wap to calculate factorial

/*wap to calculate factorial*/

import java.lang.*;
class factorial
{
 int num;
 factorial(int a)
    {
     num=a;
    }
 int fact(int m)
   {
    if(m==0)
    return(1);
    else
    return(m*fact(m-1));
   }
 void display()
    {
     int f;
     f=fact(num);
     System.out.println("factorial is="+f);
    }
}
class demo_factorial
{
 public static void main(String arg[])
   {
    factorial f1=new factorial(3);
    f1.display();
   }
}