问题
This question already has an answer here:
- Arrays.asList() not working as it should? 10 answers
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?
回答1:
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.
回答2:
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)
回答3:
Arrays.asList() takes a arbitrary number of arguments of given type T (#asList(T.. t)). Calling Arrays.asList(arrs) what you really do is passing single element of type int[] hence the problem.
It should be either:
int[] arrs = {1,2,4,3,5,6};List<int[]> arry = Arrays.asList(arrs);
or
List<Integer> arry = Arrays.asList(1,2,3,4,5,6);
来源：https://stackoverflow.com/questions/20912313/why-does-auto-boxing-and-unboxing-of-integers-does-not-work-with-arrays-aslist-i