convert decimal to binary in java

import java.util.Scanner;
public class BinaryToDecimalDemo 
{
   public static void main(String[] args) 
   {
      int number, decimal = 0, a = 0;
      Scanner sc = new Scanner(System.in);
      System.out.println("Please enter binary number: ");
      String strBinary = sc.nextLine();
      number = Integer.parseInt(strBinary);
      while(number != 0){
         decimal += (number % 10) * Math.pow(2, a);
         number = number / 10;
         a++;
      }
      System.out.println("Decimal number: " + decimal);
      sc.close();
   }
}

public class DecimalToBinaryExample2{    
public static void toBinary(int decimal){    
     int binary[] = new int[40];    
     int index = 0;    
     while(decimal > 0){    
       binary[index++] = decimal%2;    
       decimal = decimal/2;    
     }    
     for(int i = index-1;i >= 0;i--){    
       System.out.print(binary[i]);    
     }    
System.out.println();//new line  
}    
public static void main(String args[]){      
System.out.println("Decimal of 10 is: ");  
toBinary(10);    
System.out.println("Decimal of 21 is: ");  
toBinary(21);    
System.out.println("Decimal of 31 is: ");    
toBinary(31);  
}}    

Convert decimal to binary using toBinaryString() method
public class DecimalToBinary
{
   public static void main(String[] args)
   {
      System.out.println("decimal to binary using toBinaryString() 104: ");
      // to binary string java
      System.out.println(Integer.toBinaryString(104));
      System.out.println("\ndecimal to binary using toBinaryString() 554: ");
      // tobinarystring
      System.out.println(Integer.toBinaryString(554));
      System.out.println("\ndecimal to binary using toBinaryString() 644: ");
      System.out.println(Integer.toBinaryString(644));
   }
}