BoundedGrid

package feAttempt;

/*
 * AP(r) Computer Science GridWorld Case Study:
 * Copyright(c) 2002-2006 College Entrance Examination Board
 * (http://www.collegeboard.com).
 *
 * This code is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * @author Alyce Brady
 * @author APCS Development Committee
 * @author Cay Horstmann
 */

import java.util.ArrayList;

/**
 * A <code>BoundedGrid</code> is a rectangular grid with a finite number of
 * rows and columns. <br />
 * The implementation of this class is testable on the AP CS AB exam.
 */
public class BoundedGrid<E> extends AbstractGrid<E>
{
  private Object[][] occupantArray; // the array storing the grid elements

  /**
   * Constructs an empty bounded grid with the given dimensions.
   * (Precondition: <code>rows > 0</code> and <code>cols > 0</code>.)
   * @param rows number of rows in BoundedGrid
   * @param cols number of columns in BoundedGrid
   */
  public BoundedGrid(int rows, int cols)
  {
    if (rows <= 0)
      throw new IllegalArgumentException("rows <= 0");
    if (cols <= 0)
      throw new IllegalArgumentException("cols <= 0");
    occupantArray = new Object[rows][cols];
  }

  public int getNumRows()
  {
    return occupantArray.length;
  }

  public int getNumCols()
  {
    // Note: according to the constructor precondition, numRows() > 0, so
    // theGrid[0] is non-null.
    return occupantArray[0].length;
  }

  public boolean isValid(Location loc)
  {
    return 0 <= loc.getRow() && loc.getRow() < getNumRows()
      && 0 <= loc.getCol() && loc.getCol() < getNumCols();
  }

  public ArrayList<Location> getOccupiedLocations()
  {
    ArrayList<Location> theLocations = new ArrayList<Location>();

    // Look at all grid locations.
    for (int r = 0; r < getNumRows(); r++)
    {
      for (int c = 0; c < getNumCols(); c++)
      {
        // If there's an object at this location, put it in the array.
        Location loc = new Location(r, c);
        if (get(loc) != null)
          theLocations.add(loc);
      }
    }

    return theLocations;
  }

  public E get(Location loc)
  {
    if (!isValid(loc))
      throw new IllegalArgumentException("Location " + loc
                                           + " is not valid");
    return (E) occupantArray[loc.getRow()][loc.getCol()]; // unavoidable warning
  }

  public E put(Location loc, E obj)
  {
    if (!isValid(loc))
      throw new IllegalArgumentException("Location " + loc
                                           + " is not valid");
    if (obj == null)
      throw new NullPointerException("obj == null");

    // Add the object to the grid.
    E oldOccupant = get(loc);
    occupantArray[loc.getRow()][loc.getCol()] = obj;
    return oldOccupant;
  }

  public E remove(Location loc)
  {
    if (!isValid(loc))
      throw new IllegalArgumentException("Location " + loc
                                           + " is not valid");

    // Remove the object from the grid.
    E r = get(loc);
    occupantArray[loc.getRow()][loc.getCol()] = null;
    return r;
  }
}