Here is a java example that converts octal to binary.

import java.io.*;
class ConvertOctalToBinary{
    public static void main(String[] args)throws Exception{
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Enter octal number: ");
        String oct = br.readLine();
        int i= Integer.parseInt(oct,8);
        String binary=Integer.toBinaryString(i);
        System.out.println(binary);
    }
}