Forcing elements of List to be converted as java.lang.Long

Tim Fox timvolpe at
Wed Nov 26 23:37:11 UTC 2014

Hi Attila,

I understand the generic type info is erased, but my question was 
whether there is any way I can "force" Nashorn to convert the elements 
as Long rather than Integer when doing the conversion, e.g. using some 
special Nashorn specific syntax, e.g.

var arr = [123];
arr.forceConversionAsLong = true; // A contrived example but you get the 
point :);

(or whatever)

On 26/11/14 21:50, Attila Szegedi wrote:
> I don't think so. As the types are erased at run time all we see is a method with signature foo(List list). I think if you tried to add two methods to a class:
>      public void foo(List<Long> x) { }
>      public void foo(List<Integer> x) { }
> then javac would refuse to compile it saying that both have the same erasure.
> Attila.
> On Nov 26, 2014, at 10:45 PM, Tim Fox <timvolpe at> wrote:
>> Hello folks,
>> I have a Java method:
>> public void foo(List<Long> list) {
>>   System.out.println("elem0 is " + list.get(0));
>> }
>> Which I call from JS with a JS array:
>> This results in a ClassCastException as Nashorn converts the JS Array into a java.util.List instance which contains a java.lang.Integer element (not java.lang.Long)
>> Is there any way to force Nashorn to convert the array elements as Longs not Integers?
>> Thanks.

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