GridWorld Case Study

1. GridWorld Case Study

2. Overview • Simulates actions and interactions of objects in a two-d grid • Actors are displayed by a GUI • Can add new actors to the grid and invoke methods on all actors • Each actor ‘acts’ in a specified way

3. The Class Hierarchy

4. The Actors and their Actions • Rock – does nothing • Flower – darkens its color • Bug – moves forward if it can. It can move into an empty spot or onto a flower. When it moves, it deposits a flower in its previous location. If it moves to a location occupied by a flower, that flower is removed from the grid. A bug can’t move if it is blocked in front by either another non-flower actor or the edge of the grid. When a bug is prevented from moving, it turns 45⁰ to the right. • BoxBug – Moves like a bug. Additionally, if it encounters no obstacles, it traces out a square of flowers with a given side length. If a BoxBug is blocked from moving, it makes two right turns and starts again.

5. The Actors and their Actions continued • Critter – gets a list of its adjacent neighboring actors and processes them by “eating” each actor is not a rock or another Critter. It then randomly selects one of the empty neighboring locations and moves there. If there are no available empty locations, a critter does not move. • ChameleonCritter – gets a list of adjacent neighbors, randomly picks on of them, and changes its color to that of the selected actor. Moves like a Critter, but additionally, it first changes its direction to face its new location before moving.

6. Location Class • Encapsulates row and column values for any position in the grid • Provides constants for compass directions and turn angles • Provides methods for determining relationships between locations and compass directions

7. Location Constants Constants that represent compass directions: Constants that represent commonly used turn angles

8. Location Methods • public Location(int r, int c) – constructs a Location with given row and column • Accessors • public intgetRow() • public intgetColumn() • public Location getAdjascentLocation(int direction) – returns the adjascent location in the compass direction closest to direction • public intgetDirectionToward(Location target) – returns the direction, rounded to the nearest compass direction, from this location toward a target location • public intgetHashCode() – generates and returns a hash code for this Location • Comparison methods • public boolean equals(Object other) • public intcompareTo(Object other) – by row first, then left to right • public String toString() – form (row, col)

9. Actor Class • Superclass for every creature • HAS-A location, direction, and color • Has the ability to put itself in the grid and remove itself from the grid • Actor is a black-box class

10. Actor public methods • public Actor() – default constructor; blue actor facing north • Accessors • public Color getColor() • public intgetDirection() • public Location getLocation() • public Grid<Actor> getGrid() – returns null if actor is not in grid • Mutators • public void setColor(Color newColor) • public void setDirection(intnewDirection) • public void moveTo(Location newLocation) • If new location is occupied, actor in that location is removed from grid • Preconditions: • This Actor is in a grid • newLocation is valid in this Actor’s grid

11. Actor public methods continued • public void putSelfInGrid(Grid<Actor> gr, Location loc) • Precondition: loc is valid • public void removeSelfFromGrid() • public void act() • Reverses direction of this actor • This method is often overridden in subclasses • public String toString() • Returns a String with the location, direction, and color of this Actor

12. Rock Class • Acts by doing nothing (act() is overridden with empty method body) • Default constructor that creates a black rock • Second constructor that allows construction of a Rock with a specified color

13. Flower Class • Acts by darkening its color (act() is overridden; reduces values of the red, green, and blue components of its color by a constant factor) • Default constructor that creates a pink flower • Second constructor that allows construction of a flower with a specified color

14. Bug Class • Moves forward in a straight line • Turns only if it is blocked • Can be blocked by the edge of the grid or a non-Flower actor • Any flower in the bug’s path is removed from the grid

15. Bug public methods • public Bug() – default constructor; constructs a red Bug • public Bug(Color bugColor) – constructs a Bug with specified color • public void act() – turns bug 45⁰ to the right without changing location (adds Location.HALF_RIGHTto bug’s current direction) • public booleancanMove() • Returns true if: • Location directly in front of it is valid • Location directly in front of it is empty or contains a flower • public void move() – moves bug forward, places a flower that is the color of the bug in its previous location

16. BoxBug Class • IS-A Bug that moves in a square pattern if unimpeded • Two private instance variables • sideLength – number of steps in a side of its square • steps – keeps track of where the BoxBug is in creating a side; gets reset to 0 when a side has been completed or if the bug must start again after encountering an obstacle

17. BoxBug public methods • public BoxBug(int length) – constructor; sets sideLength to length; initializes steps to 0 • public void act() – overridden method performs one step in the creation of the BoxBug’s square • Steps for making the square: • act() method tests whether the bug is still in the process of making a side – if(steps < sideLength)… • If this is true, and the bug can move, the bug moves and steps is incremented • If this is false, the bug turns by calling turn() twice – then, steps is reset to 0 • If steps < sideLength is true but canMove() is false, the same preparation for a new side occurs (turn, turn, reset steps) • If BoxBug is unimpeded in making its square, and sideLength is k, there will be k+1 flowers on each side of the square

18. Critter Class • IS-A actor with the following behavior: • Get a list of neighboring actors • Process the actors • Get a list of possible locations to move to • Select a location from the list • Move there • No explicit constructor, thus default Actor constructor used (blue Critter facing North)

19. Critter public methods • public void act() – gets a list of neighbors, processing them, gets a list of possible locations to move to, selects one of these, moves to selected location • public ArrayList<Actor> getActors() – returns a list of adjacent actors • public void processActors(ArrayList<Actor> actors) – processes actors; Critter “eats” all actors that are not rocks or other critters. • public ArrayList<Location> getMoveLocations() – returns a list of valid, adjacent, empty, neighboring locations, which are the possible locations for the next move. Grid method getEmptyAdjacentLocations() is used, with the critter’s current location as its parameter • public Location selectMoveLocation(ArrayList<Location> locs) – • Assign n to length of list • If n == 0, return current location of critter • Get random int from 0 to n – 1 (int r = (int)(Math.random() * n)) • Return locs.get(r) • public void makeMove(Location loc) – moves Critter to specified Location • Precondition: loc is valid • Implemented with moveTo() in Actor

20. ChameleonCritter Class • IS-A Critter • Instead of eating neighbors, it randomly selects one actor and changes its color to that of the selected actor • Moves like a Critter with one difference, before it moves it turns to face its new location

21. ChameleonCritter public methods • public void processActors(ArrayList<Actor> actors) – randomly selects adjacent neighbor, changes its color to that of selected actor. Does nothing if no neighbors exist • public void makeMove(Location loc) – moves like Critter, but faces new location before it moves • setDirection() is used • getLocation().getDirectionToward(loc) used as parameter for setDirection()