Java：将集合类型转换为子类型 [英] Java: cast collection type to subtype

问题描述

假设类 B 扩展类 A 。我有一个列表< A> 我恰好知道只有包含 B 。是否有一种方法可以将 List 转换为列表< B> ？

Suppose class B extends class A. I have a List<A> that I happen to know only contains instances of B. Is there a way I can cast the List<A> to a List<B>?

看来我唯一的选择是迭代集合，在时间转换一个元素，创建一个新的集合。

It seems my only option is to iterate over the collection, casting one element at time, creating a new collection. This seems like an utter waste of resources given type erasure makes this completely unnecessary at run-time.

推荐答案

你可以通过未分类的列表界面：

You can cast through the untyped List interface:

List<A> a = new ArrayList<A>();
List<B> b = (List)a;

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