Chapter 18 Exercise 3, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

18.3 (Compute greatest common divisor using recursion)

Write a recursive method to find the GCD. Write a test
program that prompts the user to enter two integers and
displays their GCD.

import java.util.Scanner;

public class Exercise_03 {

    public static void main(String[] args) {
        System.out.println("Enter two integers: ");
        Scanner input = new Scanner(System.in);
        int n1 = input.nextInt();
        int n2 = input.nextInt();

        System.out.println("The GCD is " + gcd(n1,n2));

    }

    private static int gcd(int n1, int n2) {
        if (n1 % n2 == 0)
            return n2;
        else
            return gcd(n2, n1 % n2);
    }

}