Java - var-arg 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 var-arg method

1. Below them let's check which is correct use of 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

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