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Chapter 3: GridWorld Classes and Interfaces

Main classes are:  Location – Class  Grid of Actors - Interface BoundedGrid of Actors - Class UnboundedGrid of Actors - Class  Actor – Class Bug – Class Flower – Class Rock - Class Location > Grid AbstractGrid BoundedGrid UnboundedGrid Actor implements uses extends Bug extends FlowerRock uses

Location Class Encapsulates the coordinates for an actor’s position in a grid  Row and Column number Rows increase going down Columns increase going right  Also has methods that determine relationships between locations and compass directions  Every actor has a direction 0 for north, 45 is northeast, …  Location class also has eight constants that specify the constant direction NORTH, NORTHEAST, …

Location Class public Location(int r, int c) constructs a location with row r and column c public int getRow() returns the row of this location public int getCol() returns the column of this location public Location getAdjacentLocation(int direction) returns the adjacent location in the compass direction that is closest to direction public int getDirectionToward(Location target) returns the closest compass direction from this location toward target Testable API

Location Class public boolean equals(Object other) returns true if other is a Location object with the same row and column values as this location, and false otherwise public int hashCode() returns a hash code (unique key) for this location public int compareTo(Object otherObject) returns a negative integer if this location is less than other (if the row is less than other.row or if the rows are equal and column is less than other.column), zero if the two locations are equal, or a positive integer if this location is greater than other. Locations are ordered in row-major order public String toString() returns a string with the row and the column of this location, in the format (row, col) Testable API

Location Class Compass directions: public static final int NORTH = 0; public static final int EAST = 90; public static final int SOUTH = 180; public static final int WEST = 270; public static final int NORTHEAST = 45; public static final int SOUTHEAST = 135; public static final int SOUTHWEST = 225; public static final int NORTHWEST = 315;

Location Class Turn angles: public static final int LEFT = -90; public static final int RIGHT = 90; public static final int HALF_LEFT = -45; public static final int HALF_RIGHT= 45; public static final int FULL_CIRCLE = 360; public static final int HALF_CIRCLE = 180 ; public static final int AHEAD = 0;

Examples Location loc1 = new Location(5,7); Location locOrig = new Location(0,0); Location loc2 = loc1.getAdjacentLocation(Location.WEST); // (5,6) Location loc3 = loc1.getAdjacentLocaton(Location.NORTHEAST); // (4,8) Location loc4 = locOrig.getAdjacentLocaton(Location.WEST); // (0,-1) int dir = loc1.getDirectionToward(new Location(6,8)); // 135

Turning by an Amount You may have been using multiple calls to the turn() method to turn an Actor  We can use setDirection and Location constants for this instead  setDirection(getDirection() + Location.HALF_RIGHT); // turn 45 degrees

Exercise Set 3 Location loc1 = new Location(4, 3); Location loc2 = new Location(3, 4); 1. How would you access the row value of loc1 ? loc1.getRow() 2. What is the value of b after the following statement is executed? boolean b = loc1.equals(loc2); false 3. What is the value of loc3 after the following? Location loc3 = loc2.getAdjacentLocation(Location.SOUTH); (4, 4) 4. What is the value of dir after the following? int dir = loc1.getDirectionToward(new Location(6,1)); 225 5. How does the getAdjacentLocation method know which location to return? It first takes the direction passed to it and converts it to the closest 45 degree direction. Then it looks in that direction to return the adjacent location

Grid is an interface that details the behaviors expected of a grid. All its methods are abstract methods (no code). Grid was designed as an interface because many different structures could be used to store the grid values. An interface works perfectly in this case due to the large number of unknowns.

© A+ Computer Science - www.apluscompsci.com Grid abstract methods NameUse get(loc)returns the object reference at location loc getEmptyAdjacentLocations(loc)returns an ArrayList of the valid empty locations in 8 directions getNeighbors(loc)returns an ArrayList of the objects around location loc getNumCols()returns the number of columns in this grid getNumRows()returns the number of rows in this grid getOccupiedAdjacentLocations(loc)returns an ArrayList of the valid locations in 8 directions that contain objects getOccupiedLocations()returns an ArrayList of locations in the entire grid that contain objects import info.gridworld.grid.Grid; Note: loc is a reference to a Location object.

© A+ Computer Science - www.apluscompsci.com Grid abstract methods (continued) NameUse getValidAdjacentLocations(loc)returns an ArrayList of the valid locations in 8 directions isValid(loc)checks to see if location is valid (returns true/false) put(loc, obj)puts the obj in grid at location loc. Returns the object that was previously in the location. Note: If you want to add Actors to a world, then don’t use grid.put() since it will not update the location of the Actor. Use world.add() instead. remove(loc)takes the object at location loc out of the grid. Returns the object that was removed. Note: Use world.remove() instead of grid.remove() when removing Actors. import info.gridworld.grid.Grid; Note: loc is a reference to a Location object. obj is a reference to an Object.

