why we cant use interger or float at the place of string in main

Question

public static void main(string []Arg)

Answer 1

it is a rule of java. so that JVM can start the program. If you need number as input, you can cast from string.
e.g.
int i = Integer.parseInt(args[0]);

Answer 2

we can
then other will be:

public class numbers
{
public static void main (int a, int b)
{
//int a=0;
//int b=0;
int sum=a+b;
System.out.println ("the sum of two numbers is="+sum");
}
}