Method 1

//Java program to convert octal number to binary number
class Main
{
    public static void main(String args[])
    {
        int octal = 12;

        //Declaring variable to store decimal number
        int decimal = 0;
        //Declaring variable to use in power
        int n = 0;

        //writing logic for the octal to decimal conversion
        while(octal > 0)
        {
            int temp = octal % 10;
            decimal += temp * Math.pow(8, n);
            octal = octal/10;
            n++;
        }

        int binary[] = new int[20];
        int i = 0;

        //writing logic for the decimal to binary conversion
        while(decimal > 0)
        {
            int r = decimal % 2;
            binary[i++] = r;
            decimal = decimal/2;
        }

        //printing result
        System.out.print("Binary number : ");

        for(int j = i-1 ; j >= 0 ; j--)
            System.out.print(binary[j]+"");

    }
}