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 class ChatUser extends Thread {
    private String userName;
    private boolean running = true;
    private boolean paused = false;

    public ChatUser(String name) {
    	this.userName = name;
    }

    // Pause the thread
    public void pauseUser() {
        paused = true;
    }

    // Resume the thread
    public synchronized void resumeUser() {
        paused = false;
        notify(); // wake up thread if it is waiting
    }

    // Stop the thread
    public void stopUser() {
        running = false;
        resumeUser(); // in case it's paused
    }

    public void run() {
    	int count = 1;
        try {
            while (running) {
                synchronized (this) {
                    while (paused) {
                    	wait(); // wait if paused
                    }
                }
                System.out.println(userName + " sent message " + count);
                count++;
                Thread.sleep(500);
            }
        } catch (InterruptedException e) {
        	System.out.println(userName + " interrupted.");
        }
        System.out.println(userName + " stopped.");
    }
}

public class SimpleChatSimulation {
    public static void main(String[] args) throws Exception {
    	ChatUser u1 = new ChatUser("Alice");
        ChatUser u2 = new ChatUser("Bob");

        // Set priorities
        u1.setPriority(Thread.NORM_PRIORITY); // normal priority
        u2.setPriority(Thread.MAX_PRIORITY);  // higher priority

        // Start threads
        u1.start();
        u2.start();
        System.out.println("Alice alive? " + u1.isAlive());
        System.out.println("Bob alive? " + u2.isAlive());

        // Let them run for 2 seconds 
        Thread.sleep(2000);

        // Pause Bob
        System.out.println("Pausing Bob...");
        u2.pauseUser();
        Thread.sleep(2000);

        // Resume Bob
        System.out.println("Resuming Bob...");
        u2.resumeUser();
        Thread.sleep(2000);

        // Stop both
        System.out.println("Stopping both users...");
        u1.stopUser();
        u2.stopUser();

        // Join to wait for them to finish
        u1.join();
        u2.join();

        System.out.println("Alice alive? " + u1.isAlive());
        System.out.println("Bob alive? " + u2.isAlive());
        System.out.println("Simulation finished.");
    }
}