convert decimal to binary in java

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}

1int n = 1000;
2String s = Integer.toBinaryString(n);

1String binary = Integer.toBinaryString(num);

1public static String makeBinaryString(int n) {
2	StringBuilder sb = new StringBuilder();
3	while (n > 0) {
4    sb.append(n % 2);
5		n /= 2;
6	}
7  	sb.reverse();  	
8  	return sb.toString();
9}

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}}    

1Convert decimal to binary using toBinaryString() method
2public class DecimalToBinary
3{
4   public static void main(String[] args)
5   {
6      System.out.println("decimal to binary using toBinaryString() 104: ");
7      // to binary string java
8      System.out.println(Integer.toBinaryString(104));
9      System.out.println("\ndecimal to binary using toBinaryString() 554: ");
10      // tobinarystring
11      System.out.println(Integer.toBinaryString(554));
12      System.out.println("\ndecimal to binary using toBinaryString() 644: ");
13      System.out.println(Integer.toBinaryString(644));
14   }
15}