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Re: Why does Java complain if you cast a Map but not an Object?

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On 4/19/2023 2:19 PM, e.d.pro...@gmail.com wrote:
> On Wednesday, April 19, 2023 at 1:43:39 PM UTC-4, Arne Vajhøj wrote:
> 
>> System.out.println(test2(a2)); 
>> System.out.println(test2(a2).get(0).substring(0, 1));
> 
> So no warnings about casting one thing to another possibly compatible
> thing (Object to String) because the cast immediately throws
> exception if Object is not a String, but using containers (List, Map)
> it warns because the cast hides the error; it actually allows
> incompatible casting (List<Integer> to List<String>) and can print
> the resulting object, and crashes when you try to return an element
> into a typed variable. Of course we don't need to worry about
> immediate casting exceptions because it's Runtime. If you take a
> List<Integer> and cast it to a List<String>, you can call get(idx)
> and return the value into a variable declared as String and crash
> (but it compiles). If you return the value into a variable declared
> as Object, it works, so when you called .get(0) it didn't care that
> it wasn't a String until it tried to process the .substring. As long
> as you treat that result as Object, it's fine. 
> System.out.println(test2(a2).get(0).getClass()); // List<String>
> doesn't care that element is Integer

Yes. That is how I see it all work.

Arne

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Why does Java complain if you cast a Map but not an Object? "e.d.pro...@gmail.com" <e.d.programmer@gmail.com> - 2023-04-19 08:16 -0700
  Re: Why does Java complain if you cast a Map but not an Object? Arne Vajhøj <arne@vajhoej.dk> - 2023-04-19 13:43 -0400
    Re: Why does Java complain if you cast a Map but not an Object? "e.d.pro...@gmail.com" <e.d.programmer@gmail.com> - 2023-04-19 11:19 -0700
      Re: Why does Java complain if you cast a Map but not an Object? Arne Vajhøj <arne@vajhoej.dk> - 2023-04-19 15:23 -0400
        Re: Why does Java complain if you cast a Map but not an Object? Michael Jung <miju@golem.phantasia.org> - 2023-04-23 14:30 +0200

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