// Project: Observer
// Module: messageboard2 Example
// Source code file: Main.java
// Illustrate the Observer software pattern.
// In addition to the currentMessage, an
// archive of old messages is kept in
// an array list.

public class Main {

    public static void main(String[] args)
            throws InterruptedException {

        // Test the Observer and Observable classes.
        MessageBoard board = new MessageBoard( );
        Student bob = new Student("Bob");
        Student alice = new Student("Alice");
        board.addObserver(bob);
        board.addObserver(alice);
        System.out.println("Number of observers: " +
                board.countObservers( ));
        System.out.println( );

        board.changeMessage("Homework 5 Description posted");
        // Sleep (pause) for 1000 milliseconds (1 second).
        Thread.sleep(1000);
        board.changeMessage("Final Exam Review posted");
        Thread.sleep(1000);
        board.changeMessage("Grades for Homework 5 posted");
        Thread.sleep(1000);

        // Anyone allowed to check the message archive even
        // if he or she has not been recently been notified.
        // board.hasChanged will be true if the messages are in
        // the process of being changed before the observers are
        // notified.  If board.hasChanged is false, a student is
        // guaranteed to obtain the most recently posted messages.
        if (!board.hasChanged( )) {
            System.out.println("Message Archive");
            System.out.println("====================");
            System.out.println(board.getArchive( ));
        }
    }
}