“警告:[未经检查]未经检查的演员表"将 Object 转换为 ArrayList<String[]> 时 [英] &quot;Warning: [unchecked] unchecked cast&quot; when casting Object to ArrayList&lt;String[]&gt;

问题描述

奇怪的情况 - 下面是代码:

Strange situation - below is the code:

ArrayList<String[]> listArr = new ArrayList<>();
Object[] obj = new Object[]{"str", listArr};

String str = (String) obj[0];//OK
ArrayList<String[]> list = (ArrayList<String[]>) obj[1];//warning: [unchecked] unchecked cast

构建项目时(在项目属性中使用编译器选项 -Xlint:unchecked)，我收到一个警告:

When project is built (with compiler option -Xlint:unchecked in project properties), I get one warning:

警告:[未选中]未选中的演员
ArrayList list = (ArrayList) obj[1];
需要:ArrayList
找到:对象

warning: [unchecked] unchecked cast
ArrayList list = (ArrayList) obj[1];
required: ArrayList
found: Object

但是以同样的方式转换 String 是可以的.这里有什么问题?

But casting String in the same way is OK. What is the problem here?

推荐答案

这是因为编译器无法在列表级别验证内部类型，所以需要先验证列表.和内部类型单独.

This is because the compiler can not verify the internal types at the list level, so you need to first verify for list. And the internal types individually.

代替 ArrayListlist = (ArrayList) obj[1];

应该是ArrayListlist = (ArrayList) obj[1];

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