List< Long>对具有BigInteger值的ArrayList的引用 [英] How can a List<Long> references to an ArrayList which has BigInteger values
问题描述
此方法在JpaRepository中定义，并运行本机PostgreSQL查询。
This method is defined in a JpaRepository and runs a native PostgreSQL query.
List<Long> distributorIds = distributorRepository
.findDistributorIdsWithChildren(distributorId)
它无例外运行，并且在运行时，我在返回的distributorIds ArrayList中看到BigInteger值，而不是Long值。
与以下问题相同： Spring Data JPA中的错误：Spring Data返回List< BigInteger>而不是List< Long>
那么该错误怎么发生？我的意思是 JAVA如何允许这种操作？如果Java不检查这种类型错误，那不是JAVA中的泛型问题。
So how can this bug occur? I mean how JAVA allows this? If Java doesn't check this kind of type errors isn't it a problem with generics in JAVA.
注意：我还检查了Long和BigInteger的类型层次结构，
Note: I also checked the type hierarchy for Long and BigInteger and there is no sub/super class relation.
推荐答案
泛型类型检查是编译时的功能。在运行时，所有类型信息都会丢失。请参阅类型擦除。例如，如果将使用非泛型集合的旧版API映射到使用泛型且需要强制转换集合的API，则您看到的行为很容易发生。不幸的是，如果该集合包含意外类型的对象，您将只能在运行时找到它。
Generic type checks are a compile time feature. At runtime all type information is lost. See "type erasure". The behavior you see can easily happen if, for example, a legacy API that uses non-generic collections is mapped to an API that uses generics and requires a cast of the collection. If that collection happens to contain objects of an unexpected type you will, sadly, only find out at runtime.
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