“instanceof List”和“o instanceof List>”之间的区别

I don't see any difference in the following:

我看不出有什么区别:

    Object o = new LinkedList<Long>();

    System.out.println(o instanceof List); 
    System.out.println(o instanceof List<?>);

Is there any practical use of instanceof List<?> when instanceof List can't be used instead and vise versa?

是否有实用的instanceof列表

2 个解决方案

#1

No difference. The wildcard is erased at compile time.

没有区别。在编译时，通配符将被删除。

#2

According to this blog the answer is 'they are exactly the same':

根据这个博客，答案是“他们完全一样”:

as javac forbids instanceof expressions whose target type is a generic type; for casts, the compiler is slightly more permissive since casts to generic type are allowed but a warning is issued (see above). Anyway, the raw type should be replaced by an unbounded wildcard, as they have similar properties w.r.t. subtyping.

由于javac禁止instanceof表达式，其目标类型是泛型类型;对于类型转换，编译器会稍微宽容一些，因为对泛型类型的转换是允许的，但是会发出警告(见上面)。无论如何，原始类型应该被一个未绑定的通配符替换，因为它们有类似的属性w.r.t subtyping。

Object o = new ArrayList<String>();
List<?> list_string = (List)o; //same as (List<?>)o
boolean b = o instanceof List; //same as o instanceof List<?>

#1