为什么不编译:List>lss = new ArrayList>();
问题描述：
以下代码:
List<List<String>> lss = new ArrayList<ArrayList<String>>();
导致此编译时错误:
Type mismatch: cannot convert from ArrayList<ArrayList<String>> to List<List<String>>
为了修复我将代码更改为:
to fix I change the code to :
List<ArrayList<String>> lss = new ArrayList<ArrayList<String>>();
为什么会抛出这个错误?这是因为 List 中的泛型类型 List 被实例化了，并且因为 List 是一个接口，所以这是不可能的吗?>
Why is this error being thrown ? Is this because the generic type List in List<List<String>> is instantiated and since List is an interface this is not possible ?
答
问题是泛型中的类型说明符不允许(除非你告诉它)允许子类.你必须完全匹配.
The problem is that type specifiers in generics do not (unless you tell it to) allow subclasses. You have to match exactly.
尝试:
List<List<String>> lss = new ArrayList<List<String>>();
或:
List<? extends List<String>> lss = new ArrayList<ArrayList<String>>();