import java.util.Random;import java.util.Vector;import java.util.Enumeration;public class NetworkSimulator{        // This is the number of entities in the simulator    public static final int NUMENTITIES = 4;    // These constants are possible events    public static final int FROMLAYER2 = 0;    public static final int LINKCHANGE = 1;         // Parameters of the simulation    private boolean linkChanges;    private static int traceLevel;    private static EventList eventList;    private static Random rand;        // Data used for the simulation    private Entity[] entity;    public static int[][] cost;    private static double time;    // Initializes the simulator    public NetworkSimulator(boolean hasLinkChange, int trace, long seed)    {        linkChanges = false; //hasLinkChange; //set to FALSE        traceLevel = trace;        eventList = new EventListImpl();        rand = new Random(seed);        time = 0.0;                cost = new int[NUMENTITIES][NUMENTITIES];        cost[0][0] = 0;        cost[0][1] = 1;        cost[0][2] = 3;        cost[0][3] = 7;        cost[1][0] = 1;        cost[1][1] = 0;        cost[1][2] = 1;        cost[1][3] = 999;        cost[2][0] = 3;        cost[2][1] = 1;        cost[2][2] = 0;        cost[2][3] = 2;        cost[3][0] = 7;        cost[3][1] = 999;        cost[3][2] = 2;        cost[3][3] = 0;        entity = new Entity[NUMENTITIES];        entity[0] = new Entity0();        entity[1] = new Entity1();        entity[2] = new Entity2();        entity[3] = new Entity3();        if (linkChanges)        {            eventList.add(new Event(10000.0, LINKCHANGE, 0));        }    }        // Starts the simulation. It will end when no more packets are in the    // medium    public void runSimulator()    {        Event next;        Packet p;                while(true)        {            next = eventList.removeNext();                        if (next == null)            {                break;            }                        if (traceLevel > 1)            {                System.out.println();                System.out.println("main(): event received.  t=" +                                   next.getTime() +", node=" +                                    next.getEntity());                if (next.getType() == FROMLAYER2)                {                    p = next.getPacket();                    System.out.print("  src=" + p.getSource() + ", ");                    System.out.print("dest=" + p.getDest() + ", ");                    System.out.print("contents=[");                    for (int i = 0; i < NUMENTITIES - 1; i++)                    {                        System.out.print(p.getMincost(i) + ", ");                    }                    System.out.println(p.getMincost(NUMENTITIES - 1) + "]");                }                else if (next.getType() == LINKCHANGE)                {                    System.out.println("  Link cost change.");                }            }                        time = next.getTime();                        if (next.getType() == FROMLAYER2)            {                p = next.getPacket();                if ((next.getEntity() < 0) || (next.getEntity() >= NUMENTITIES))                {                    System.out.println("main(): Panic. Unknown event entity.");                }                else                {                    entity[next.getEntity()].update(p);                }            }            else if (next.getType() == LINKCHANGE)            {                if (time < 10001.0)                {                    cost[0][1] = 20;                    cost[1][0] = 20;                    entity[0].linkCostChangeHandler(1, 20);                    entity[1].linkCostChangeHandler(0, 20);                }                else                {                    cost[0][1] = 1;                    cost[1][0] = 1;                    entity[0].linkCostChangeHandler(1, 1);                    entity[1].linkCostChangeHandler(0, 1);                }            }            else            {                System.out.println("main(): Panic.  Unknown event type.");            }            }                System.out.println("Simulator terminated at t=" + time +                           ", no packets in medium.");            }        // Sends a packet into the medium    /**** Warning!  This will allow an entity to send packets that they          couldn't possibly send (e.g. Entity 1 could send a packet from          0 to 3).  This should be fixed later... ****/    public static void toLayer2(Packet p)    {        Packet currentPacket;        double arrivalTime;            if ((p.getSource() < 0) || (p.getSource() >= NUMENTITIES))        {            System.out.println("toLayer2(): WARNING: Illegal source id in " +                               "packet; ignoring.");            return;        }        if ((p.getDest() < 0) || (p.getDest() >= NUMENTITIES))        {            System.out.println("toLayer2(): WARNING: Illegal destination id " +                               "in packet; ignoring.");            return;        }        if (p.getSource() == p.getDest())        {            System.out.println("toLayer2(): WARNING: Identical source and " +                               "destination in packet; ignoring.");            return;        }        if (cost[p.getSource()][p.getDest()] == 999)        {            System.out.println("toLayer2(): WARNING: Source and destination " +                               "not connected; ignoring.");            return;        }                        if (traceLevel > 2)        {            System.out.println("toLayer2(): source=" + p.getSource() +                                " dest=" + p.getDest());            System.out.print("             costs:");            for (int i = 0; i < NUMENTITIES; i++)            {                System.out.print(" " + p.getMincost(i));            }            System.out.println();        }                arrivalTime = eventList.getLastPacketTime(p.getSource(), p.getDest());        if (arrivalTime == 0.0)        {            arrivalTime = time;        }        arrivalTime = arrivalTime + 1.0 + (rand.nextDouble() * 9.0);                if (traceLevel > 2)        {            System.out.println("toLayer2(): Scheduling arrival of packet.");        }        currentPacket = new Packet(p);        eventList.add(new Event(arrivalTime, FROMLAYER2,                                 currentPacket.getDest(), currentPacket));    }}