Overloading with Boxing and Var-args

[Jia Ramharai]

Hello All,
Can you please help on the following 2 code snippets?

public class BoxOrVararg {

	static void go(Byte x, Byte y) {
		System.out.println("Byte, Byte");
	}

	static void go(byte... x) {
		System.out.println("byte...");
	}

	public static void main(String[] args) {
		byte b = 5;
		go(b, b);
	}

}

Output:
Byte, Byte
Because widening beats var-args

public class BoxOrVararg {

	static void go(Integer x, Integer y) {
		System.out.println("Byte, Byte");
	}

	static void go(byte... x) {
		System.out.println("byte...");
	}

	public static void main(String[] args) {
		byte b = 5;
		go(b, b);
	}

}

Output:
byte...
???

Why doesn't widening take place instead of var-args?

Thank you.

[Richard Hayward]

Hi Jia,

Jia Ramharai wrote:

public class BoxOrVararg {

	static void go(Byte x, Byte y) {
		System.out.println("Byte, Byte");
	}

	static void go(byte... x) {
		System.out.println("byte...");
	}

	public static void main(String[] args) {
		byte b = 5;
		go(b, b);
	}

}

Output:
Byte, Byte
Because widening beats var-args

This example does not demonstrate that widening beats var-args.
It shows that boxing beats var-args.

Jia Ramharai wrote:

public class BoxOrVararg {

	static void go(Integer x, Integer y) {
		System.out.println("Byte, Byte");
	}

	static void go(byte... x) {
		System.out.println("byte...");
	}

	public static void main(String[] args) {
		byte b = 5;
		go(b, b);
	}

}

Output:
byte...
???

Why doesn't widening take place instead of var-args?

It's not just widening that would be required.
There would have to be a widening from byte to integer, followed by boxing to Integer.
Seems this is asking too much of the compiler (K&B p252).

Regards
Richard

[Zhenyi Luo]

Jia Ramharai wrote:Hello All,
Can you please help on the following 2 code snippets?

public class BoxOrVararg {

	static void go(Byte x, Byte y) {
		System.out.println("Byte, Byte");
	}

	static void go(byte... x) {
		System.out.println("byte...");
	}

	public static void main(String[] args) {
		byte b = 5;
		go(b, b);
	}

}

Output:
Byte, Byte
Because widening beats var-args

public class BoxOrVararg {

	static void go(Integer x, Integer y) {
		System.out.println("Byte, Byte");
	}

	static void go(byte... x) {
		System.out.println("byte...");
	}

	public static void main(String[] args) {
		byte b = 5;
		go(b, b);
	}

}

Output:
byte...
???

Why doesn't widening take place instead of var-args?

Thank you.

Because WidenAndBox is not allowed. On the other hand, though BoxAndWiden is allowed, trying to widen Byte to Integer will fail. Neither of them works.

[Jia Ramharai]

Thank you all for your replies