Example 1: Program to convert binary number to decimal

public class BinaryDecimal{

    public static void main(String[] args){
        long num = 110110111;
        int decimal = convertBinaryToDecimal(num);
        System.out.printf("%d in binary = %d in decimal", num, decimal);
    }

    public static int convertBinaryToDecimal(long num){
        int decimalNumber = 0, i = 0;
        long remainder;
        while (num != 0)
        {
            remainder = num % 10;
            num /= 10;
            decimalNumber += remainder * Math.pow(2, i);
            ++i;
        }
        return decimalNumber;
    }
}

Output

110110111 in binary = 439 in decimal

Example 2: Program to convert decimal number to binary

public class DecimalBinary{

    public static void main(String[] args){
        int num = 19;
        long binary = convertDecimalToBinary(num);
        System.out.printf("%d in decimal = %d in binary", num, binary);
    }

    public static long convertDecimalToBinary(int n){
        long binaryNumber = 0;
        int remainder, i = 1, step = 1;

        while (n!=0)
        {
            remainder = n % 2;
            System.out.printf("Step %d: %d/2, Remainder = %d, Quotient = %dn", step++, n, remainder, n/2);
            n /= 2;
            binaryNumber += remainder * i;
            i *= 10;
        }
        return binaryNumber;
    }
}

Output

Step 1: 19/2, Remainder = 1, Quotient = 9
Step 2: 9/2, Remainder = 1, Quotient = 4
Step 3: 4/2, Remainder = 0, Quotient = 2
Step 4: 2/2, Remainder = 0, Quotient = 1
Step 5: 1/2, Remainder = 1, Quotient = 0
19 in decimal = 10011 in binary