java.lang.ClassCastException：jdk.nashorn.internal.objects.NativeArray无法转换为java.lang.Comparable

Question

While running JavaScript with Nashorn

var jsArray = [7,4,1,8,3,2]; 
var list = java.util.Arrays.asList(jsArray);
java.util.Collections.sort(list);
list.forEach(function(el) { print(el) } ); 

i got

Exception in thread "main" java.lang.ClassCastException: jdk.nashorn.internal.objects.NativeArray cannot be cast to java.lang.Comparable
at java.util.Collections.sort(Collections.java:170)

So is the way to use Java Collections in JavaScript?

UPDATE:

Thanks to Attila, not both JS and JJS script produce the same output

var jsArray = [1,2,3,4]; 
jsArray.forEach(function(el) { print(el) } ); 


var jsArray = [1,2,3,4];
//var list = java.util.Arrays.asList(jsArray);
var list = Java.to(jsArray, Java.type('java.util.List'))
list.forEach(function(el) { print(el) } ); 

Answer 1

Using java.util.Arrays.asList will create an array with a single element being the JS array. JS arrays aren't Java arrays...

Instead of java.util.Arrays.asList , use Java.to(jsArray, Java.type('java.util.List')) . The resulting list will be backed by the JS array, so changes to one will be reflected by the other. You can also convert the JS array to a Java array with just Java.to(jsArray) (which is equivalent to Java.to(jsArray, Java.type('java.lang.Object[]') . So if you want to go through the array conversion step, you can use java.util.Arrays.asList(Java.to(jsArray)); .

In general, Nashorn will convert JS arrays to Java arrays automatically in most cases where the Java method signature specifies an array parameter, so you don't have to use Java.to() explicitly a lot. Arrays.asList(T...) is unfortunately a vararg method, so there's some ambiguity as to how to handle the argument.