Var Arguments

[San Daida]

Hi All,

Could you please clarify my doubts related to below question

 
class VarArgsTest 
{
	
	public static void main(String[] args) 
	{
		System.out.println("Hello World!");
		VarArgsTest vat=new VarArgsTest();
		vat.doArgs(1);
		vat.doArgs(1,2);
		vat.doArgs(new Integer(1));
		vat.doArgs(new Integer(1),new Integer(2));

	}
	void doArgs(Integer i)
	{
		System.out.println("Integer i");
	}
	void doArgs(int i)
	{
		System.out.println("int i");
	}
	void doArgs(int... i)
	{
		System.out.println("int... i");
	}
	void doArgs(Integer... i)
	{
		System.out.println("Integer... i");
	}

}
   

If I compile this program , I am getting below compilation errors.
VarArgsTest.java:9: reference to doArgs is ambiguous, both method doArgs(int...) in VarArgsTest and method doArgs(java.lang.Integer...) in VarArgsTest match
vat.doArgs(1,2);
^
VarArgsTest.java:11: reference to doArgs is ambiguous, both method doArgs(int...) in VarArgsTest and method doArgs(java.lang.Integer...) in VarArgsTest match
vat.doArgs(new Integer(1),new Integer(2));
^
2 errors

If I do coment the any one of doArgs(int...) , doArgs(java.lang.Integer...) method , it is compiling and running fine. My doubt is that why is compiler treating doArgs(Integer i) and doArgs(int i) are different. In that case doArgs(int...) , doArgs(java.lang.Integer...) should be treated as different. Can you please explain.

[Ruben Soto]

Hi Santosh,

Try reading this thread. Look at the last few posts that contain some amendments that I think are relevant for your question. Let us know if you have further doubts.

[Morteza Manavi-Parast]

Or if you find those golden rules confusing or overkill, read the following:

The algorithm used by the compiler for the resolution of overloaded methods incorporates the following phases:

1. It first perform an overloaded resolution without using any boxing, unboxing, widening or varargs.
2. If the phase 1 fails then compiler tries to find a match by using boxing, unboxing or widening but exclude varargs.
3. If phase 2 failes too, then the compiler look at the varargs methods and tries to find a match for the method call combine boxing, unboxing and widening.

So you see, when the compiler looking at the varargs methods, it already passed phase 2 which means that now using box/unbox/widening or not using box/unbox/widening is the same for the compiler when it comes to varargs. So basically for the compiler boxing and then call a vararg method is the same as just using the vararg method and none of those has any precedence/preference to each other.

If you learn the above three steps, you never be confused by such those questions. Var-Args methods comes with a bunch of tricky points and this is one of them.

[San Daida]

You are right Morteza , Golden rules are not easy to understand and killing my mind.
What ever rules you mentioned are easy to capture and remember. Thanks for your reply