模糊的varargs方法调用编译错误

Question

method(1);  // This works -

void method(int... x) { }
void method(int x) { }  // - this method is called

If I add a varargs parameter to the second method, I get a "reference to method is ambiguous" compilation error:

method(1);  // This now fails

void method(int... x) { }
void method(int x, String... y) { }  // adding String... y causes a problem.

As the String... y argument(s) can be left "blank", why doesn't Java still pick that method? Thanks, and apologies if there is a closely matching explanation on SO; I did look for one.

Answer 1

The compiler always makes the choice to use the most specific method.

In the first case, because the number of the arguments exactly matches void method(int x) , it is the one that's being called.

In the second case, the number of the arguments don't match any case, and it can be called from both methods, resulting the ambiguity.

Check the JLS - 15.12.2. Compile-Time Step 2: Determine Method Signature for details.

Answer 2

The number of arguments can be 0 or many. which makes

void method(int x, String... y){ } is similar to void method(int x){}

And the

void method(int... x){} is also similar to void method(int x){}

If you call method(1), the compiler will find two applicable method to this call and raises and exception.