Check out example codes for "a recursive function that calculates the greatest common divisor from user's input in java". It will help you in understanding the concepts better.

Code Example 1

```
/**
* Java program to demonstrate How to find Greatest Common Divisor or GCD of
* two numbers using Euclid’s method. There are other methods as well to
* find GCD of two number in Java but this example of finding GCD of two number
* is most simple.
*
* @author Javin Paul
*/
public class GCDExample {
public static void main(String args[]){
//Enter two number whose GCD needs to be calculated.
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter first number to find GCD");
int number1 = scanner.nextInt();
System.out.println("Please enter second number to find GCD");
int number2 = scanner.nextInt();
System.out.println("GCD of two numbers " + number1 +" and "
+ number2 +" is :" + findGCD(number1,number2));
}
/*
* Java method to find GCD of two number using Euclid's method
* @return GDC of two numbers in Java
*/
private static int findGCD(int number1, int number2) {
//base case
if(number2 == 0){
return number1;
}
return findGCD(number2, number1%number2);
}
}
Output:
Please enter first number to find GCD
54
Please enter second number to find GCD
24
GCD of two numbers 54 and 24 is :6
```

Code Example 2

```
/*
import scanner and instantiate scanner class;
declare your method with two parameters
declare a third variable;
set condition;
swap the parameter values if condition is met;
set second conditon based on result of first condition;
divide and assign remainder to the third variable;
swap the result;
in the main method, allow for user input;
Call the method;
*/
public class gcf {
public static void main (String[]args){//start of main method
Scanner input = new Scanner (System.in);//allow for user input
System.out.println("Please enter the first integer: ");//prompt
int a = input.nextInt();//initial user input
System.out.println("Please enter a second interger: ");//prompt
int b = input.nextInt();//second user input
Divide(a,b);//call method
}
public static void Divide(int a, int b) {//start of your method
int temp;
// making a greater than b
if (b > a) {
temp = a;
a = b;
b = temp;
}
while (b !=0) {
// gcd of b and a%b
temp = a%b;
// always make a greater than b
a =b;
b =temp;
}
System.out.println(a);//print to console
}
}
```

Code Example 3

```
public int gcd(int a, int b) {
if (b==0) return a;
return gcd(b,a%b);
}
```

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