The following is throws compile error
:
int[] arrs = {1,2,4,3,5,6};
List<Integer> arry = Arrays.asList(arrs);
but this works:
for (Integer i : arrs){
//do something
}
Auto-boxing works in many contexts, I just gave one example of for-loop
above. but it fails in the List-view
that I make in Arrays.asList()
.
Why does this fail and why is such as a design implementation chosen?
To make things work you need to use Integer[]
instead of int[]
.
Argument of asList
is of type T...
and generic types T
can't represent primitive types int
, so it will represent most specific Object class, which in this case is array type int[]
.
That is why Arrays.asList(arrs);
will try to return List<int[]>
instead of List<int>
or even List<Integer>
.
Some people expect automatic conversion from int[]
to Integer[]
, but lets nor forget that autoboxing works only for primitive types, but arrays are not primitive types.
The Arrays.asList
takes generic T[]
as argument. This T
is always an object, not a primitive. When you give an int[]
as parameter (not an array of objects but primitives) it'll think the argument is actually the first element of the vararg. So the resulting list will have the fingerprint List<int[]>
instead.
If you want to learn more about generics in Arrays, please read this page: http://docs.oracle.com/javase/tutorial/extra/generics/fineprint.html (part: Arrays)
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With