02:01.000+01:00
birthDateTime_InNewYork: 1984-12-31T21:02:01.000-05:00
birthDateTime_UtcGmt: 1985-01-01T02:02:01.000Z
birthDate: 1985-01-01
java.time
In this case the code for java.time is nearly identical to that of Joda-Time.
We get a time zone (ZoneId), and construct a date-time object assigned to that time zone (ZonedDateTime). Then using the Immutable Objects pattern, we create new date-times based on the old object’s same instant (count of nanoseconds since epoch) but assigned other time zone. Lastly we get a LocalDate which has no time-of-day nor time zone though notice the time zone applies when determining that date (a new day dawns earlier in Oslo than in New York for example).
ZoneId zoneId_Norway = ZoneId.of( "Europe/Oslo" );
ZonedDateTime zdt_Norway = ZonedDateTime.of( 1985 , 1 , 1 , 3 , 2 , 1 , 0 , zoneId_Norway );
ZoneId zoneId_NewYork = ZonedId.of( "America/New_York" );
ZonedDateTime zdt_NewYork = zdt_Norway.withZoneSameInstant( zoneId_NewYork );
ZonedDateTime zdt_Utc = zdt_Norway.withZoneSameInstant( ZoneOffset.UTC ); // Or, next line is similar.
Instant instant = zdt_Norway.toInstant(); // Instant is always in UTC.
LocalDate localDate_Norway = zdt_Norway.toLocalDate();
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes. Hibernate 5 & JPA 2.2 support java.time.
Where to obtain the java.time classes?
- Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
- Java 9 brought some minor features and fixes.
- Java SE 6 and Java SE 7
- Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
- Android
- Later versions of Android (26+) bundle implementations of the java.time classes.
- For earlier Android (<26), the latest Android tooling enables a process known as API desugaring to provide a subset of the java.time functionality not originally built into Android.
- If the desugaring does not offer what you need, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above) to Android. See How to use ThreeTenABP….
这篇关于Java:为什么不推荐使用 Date 构造函数，我用什么代替?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
