// COM1204 - FILE WITH THREE JAVA SOURCE FILES
// FOR A VERY SIMPLE NETWORK SIMULATION.

/*
 * Simplest demo network simulation.  
 * class Sim.java R P Futrelle,
 * 7/18/2001 
 */

/**
 * Creates the initial objects and runs
 * the simulation loop.
 * Rather than doing this all in static functions,
 * a single instance of Sim is created and used.
 */

public class Sim {

    Link link;
    Node[] nodes;

    public static void main(String[] args){
    
	Sim sim = new Sim();
	sim.run();

    } // main()

    private Sim() {
	
	link = new Link();
	nodes = new Node[2];
	for(int i=0; i < 2; i++)
	    nodes[i] = new Node(i,link);

    }// Sim()

    /**
     * Loops by running nodes
     */
    private void run() {

	for(int j = 0; j < 5; j++) {
	    nodes[0].send();
	    nodes[1].send();
	    System.out.println("0 " +  nodes[0].receive());
	    System.out.println("1 " +  nodes[1].receive());
	    link.clear();
	}

    } // run()

}// class Sim

// ********************************************************

/*
 * Simplest demo network simulation.
 * class Link.java
 * R P Futrelle, 7/18/2001
 */

/**
 * Simple passive link. 
 * Holds one message.
 */

public class Link {

    Object msg;

    public static void main(String[] args){

    } // main()


   public Link() {
	
	msg = null;

    }// Node()

    public void insert(Object m) {

	msg = m;

    } // insert()

    public Object retrieve () {

	return msg;

    } // retrieve()


    public void clear() {

	msg = null;

    } // clear()


}// class Link

// ********************************************************

/*
 * Simplest demo network simulation.
 * class Node.java
 * R P Futrelle, 7/18/2001
 */

/**
 * A node might be a workstation or PC on the net.
 * It is attached to the link and sends and receives
 * messages
 */

public class Node {

    Link link;
    int nodeID;

    public static void main(String[] args){

    } // main()

   public Node(int nodeID, Link ln) {
	
       link = ln;
       this.nodeID = nodeID;

    }// Node()

    public void send() {

	if(Math.random() < 0.1)
	    link.insert("Is there life on this net?");

    } // send()

    public Object receive() {

	return link.retrieve();

    } // receive

}// class Node