How to generate OTP Number with 6 digits

Question

What is an OTP number in a login authentication system? Is there any specific algorithm for generating OTP numbers using java (android). Or is an OTP something like random number? How can this be achieved, with optimization.

Answer 1

Easiest way is to just use DecimalFormat with Random class.

String otp= new DecimalFormat("000000").format(new Random().nextInt(999999));
System.out.println(otp);

Sample Outputs,

002428
445307
409185
989828
794486
213934

Answer 2

public static void main(String []args){
            java.util.Random r=new java.util.Random();
            int otp = r.nextInt(1000000); // no. of zeros depends on the OTP digit
            System.out.println(otp);
}