Program to convert binary to decimal number?

Question

I only know how to do a program that converts only 4 numbers, but it to convert any amount of digits the number enters, I think you need to use a loop or something, but I'm not sure how. Could someone please help me? This is my code so far:
import javax.swing.JOptionPane;
public class bintodec {
     public static void main (String[] args) {
          String input;
          int number,digit1,digit2,digit3,digit4,result;
          input = JOptionPane.showInputDialog ("Enter a binary number.");
          number = Integer.parseInt(input);
          digit1 = ((number % 10000) - (number % 10000 % 1000)) / 1000;
          digit2 = ((number % 1000) - (number % 1000 % 100)) / 100;
          digit3 = ((number % 100) - (number % 100 % 10)) / 10;
          digit4 = (number % 10);
          result = (digit1 * 8) + (digit2 * 4) + (digit3 * 2) + (digit4 * 1);
          System.out.println ( "Binary number: " + input + "\nConverted Decimal Number: " + result);
          System.exit( 0 );
     } // main
} // bintodecany help is super-appreciated.

Answer 1

I am not sure if this will help you. Check it out, run it and let me know if it helped.
import java.util.*;
   public class BitwiseTest1 {
       public static void main(String[] args){
        System.out.println("Enter a integer number:");
        Scanner keyboard = new Scanner(System.in);
        int n1 = keyboard.nextInt();
        System.out.println( "n1 as binary " +
               Integer.toBinaryString( n1 ));
        System.out.println( "NOT n1 =     " +
               Integer.toBinaryString( ~n1 ));
        System.out.println("Enter another integer number:");
        int n2 = keyboard.nextInt();
        System.out.println( "n2 as binary " +
               Integer.toBinaryString( n2 ));
         System.out.println( "NOT n2 =     " +
               Integer.toBinaryString( ~n2 ));
}