为什么java.sql.Timestamp扩展java.util.Date [英] Why does java.sql.Timestamp extend java.util.Date

问题描述

当我看到这个时，我感到困惑:

When I saw this I got baffled:

  public class Timestamp extends java.util.Date {
    //...
    public boolean equals(java.lang.Object ts) {
      if (ts instanceof Timestamp) {
        return this.equals((Timestamp)ts);
      } else {
        return false;
      }
    }
    public int hashCode() {
        return super.hashCode();
    }

它确实以粗体Note记录在案 (请参见 https://docs.oracle.com/javase/7/docs/api/java/sql/Timestamp.html )

It is indeed documented with a bold Note (see https://docs.oracle.com/javase/7/docs/api/java/sql/Timestamp.html)

对我来说，做出如此糟糕的决定可能是什么原因? 与java.util.Date对象进行比较时，为什么不调用super.equals(this)以使相等比较对称?

What could be the cause to make such a, to me, very bad decision? Why not call super.equals(this) when compared to a java.util.Date object to make the equal comparison symmetrical?

推荐答案

相反，请使用java.time

正如其他人所述:

Instead, use java.time

As others stated:

• 此类的继承设计不佳，存在缺陷.
• 现在该类已经成为历史遗产，由避免在java.time包之外找到所有旧的旧式日期时间类.

  Avoid all the old legacy date-time classes found outside the java.time package.

  对于数据库，请使用符合 JDBC 4.2或更高版本的驱动程序直接与数据库交换java.time对象.您可以忘记有关java.sql.Timestamp的全部信息.

  For databases, use a driver compliant with JDBC 4.2 or later to directly exchange java.time objects with your database. You can forget all about java.sql.Timestamp.

  存储:

  Instant instant = Instant.now() ;
  myPreparedStatement.setObject( … , instant ) ;
  

  检索:

  Instant instant = myResultSet.getObject( … , Instant.class ) ;
  

  ---

  关于java.time

  java.time 框架已内置在Java 8及更高版本中.这些类取代了麻烦的旧版日期时间类，例如 SimpleDateFormat .

  ---

  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.

  Joda-Time 项目，现在位于

  The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

  要了解更多信息，请参见 Oracle教程.并在Stack Overflow中搜索许多示例和说明.规范为 JSR 310 .

  To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

  在哪里获取java.time类?

  Where to obtain the java.time classes?

  • Java SE 8 ， Java SE 9 和更高版本
    • 内置.
    • 具有捆绑的实现的标准Java API的一部分.
    • Java 9添加了一些次要功能和修复.
    • Java SE 8, Java SE 9, and later
      • Built-in.
      • Part of the standard Java API with a bundled implementation.
      • Java 9 adds some minor features and fixes.
      • 许多java.time功能都向后移植到Java 6& 7在> ThreeTen-Backport 中./li>
      • > ThreeTenABP 项目适应了<专门用于Android的em> ThreeTen-Backport (上面提到).
      • 请参见 如何使用ThreeTenABP… .
      • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
      • See How to use ThreeTenABP….

      > ThreeTen-Extra 项目扩展了java.time与其他班级.该项目为将来可能在java.time中添加内容提供了一个试验场.您可能会在这里找到一些有用的类，例如 Interval ， YearWeek ， YearQuarter 和更多.

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