Difference between revisions of "Var-Args"

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</syntaxhighlight>
 
</syntaxhighlight>
  
* Where it differs from an array is that For a var-args method, the method parameter can be passed "normally", instead of being passed as an array
+
* Where it differs from an array is that For a var-args method, the method parameter can also be passed "normally", in addition to being passed as an array.
 
* Example:
 
* Example:
  
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public static void main(String[] args) {
 
public static void main(String[] args) {
             System.out.println(vasum(2, 3, 4));               //Varargs invocation
+
             System.out.println(vasum(2, 3, 4));               //Variable arguments invocation
    System.out.println(arrsum(new int[] {2, 3, 4}));  //Array 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
 
}
 
}
 
 

Revision as of 22:45, 25 August 2011

  • 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 argument is treated as an array within the method. so nums is an int[] array.
  • Example main() can be legally rewritten as :
public static void main(String... args) {

}
  • Where it differs from an array is that For a var-args method, the method parameter can also be passed "normally", in addition to being passed as an array.
  • 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
}