The difference between "instanceof List" and 'o instanceof List<?>"
I don't see any difference in the following:
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
开发者_如何学Ccan't be used instead and vise versa?
No difference. The wildcard is erased at compile time.
According to this blog the answer is 'they are exactly the same':
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.
Object o = new ArrayList<String>();
List<?> list_string = (List)o; //same as (List<?>)o
boolean b = o instanceof List; //same as o instanceof List<?>
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