Converting Decimal Integer into Binary Number

import java.io.*;
import java.util.*;
public class Binary
{
    public static void main(String [] args)
    {
        Scanner input = new Scanner(System.in);
        System.out.println(" Enter Number ");
        int num = input.nextInt();
        int temp = num;
        String b=null;
        while(temp>0)
        {
            int a;
            a=temp%2;
            temp=temp/2;
            if(b==null)
            {
            b=String.valueOf(a);
            }
            else
            {
                b=String.valueOf(a)+b;
            }
        }
        System.out.println("Number in binary representation");
        System.out.println(b);
    }
}