Java - varargs Method / Chapter - 6 /Language Fundamental (1.5v)

var-arg method    (variable number of argument method )

1. Until 1.4 we can't declare a method with the variable number of arguments.If there is a change in the number of arguments compulsory we should go for the new method.But this increases the length of the code & readability.


2. To overcome this problem java makers introduced the var-args method in 1.5 version of JDK(java).According to this, we can declare a method which can take the variable number of arguments, such type of method are called var-arg methods.


3. we can declare a var-arg method as follows:-

Syntax:
m1(int...   x)
where m1 is a method name & int .... x as an arguments type (we can take any type)

4.we can call this method by passing any number of arguments of int values including 0 number also.

example 1:-
m1( );
m1(10);
m1(10,20 );
m1(10,20,30,40, );

example 2:-

class Test
{
public static void m1()
{
System.out.println("var-arg method called");
}
public static void main(System.out.println);
{
m1();
m1(10);
m1(10,20);
m1(10,20,30,40);
}
}

        o/p of the above program is as follows;-

var-arg method called
           var-arg method called

var-arg method called
           var-arg method called

critical point while using the var-arg method

1. Below them let's check which is the correct use of the var- arg method.

    example:

• m1(int ...       x)                (valid)


• m1(int       ...x )                (valid)


• m1(int...x )                       (valid)


• m1(int      x... )                (invalid)


• m1(int.      ..x )                (invalid)


• m1(int      .x.. )                (invalid)    

we should not separate the dots .

2. We can use mix var-arg parameter with normal arguments.

      example:-

      m1(int x,int...   y)                     (valid)

      m1(String s,double...  y)          (valid)

 3.If we are using normal parameters with var-arg parameter the var-arg parameter should be the last parameter.

        example:-

               m1(String ....s ,double d)             (invalid)

              m1(double d, String...   s)              (valid)

4. Inside the var-arg method, we can take only one var-arg parameter and we can't take more than one var-arg parameter.

       example:-

               m1(String ....s ,double d)             (invalid)

5.If there is a collision between var-arg method & general method then general method always wins.

   example:-

      class Test

     {

            public static void m1(int...   x)

           {

                 System.out.println("var-arg method called");

            }

           public  static void m1(int x)

          {

                System.out.println("general  method called");

          }

         public static void main(String [ ] args )

          {

                    m1();

                   m1(10,20);

                  m1(10,20,30,40);

                  m1(10);

            }

    }

The output of the following program is:-

var-arg method called

var-arg method called

var-arg method called

general method called