Grid.java

/*
 * 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;

/**
 * <code>Grid</code> provides an interface for a two-dimensional, grid-like
 * environment containing arbitrary objects. <br />
 * This interface is testable on the AP CS A and AB exams.
 */
public interface Grid<E>
{
    /**
     * Returns the number of rows in this grid.
     * @return the number of rows, or -1 if this grid is unbounded
     */
    int getNumRows();

    /**
     * Returns the number of columns in this grid.
     * @return the number of columns, or -1 if this grid is unbounded
     */
    int getNumCols();

    /**
     * Checks whether a location is valid in this grid. <br />
     * Precondition: <code>loc</code> is not <code>null</code>
     * @param loc the location to check
     * @return <code>true</code> if <code>loc</code> is valid in this grid,
     * <code>false</code> otherwise
     */
    boolean isValid(Location loc);

    /**
     * Puts an object at a given location in this grid. <br />
     * Precondition: (1) <code>loc</code> is valid in this grid (2)
     * <code>obj</code> is not <code>null</code>
     * @param loc the location at which to put the object
     * @param obj the new object to be added
     * @return the object previously at <code>loc</code> (or <code>null</code>
     * if the location was previously unoccupied)
     */
    E put(Location loc, E obj);

    /**
     * Removes the object at a given location from this grid. <br />
     * Precondition: <code>loc</code> is valid in this grid
     * @param loc the location of the object that is to be removed
     * @return the object that was removed (or <code>null<code> if the location
     *  is unoccupied)
     */
    E remove(Location loc);

    /**
     * Returns the object at a given location in this grid. <br />
     * Precondition: <code>loc</code> is valid in this grid
     * @param loc a location in this grid
     * @return the object at location <code>loc</code> (or <code>null<code>
     *  if the location is unoccupied)
     */
    E get(Location loc);

    /**
     * Gets the locations in this grid that contain objects.
     * @return an array list of all occupied locations in this grid
     */
    ArrayList<Location> getOccupiedLocations();

    /**
     * Gets the valid locations adjacent to a given location in all eight
     * compass directions (north, northeast, east, southeast, south, southwest,
     * west, and northwest). <br />
     * Precondition: <code>loc</code> is valid in this grid
     * @param loc a location in this grid
     * @return an array list of the valid locations adjacent to <code>loc</code>
     * in this grid
     */
    ArrayList<Location> getValidAdjacentLocations(Location loc);

    /**
     * Gets the valid empty locations adjacent to a given location in all eight
     * compass directions (north, northeast, east, southeast, south, southwest,
     * west, and northwest). <br />
     * Precondition: <code>loc</code> is valid in this grid
     * @param loc a location in this grid
     * @return an array list of the valid empty locations adjacent to
     * <code>loc</code> in this grid
     */
    ArrayList<Location> getEmptyAdjacentLocations(Location loc);

    /**
     * Gets the valid occupied locations adjacent to a given location in all
     * eight compass directions (north, northeast, east, southeast, south,
     * southwest, west, and northwest). <br />
     * Precondition: <code>loc</code> is valid in this grid
     * @param loc a location in this grid
     * @return an array list of the valid occupied locations adjacent to
     * <code>loc</code> in this grid
     */
    ArrayList<Location> getOccupiedAdjacentLocations(Location loc);

    /**
     * Gets the neighboring occupants in all eight compass directions (north,
     * northeast, east, southeast, south, southwest, west, and northwest).
     * <br />
     * Precondition: <code>loc</code> is valid in this grid
     * @param loc a location in this grid
     * @return returns an array list of the objects in the occupied locations
     * adjacent to <code>loc</code> in this grid
     */
    ArrayList<E> getNeighbors(Location loc);
}