Sample

import java.io.*;

public class factorial {
    public static int fac(int a){
          int num = a;                 
          int result = 1;
          while(num>0){
                result = result * num;
                num--;
          }
          return result;
    }
    public static void main (String args[]){
        InputStreamReader istream = new InputStreamReader(System.in);
        BufferedReader bufRead = new BufferedReader(istream) ;
        int num=0;
        System.out.print("Enter Number: ");
        try{
            num=Integer.parseInt( bufRead.readLine() );
            System.out.println("Factorial of "+num+"is:"+fac( num));
        }catch( Exception Number ){
            System.out.println("Invalid Number!");
        }
    }
}