Write a program that performs the following tasks: Display a friendly greeting to the user Prompt the user for the value to convert (a String) Accept that String Prompt the user for the value of the initial base (an integer) Accept that integer Prompt the user for the desired base of the output (an integer) Accept that integer If the String is not a legal expression of a number in the initial base, display an error message and exit the program. Convert the value represented by the String in the initial base to the desired base. Display the result.

Explanation:

import java.util.Scanner;

import java.math.BigInteger;

public class Main

{

private int x;  

public static boolean isValidInteger(String theValue, int theBase)

{    

BigInteger number = new BigInteger(theValue,theBase);

if(theValue.equals(number.toString(theBase)))

{

return true;

}

else

return false;

}

public static String convertInteger(String theValue, int initialBase, int finalBase)

{

boolean valid=isValidInteger(theValue,initialBase);

if(valid==true)

{

BigInteger number = new BigInteger(theValue);

return(number.toString(finalBase));

}

else

return("String not in initial base");  

}

public static void main(String[] args)

{

System.out.println("Welcome");

String value;

int ibase, dbase;

if(args.length==0)

{

Scanner S = new Scanner(System.in);

System.out.println("Enter Value to be converted :: ");

value = S.nextLine();

System.out.println("Enter initial base :: ");

ibase = S.nextInt();

System.out.println("Enter desired base :: ");

dbase = S.nextInt();

}

else

{

value=args[0];

ibase=Integer.parseInt(args[1]);

dbase=Integer.parseInt(args[2]);

}

  System.out.println("Change base "+convertInteger(value,ibase,dbase));  

}

}

Output

(because i need 20 chars)