public abstract class Entity{    // Each entity will have a distance table    protected int[][] distanceTable = new int[NetworkSimulator.NUMENTITIES]                                           [NetworkSimulator.NUMENTITIES];        // The update function.  Will have to be written in subclasses by students    public abstract void update(Packet p);        // The link cost change handlder.  Will have to be written in appropriate    // subclasses by students.  Note that only Entity0 and Entity1 will need    // this, and only if extra credit is being done    public abstract void linkCostChangeHandler(int whichLink, int newCost);    // Print the distance table of the current entity.    protected abstract void printDT();}