convert decimal number to binary in java without using array

1public class DecimalToBinaryWithoutArray
2{
3   static void toBinary(int num)
4   { 
5      StringBuilder sb = new StringBuilder(); 
6      int a = 0;
7      while(num > 0)
8      {
9         sb.append(num % 2);
10         a++;
11         num = num / 2;
12      }
13      System.out.println(sb.reverse()); 
14   }
15   public static void main(String[] args) 
16   {
17      int number = 20; 
18      toBinary(number);
19   }
20}

1public class DecimalToBinaryExample2{    
2public static void toBinary(int decimal){    
3     int binary[] = new int[40];    
4     int index = 0;    
5     while(decimal > 0){    
6       binary[index++] = decimal%2;    
7       decimal = decimal/2;    
8     }    
9     for(int i = index-1;i >= 0;i--){    
10       System.out.print(binary[i]);    
11     }    
12System.out.println();//new line  
13}    
14public static void main(String args[]){      
15System.out.println("Decimal of 10 is: ");  
16toBinary(10);    
17System.out.println("Decimal of 21 is: ");  
18toBinary(21);    
19System.out.println("Decimal of 31 is: ");    
20toBinary(31);  
21}}