Java - 列表强制转换以能够使用 addAll 函数 [英] Java - List cast to be able to use addAll function

问题描述

假设我有一个调用某个方法的实体

Supposed I have an entity that invokes some method

Object methodVal = ety.getClass().getMethod("someMethod").invoke(ety);

我的目标是将其转换为 List 以便使用 addAll 之类的功能，所以我尝试了

My goal is to cast it to List in order to user the function like addAll, so I tried

List.class.cast(methodVal).addAll((Collection<?>) Objects.requireNonNull(someValue)); 

//someValue is an Object and I cast it to Collection<?>)

代码运行良好，应用程序仍然可以运行，但是我收到一条警告

The code is working fine and the app is still can run, however I'm getting a warning saying

Unchecked call to 'addAll(Collection<? extends E>)' as a member of raw type 'java.util.List'

我也试过了

((List<?>) methodVal).addAll((Collection<?>) Objects.requireNonNull(someValue));

但是我收到一个错误说

Required type: Collection <? extends capture of ?>
Provided: Collection <capture of ?>

知道如何修复警告/错误吗?谢谢

Any idea on how can I fix the warning / error? Thanks

推荐答案

只显示未检查赋值的警告，不要使用原始类型.

Just suppress the warning about unchecked assignment, and don't use raw types.

或者注释方法:

@SuppressWarnings("unchecked")
void myMethod() {
    // ... code here ...

    ((List<Object>) methodVal).addAll((Collection<?>) Objects.requireNonNull(someValue));

    // ... code here ...
}

或者分配给一个局部变量并在那里注释:

Or assign to a local variable and annotate there:

@SuppressWarnings("unchecked")
List<Object> list = (List<Object>) methodVal;

list.addAll((Collection<?>) Objects.requireNonNull(someValue));

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