I need a refresher on moving classes from one file into two files. My sample code is in one file called "external_class_file_main". The program runs fine and the code is shown below:

Public class external_class_file_main {

    public static int get_a_random_number (int min, int max) {
        int n;
        n = (int)(Math.random() * (max - min +1)) + min;
        return (n);

    }

    public static void main(String[] args) {
        int r;
        System.out.println("Program starting...");

        r = get_a_random_number (1, 5);
        System.out.println("random number = " + r);

        System.out.println("Program ending...");

    }

}

I move the get_a_random_number class to a separate file called "external_class_file". When I do this, I get the following error:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
The method get_a_random_number(int, int) is undefined for the type
external_class_file_main
at external_class_file_main.main(external_class_file_main.java:20)

The "external_class_file_main" now contains:

public class external_class_file_main {

    public static void main(String[] args) {
        int r;
        System.out.println("Program starting...");

        r = get_a_random_number (1, 5);
        System.out.println("random number = " + r);

        System.out.println("Program ending...");

    }

}

The "external_class_file" now contains:

public class external_class_file {

    public static int get_a_random_number (int min, int max) {
        int n;
        n = (int)(Math.random() * (max - min +1)) + min;
        return (n);

    }

}