Can a class has two main's

[Narayana.Vaddi]

   
public class Test3 {
      public static void main(String[] args) {
            System.out.println("Main Method1");
      }
      public static void main(String args){
            System.out.println("Main Method2");
     }
}
 

If So then which one will be triggered?? I am pasting the piece of code for reference.

[Narayana.Vaddi]

  public class Test3 {
      public static void main(String[] args) {
            System.out.println("Main Method1");
      }
      public static void main(String []args){
            System.out.println("Main Method2");
     }
}
  

I didn't pasted the code correctly,this is the correct code!!

[camelia codarcea]

Hello,

well, you can have two methods "main" with the condition that the list of arguments is different for the two. This is the the principal rule for overloading a method (this is what you are trying to do). This applys not only to "main" method, but to any other method made in Java.
So, the code in your second post will not compile, because the list of parameter is the same (String[] args), but the code in the first post will compile.
At runtime the method "main" with (String[] args) will be automatically called.

[Narayana.Vaddi]

I tried running the code pasted first but according to you i have to get the output as Main Method1 and Main Method2, but i am getting the Main Method1 only, how come it can be,as it is not taking any arguments or is there any other reason

[camelia codarcea]

Hi,

I never said you should get both "Main Method1" and "Main Method2"!!!
What I said is that the first post is correct, it will compile, but only the first method will be automatically called, because it has the "String[] args" as the list of parameters.

The second method will not be called (it is not explicitly called from the first method), so you cant get also the result "Main Method2".

If you want to get also the "Mai Method2", you should change your code as following:

public static void main(String[] args) {
System.out.println("Main Method1");
main("somethig"); // this calls the overloaded method "main" !!!
}
public static void main(String args){
System.out.println("Main Method2");
}

[Ben Souther]

"Narayana",
Please check your private messages.

[marc weber]

A method's signature is its name combined with its argument list. So if you change the argument list, that's enough to change the signature.

A main method used as an entry point must be "public static void" with a String array as its only argument. You can overload main, but the overloaded versions can't be used as an entry point.

(Note: In this context, we're concerned only with the order and the types of the arguments. We don't care about the local variable names.)

[Arjun Reddy]

Hi,

I was just watching this thread and I have a question. Why doesn't the below code work where as the commented part works?/

class TwoMainMethods
{
public static void main(String[] args)
{
System.out.println("Method 1!");
main(2); //main("2");
}

public static void main(int[] args) // String args
{
System.out.println("Method 2!");
}

}

Thanks.

[ February 09, 2008: Message edited by: Arjun Reddy ]
[ February 09, 2008: Message edited by: Arjun Reddy ]

[Vikram Shinde]

main(2); //main("2");
}

public static void main(int[] args) // String args
{

[Vikram Shinde]

main(2); //main("2");
}

public static void main(int[] args) // String args
{


It should have main method with int as parameter not int[] array
try this-public static void main(int args)

[marc weber]

Originally posted by Arjun Reddy:
...where as the commented part works? ...

I'm not sure I understand your question, because the commented part does not work.

You have a main method defined to take a String array, and another main method defined to take an int array. You're trying to call main using an int (2) or a String ("2"). Neither of these calls will work, because neither are using arrays.

On the other hand, if you define your main methods to take varargs, then these calls would work, because the int and String would be automatically put into arrays of size 1.

(Warning: If you use varargs with main(String... args) and call main("2") inside that method, then you will have infinite recursive calls.)

[Ali Khalfan]

come to think of it: var-agrs won't work either

 
 public static void main(String [] args){
    System.out.println("original");
    }
    
    public static void main(String... x){
    System.out.println("tst");
    }    

A var arg and an array is the same isn't it? they can't be overloaded anyway...interesting

[Thiago Furuchima]

Hi everyone.

Please always note that the "public static void main(String[] args){...}" method is, for understanding proposals, like any other public static method. So tou canot use the same signature to declare two methods in the same class.

tks.

[marc weber]

Originally posted by Ali Khalfan:
... A var arg and an array is the same isn't it? they can't be overloaded anyway...

That's correct. Varargs just puts the array instantiation behind the scenes.

What I meant by suggesting varargs is replacing the array argument with a vararg...

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

This way, you could call main with a single String -- for example, main("2"); -- and the String would be "packaged" into a String array containing a single element.
[ February 10, 2008: Message edited by: marc weber ]

[Jart Bo]

Hi Marc,

In short, these two below are the same method declarations. Is that correct?

public static void main( String args[] )
{
//
}

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

But Java 5.0 suggests that the 1st one should be the standard signature, right?

[marc weber]

This Java Tech Tips article talks about similarities and differences between varargs and arrays.

[camelia codarcea]

Hello Ali,

you wrote:
come to think of it: var-agrs won't work either
code:
public static void main(String [] args){
System.out.println("original");
}

public static void main(String... x){
System.out.println("tst");
}


But, actualy, both work, becaue starting with java 1.5, there are accepted the following three signatures for the main method (page 766 K-B book)

static public void main(String[] args)
public static void main(String... x)
static public void main(String bang_a_gong[])

So, the important things are: the method should be static and public, should be called "main". The parameter can be either var-args, or an array of Strings.

[marc weber]

Originally posted by camelia codarcea:
...actualy, both work...

I think Ali's point is that these will not work together. In other words, either one works by itself, but this is not a valid way to overload a method.

The reason is that varargs is just a shorthand way of using an array as a parameter. So the three examples you gave are not really different signatures -- they are just different ways of writing it.