为什么instanceof运算符允许使用无界通配符类型，但不允许Java中的其他参数化类型？
我认为，由于输入删除，使用 instanceof 和 class literals 不允许用于参数化泛型$ c>，除无界通配符类型。为什么Java语言设计者允许这种异常？对于无界通配符类型，没有类型擦除的作用？
I think due to type erasure , using instanceof and class literals are not allowed for parameterized generic types except unbounded wild card types . Why did the Java language designers allowed this exception ? There isn't any role of type erasure for unbounded wild card types ?
关键是对象知道它的具体类 - 但不是泛型类型的参数。所以如果我们构造一个 ArrayList< Integer> ，它知道在执行时它是一些 ArrayList kind - 但它不知道整数部分。
The point is that an object knows its concrete class - but not the generic type arguments for that. So if we construct an ArrayList<Integer>, that knows at execution time that it's an ArrayList of some kind - but it doesn't know about the Integer part.
ArrayList 某种部分恰恰是 ArrayList 的意思，这就是为什么：
The "ArrayList of some kind" part is precisely what ArrayList<?> means, which is why:
if (foo instanceof ArrayList<?>)
有效。这与使用原始类型相同：
is valid. It's just equivalent to using the raw type:
if (foo instanceof ArrayList)