main method String

[chandrasekhar.melam]

class sample
{
public static void main()
{
System.out.println("Hai");
}
}
if we compile the above program it doesnot shows any error msgs.. But you run the above program it shows an error msg as java.lang.NoSuchClassFound...... why?

[sehudson]

you are missing the argument in your main

public class Sample {

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

make that change, recompile and try it again.

[chandrasekhar.melam]

Sir, Idont want create a pakage.... Iam asking why the java interpreter sends an error msg while running the above program....

[sehudson]

ignore the package name. just add the String[] args inside the main parenthesis.

[chandrasekhar.melam]

Sir, that's iam saying,
If we write string args[] in main it gives the o/p. but if we dont write the program complied successfully.. But while running that program it shows an error msg. why?

[Rameshwar Soni]

Java interpreter sends the message because it is looking for the method with the signature public static void main(String[] a)
and you have not written that. Secondly, you are telling that you are getting the error java.lang.NoSuchClass error which i think you should not get and you
will get java.lang.NoSuchMethodError

[chandrasekhar.melam]

Thank you Rameshwar.
It means it's essential thing to write string args[] in main... without writing this we cannot run this right?
But in c/cpp we dont declare any variable..... why it's essential to write in java?

[chandrasekhar.melam]

if i dont want to parse the values to main, so in this case it's not essential to write string args[] in main right?

[Norm]

The java program only looks for a main(String[] ) method as the starting point to the program.
Ask the author of the java program why he only wanted that one entry point.
Its not important enough to argue about. It works. use it.

[chandrasekhar.melam]

try this:
class sample
{
static
{
sample.main();
System.exit(0);
}
public static void main()
{
System.out.println("Hai");
}
}
In the above program the main method dint recive any values. and you run this above progrm you get the o/p. why?

[Rameshwar Soni]

This is what the Java creators had decided. It should be there means it should be there and we have to follow certain rules.
Why 2+2=4 and not 5. I don't know but it is said 4 and it is 4. Anyways

why it's essential to write in java?

See it is essential in Java because what would you do if you want to pass certain arguments at run-time? So what ever you pass at run-time is stored in String array
which you declare in main method. I think an example is best to explain

class Demo
{ 
   public static void main(String[] args)
   {
        int ans=(Integer.parseInt(args[0])) +(Integer.parseInt(args[2]));
	System.out.println(ans)	;
    }
}

you will run this program java Demo 2 3 and the output is 5.
So you can see how that array in main method was used.

[chandrasekhar.melam]

ya i know this one. if i dont send the command line arguments, then?

[Norm]

In your code sample you could have called the method anything. It didn't have to be main.

class Sample {
  static {
     Sample.startHere();
     System.exit(0);
  }

  public static void startHere() {
    System.out.println("Hai");
  }
}

[chandrasekhar.melam]

ya i know. bcz the static is block which was called before the main method called, right.

[Norm]

The main method in your code would not be called by the java program. It's Your code that calls it and it could be with any name as far as java is concerned.

[chandrasekhar.melam]

is main method is predefined or userdefined method?

[Norm]

Please explain what is predefined and what is userdefined.

[chandrasekhar.melam]

both(pre and user defined datatype).
Bcz the main method was created by user. that's way we called it as user defined. and
every java program excution was starts with main method. it's predefined. so that's way we called predfined. Right?

[Norm]

the main method was created by user. that's way we called it as user defined.

That is correct. I type in/create all of the code in my programs.

every java program excution ... starts execution with main method. it's predefined.

That is correct. The java program calls a public static main(String[]) method.

[chandrasekhar.melam]

thank for giving some nice answers. but the confusion was stilll going. ok