public class BinaryOctal {

    public static void main(String[] args) {
        long binary = 101001;
        int octal = convertBinarytoOctal(binary);
        System.out.printf("%d in binary = %d in octal", binary, octal);
    }

    public static int convertBinarytoOctal(long binaryNumber)
    {
        int octalNumber = 0, decimalNumber = 0, i = 0;

        while(binaryNumber != 0)
        {
            decimalNumber += (binaryNumber % 10) * Math.pow(2, i);
            ++i;
            binaryNumber /= 10;
        }

        i = 1;

        while (decimalNumber != 0)
        {
            octalNumber += (decimalNumber % 8) * i;
            decimalNumber /= 8;
            i *= 10;
        }

        return octalNumber;
    }
}

101001 in binary = 51 in octal

Binary To Decimal
1 * 25 + 0 * 24 + 1 * 23 + 0 * 22 + 0 * 21 + 1 * 20 = 41

Decimal to Octal
8 | 41
8 | 5 -- 1
8 | 0 -- 5
(51)

public class OctalBinary {

    public static void main(String[] args) {
        int octal = 67;
        long binary = convertOctalToBinary(octal);
        System.out.printf("%d in octal = %d in binary", octal, binary);
    }

    public static long convertOctalToBinary(int octalNumber)
    {
        int decimalNumber = 0, i = 0;
        long binaryNumber = 0;

        while(octalNumber != 0)
        {
            decimalNumber += (octalNumber % 10) * Math.pow(8, i);
            ++i;
            octalNumber/=10;
        }

        i = 1;

        while (decimalNumber != 0)
        {
            binaryNumber += (decimalNumber % 2) * i;
            decimalNumber /= 2;
            i *= 10;
        }

        return binaryNumber;
    }
}

67 in octal = 110111 in binary

Octal To Decimal
6 * 81 + 7 * 80 = 55

Decimal to Binary
2 | 55
2 | 27 -- 1
2 | 13 -- 1
2 | 6  -- 1
2 | 3  -- 0
2 | 1  -- 1
2 | 0  -- 1
(110111)