如何将列表从子类泛型转换为父类泛型? [英] How do I cast a List from a subclass generic to a parent class generic?

问题描述

我正在修改开放的JDK以添加功能，但是我两次都遇到了这种情况，但没有好的解决方案.

I'm modifying open JDK to add features and I've run into this twice with no good solution.

有一个名为JCStatement的类，该类扩展了JCTree.

There's a class named JCStatement which extends JCTree.

问题:我想将List<JCStatement>转换为List<JCTree>.

很明显，一个类可以引用其扩展名之一，但是当我将其放在List上时，它就是行不通的.

It's clear that a class can reference one of its extensions, but when I have it on a List, it just doesn't work.

我曾经使用过:(List<JCTree>)((List<?>)params)进行强制转换，但不能在ant上构建. IDE向我发出以下警告:

I used: (List<JCTree>)((List<?>)params) to cast, which works, but doesn't build on ant. IDE gives me the following warning:

Type safety: Unchecked cast from List<capture#1-of ?> to List<JCTree>

所以这必须以某种方式解决.

So this must be worked around somehow.

感谢您的帮助.

推荐答案

列表或一般类型的通用类型集合似乎是一个问题.

This seems to be an issue with the List, or generic types collections as general.

有史以来最简单的解决方案:

Simplest solution ever:

ListBuffer<JCTree> ls = new ListBuffer<JCTree>();
for(JCVariableDecl v : params){ ls.append(v); }
return ls.toList();

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