Mine

import java.util.*;
public class SMBE extends SquareEnvironment
{
  private LinkedList[] steveirwin;
  private int numcols;
  public SMBE(int r, int c)
  {
    super();
    numcols = c;
    steveirwin = new LinkedList[r];
    int i;
    for(i = 0; i < r; i++)
      steveirwin[i] = new LinkedList();
  }
  public int numRows()
  {
    return steveirwin.length;
  }
  public int numCols()
  {
    return numcols;
  }
  public boolean isValid(Location loc)
  {
    if(loc == null)
      return false;
    return (0 <= loc.row() && loc.row() < numRows()) &&
           (0 <= loc.col() && loc.col() < numCols());
  }
  public int numObjects()
  {
    return objectCount;
  }
  public Locatable[] allObjects()
  {
    Locatable[] theObjects = new Locatable[numObjects()];
    int tempObjectCount = 0;
    for(int r = 0; r < numRows(); r++)
    {
      for ( int c = 0; c < numCols(); c++ )
      {
        Locatable obj = theGrid[r][c];
        if(obj != null)
        {
          theObjects[tempObjectCount] = obj;
          tempObjectCount++;
        }
      }
    }
    return theObjects;
  }
  public boolean isEmpty(Location loc)
  {
    return isValid(loc) && objectAt(loc) == null;
  }
  public Locatable objectAt(Location loc)
  {
    if(!isValid(loc))
      return null;
    return theGrid[loc.row()][loc.col()];
  }
  public String toString()
  {
    Locatable[] theObjects = allObjects();
    String s = "Environment contains " + numObjects() + " objects: ";
    for(int index = 0; index < theObjects.length; index++)
      s += theObjects[index].toString() + " ";
    return s;
  }
  public void add(Locatable obj)
  {
    Location loc = obj.location();
    if(!isEmpty(loc))
      throw new IllegalArgumentException("Location " + loc +
                                    " is not a valid empty location");
    theGrid[loc.row()][loc.col()] = obj;
    objectCount++;
  }
  public void remove(Locatable obj)
  {
    Location loc = obj.location();
    if(objectAt(loc) != obj)
      throw new IllegalArgumentException("Cannot remove " + 
                                               obj + "; not there");
    theGrid[loc.row()][loc.col()] = null;
    objectCount--;
  }
  public void recordMove(Locatable obj, Location oldLoc)
  {
    Location newLoc = obj.location();
    if(newLoc.equals(oldLoc))
      return;
    Locatable foundObject = objectAt(oldLoc);
    if(!(foundObject == obj && isEmpty(newLoc)))
      throw new IllegalArgumentException("Precondition violation moving "
                + obj + " from " + oldLoc);
    theGrid[newLoc.row()][newLoc.col()] = obj;
    theGrid[oldLoc.row()][oldLoc.col()] = null;
  }
}