Var-Args

• Var-args are used to defined methods with variable argument lists.
• Syntax <type>... <varargname>
• Example:

public class VarArgs {

	public static void main(String[] args) {
		System.out.println(sum(2, 3, 4));
	}
	
	public static int sum(int... nums) {
		int sum = 0;
		for(int i : nums) {
			sum += i;
		}
		return sum;
	}

}

• The ellipsis can be located anywhere e.g. (int... nums) or (int ...nums) or (int ... nums) is fine.
• Essentially the method arguments are implicitly converted into an array and passed to the method. so nums is an int[] array.
• Example main() can be legally rewritten as :

public static void main(String... args) {

}

• For a var-args method, the method parameters can also be passed as an array argument. In this case, it will be treated as a non var-args call, since the argument and the parameter both match.
• Example:

public class VarArgs {

	public static void main(String[] args) {
            System.out.println(vasum(2, 3, 4));	              //Variable arguments invocation
            System.out.println(vasum(new int[] {1, 2, 3});    //Array invocation also OK for var-args
	    System.out.println(arrsum(new int[] {2, 3, 4}));  //Only Array invocation is possible
	}
	
	public static int vasum(int ... nums) {
		int sum = 0;
		for(int i : nums) {
			sum += i;
		}
		return sum;
	}
	
	public static int arrsum(int[] nums) {
		int sum = 0;
		for(int i : nums) {
			sum += i;
		}
		return sum;
	}

}

• The var-args must be the last parameter in the method's signature. Why ? To resolve situations like this :

sum2(2, 3); 

public static void sum2(int a, int... nums) {
}

• Only one var-arg can be declared in the method (even if the var-args are of different types)

public static void sum3( String... strs, int... nums) { //ILLEGAL
}

Var-Args Overloading

• Because arguments to var-arg methods are implicitly passed as arrays, the following will NOT compile, both the foo()'s have the same signature:

private static void foo(int...ia2) {
		
}
	
private static void foo(int[] ia2) {
		
}