Var-args overloading

Question

Could anyone please explain why this code throws an ambiguous overload error, surely the Integer method is more specific and applicable?

Thanks,

Ned

package object_orientation;
public class Ambiguous {
    //ambiguous error compiler unsure whether boxing is needed or not
    static void overload(Integer... d){
        System.out.println("Integer");
    }

    static void overload(long... d){
        System.out.println("Long");
    }

    public static void main(String a[]){
        int i = 1;
        overload(i);
    }
}

see that `Integer` is different from `int`. `Integer` is a wrapper. — fpe, Aug 19 '13 at 13:05
good post on this - http://stackoverflow.com/questions/2521293/bug-with-varargs-and-overloading — Zack Macomber, Aug 19 '13 at 13:08
if you change `long...` to `long` in your overload method, it will compile. I believe varargs translate to being an array at compile time so I think that's where the ambiguity is happening — Zack Macomber, Aug 19 '13 at 13:11

JNL · Accepted Answer · 2013-08-19T13:22:22.583

3

These concepts in Java should help, Boxing + Widening is allowed, but not Widening + Boxing.

These rules of Widening, Boxing and Vararg should help:

Primitive Widening > Boxing > Varargs.

Widening and Boxing (WB) not allowed.

Boxing and Widening (BW) allowed.

While overloading, Widening + vararg and Boxing + vararg can only be used in a mutually exclusive manner

Widening between wrapper classes not allowed.

Widening+varArgs & Boxing+varargs are individually allowed (but not allowed in overloaded version of method).

Boxing+Widening is preferred over Boxing+Varargs.

Hope this helps.

edited Aug 19 '13 at 13:22

answered Aug 19 '13 at 13:12

JNL

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Thanks. I thought the int would simply be boxed and applied to the Integer var-args and the long var-args ignored, because you can't widen and box at the same time. The compiler tells me I have an Ambiguous error of type Ambiguous – Xivilai Aug 19 '13 at 14:16

Var-args overloading

1 Answers1