Variable arguments

[Song Guo]

public class Varargs {
    public static void test(float a, Character... c) {
        System.out.println("float, Character...");
    }
    public static void test(Character... c) {
        System.out.println("Character...");
    }

    public static void main(String[] args) {
        test(1, 'a');
        test('a', 'b'); // compiling-time error                                                
    }
}

The 11th line is compiling error, but the 10th line is OK, why ? How does the compiler understanding them ? Thank you !

[Matthew Brown]

And what is the compile time error? Tell us the details - it makes life much easier for all of us.

[Song Guo]

Matthew Brown wrote:And what is the compile time error? Tell us the details - it makes life much easier for all of us.

The following Screenshot:

[Matthew Brown]

OK, you get that error when there are two different methods that match the call, and the compiler has no rule to determine the priority.

The key point here are:
- 1 is an int. This can automatically be converted to a float. It can't be autoboxed to a Character.
- 'a' is a char, which is an integer type. Which means it can be autoboxed to a Character, but it can also be converted to a float.

This means that line 10 can match test(float, Character...), but it can't match test(Character...), because 1 can't match Character. So there's no ambiguity.

However, line 11 can match both. At this point the compiler checks its rules for prioritising. These can get a bit complicated (read the Java Language Specification for the full rules), but it turns out that none of them can be applied in this case. So the compiler doesn't know what to do, and you get the error.

[Song Guo]

Matthew Brown wrote:OK, you get that error when there are two different methods that match the call, and the compiler has no rule to determine the priority.

The key point here are:
- 1 is an int. This can automatically be converted to a float. It can't be autoboxed to a Character.
- 'a' is a char, which is an integer type. Which means it can be autoboxed to a Character, but it can also be converted to a float.

This means that line 10 can match test(float, Character...), but it can't match test(Character...), because 1 can't match Character. So there's no ambiguity.

However, line 11 can match both. At this point the compiler checks its rules for prioritising. These can get a bit complicated (read the Java Language Specification for the full rules), but it turns out that none of them can be applied in this case. So the compiler doesn't know what to do, and you get the error.

Thank you very much, I understand.

[Matthew Brown]

You're welcome.