Thanks for the reference Marshall,
Try this code:
public static void main(String[] args) {
List<Number> tokens = new ArrayList<>();
tokens.add(3);
tokens.set(0, 4);
ArrayList<? super Number> generalize = (ArrayList<? super Number>) tokens;
// Upcasts all to number
Number n = 5;
generalize.set(0, n); // ok
var x = generalize.get(0); // ok
// n = generalize.get(0); // compile error
System.out.println(tokens.get(0)); // ok prints 5
x = tokens.get(0); // ok
n = tokens.get(0); // ok
List unknown = tokens; // warning
unknown.set(0, "foo"); // warning
// String t = tokens.get(0); // compile error
// String t = (String) tokens.get(0); // compile error
System.out.println(tokens.get(0)); // ok prints "foo"
n = tokens.get(0); // throws ClassCastException
}
> In fact, there's no cast I could figure out to make "generalize.set" work at
> all, except by changing its definition to use ArrayList (bare with no generic
> argument):
>
> ArrayList generalize = (ArrayList<? extends Number>) tokens; //compiles
> with
> warnings,
> generalize.set(0, 7); // works at runtime
I thought we can do a upcast and use <? super FeatureStructure> which gets
around the set problem you found but it looks like there are problems on the
get side...
The use of var is possible to get around the immediate errors but that is Java
10+
Moved the example to get the runtime error at the end
The run time exception comes in the get() call and setting it to the generic
type. (
Hai-Son
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