java - Using int Instead Of String: public static void main (int[] args)

Question

I was under the impression that the main method had to have the form "public static void main (String[] args){}", that you couldn't pass int[] arguments.

However, in windows commandline, when running the following .class file, it accepted both int and string as arguments.

For example, using this command will give the output "stringers": "java IntArgsTest stringers"

My question is, why? Why would this code accept a string as an argument without an error?

Here is my code.

public class IntArgsTest 
{
    public static void main (int[] args)
    {

        IntArgsTest iat = new IntArgsTest(args);

    }

    public IntArgsTest(int[] n){ System.out.println(n[0]);};

}

Answer 1

Everything passed into main method, the one used by the JVM to start a program, is a String, everything. It may look like the int 1, but it's really the String "1", and that's a big difference.

Now with your code, what happens if you try to run it? Sure it will compile just fine since it is valid Java, but your main method signature doesn't match the one required by the JVM as the starting point of a program.

For your code to run, you'd need to add a valid main method like,

public class IntArgsTest {
   public static void main(int[] args) {

      IntArgsTest iat = new IntArgsTest(args);

   }

   public IntArgsTest(int[] n) {
      System.out.println(n[0]);
   };

   public static void main(String[] args) {
      int[] intArgs = new int[args.length];

      for (int i : intArgs) {
         try {
            intArgs[i] = Integer.parseInt(args[i]);
         } catch (NumberFormatException e) {
            System.err.println("Failed trying to parse a non-numeric argument, " + args[i]);
         }
      }
      main(intArgs);
   }
}

And then pass some numbers in when the program is called.