Grid Interface int getNumRows() returns the number of rows, or -1 if this grid is unbounded int getNumCols() returns the number of columns, or -1 if this grid is unbounded Boolean isValid(Location loc) returns true if loc is valid in this grid, false otherwise precondition: loc is not null E put(Location loc, E obj) puts obj at location loc in this grid and returns the object previously at that location (or null if the location was previously empty) precondition: loc is valid in this grid and obj is not null Testable API E stands for Object

Grid Interface E remove(Location loc) removes the object at location loc and returns it (or null if the location is unoccupied) precondition: loc is valid in this grid E get(Location loc) returns the object at location loc (or null if the location is unoccupied) precondition: loc is valid in this grid ArrayList getOccupiedLocations() returns all occupied locations in this grid ArrayList getValidAdjacentLocations(Location loc) returns all valid locations adjacent to loc in this grid. The Array list is populated by going clockwise beginning at the adjacent north location precondition: loc is valid in this grid Testable API

Grid Interface ArrayList getEmptyAdjacentLocations(Location loc) returns all valid empty locations adjacent to loc in this grid precondition: loc is valid and in this grid ArrayList getOccupiedAdjacentLocations(Location loc) returns all valid occupied locations adjacent to loc in this grid precondition: loc is valid in this grid ArrayList getNeighbors(Location loc) returns all objects in the occupied locations adjacent to loc in this grid precondition: loc is valid in this grid Note: All the Grid methods that look at adjacent locations and return an array list will populate the array list by first looking at the adjacent north location and then going clockwise to retrieve all applicable locations Testable API

Exercise Answers Set 4 Assume we have a BoundedGrid reference named grid. 1. How can you get a count of the objects in the grid?  grid.getOccupiedLocations().size() 2. How can you get a count of the empty locations in the grid?  grid.getNumRows() * grid.getNumCols() – grid.getOccupiedLocations.size() 3. How can you check if location (10,10) is in the grid?  if (grid.isValid(new Location(10,10))) 4. Grid contains method declarations but no code. Why?  It is an interface 5. Where can you find the code for the methods?  In the classes that implement the interface: BoundedGrid and UnboundedGrid 6. All methods that can return multiple objects return them in an ArrayList. Would it have been a better design to return them in an array? Explain your answer.  ArrayLists are arrays that can grow or shrink. They are better than arrays when you don’t know how many items you will have.

© A+ Computer Science - www.apluscompsci.com BoundedGrid grid; grid = new BoundedGrid (5,5); grid.put(new Location(2,2),4); grid.put(new Location(1,1),11); System.out.println(grid); System.out.println(grid.isValid(new Location(-2,3))); System.out.println(grid.isValid(new Location(2,3))); OUTPUT {(1, 1)=11, (2, 2)=4} false true 11 4

© A+ Computer Science - www.apluscompsci.com BoundedGrid grid; grid = new BoundedGrid (5,5); grid.put(new Location(2,2),4); grid.put(new Location(1,1),11); grid.put(new Location(0,2),3); grid.put(new Location(0,1),6); System.out.println(grid); grid.remove(new Location(1,1)); System.out.println(grid); grid.remove(new Location(1,1)); System.out.println(grid); World world = new World(grid); world.show(); OUTPUT {(0, 1)=6, (0, 2)=3, (1, 1)=11, (2, 2)=4} {(0, 1)=6, (0, 2)=3, (2, 2)=4}

UnboundedGrid grid; grid = new UnboundedGrid (); System.out.println(grid.getNumRows()); System.out.println(grid.getNumCols()); System.out.println(grid); World world = new World(grid); world.show(); OUTPUT {}

UnboundedGrid grid; grid = new UnboundedGrid (); grid.put(new Location(2,2),4); grid.put(new Location(1,1),11); System.out.println(grid); System.out.println(grid.isValid(new Location(-2,3))); System.out.println(grid.isValid(new Location(2,3))); World world = new World(grid); world.show(); OUTPUT {(1, 1)=11, (2, 2)=4} true 11 4

© A+ Computer Science - www.apluscompsci.com UnboundedGrid grid; grid = new UnboundedGrid (); grid.put(new Location(2,2),4); grid.put(new Location(1,1),11); grid.put(new Location(0,2),3); grid.put(new Location(0,1),6); grid.put(new Location(-2,-2),-2); System.out.println(grid); grid.remove(new Location(1,1)); System.out.println(grid); grid.remove(new Location(1,1)); System.out.println(grid); World world = new World(grid); world.show(); OUTPUT {(0, 1)=6, (0, 2)=3, (-2, -2)=-2, (2, 2)=4, (1, 1)=11} {(0, 1)=6, (0, 2)=3, (-2, -2)=-2, (2, 2)=4}

World frequently used methods NameUse World()creates a new world using 10X10 grid World(grid)creates a new world using grid add(loc, obj)add obj to world at location loc show()makes the world visible import info.gridworld.world.World;

© A+ Computer Science - www.apluscompsci.com World world = new World (); world.add(new Location(0,0), new Monster()); world.add(new Location(9,0), new Monster()); world.show(); or Grid grid = new BoundedGrid (10,10); World world = new World(grid); grid.put(new Location(0,0), new Monster()); grid.put(new Location(9,0), new Monster()); world.show();

World frequently used methods NameUse getGrid()returns a reference to the world’s grid remove(loc)removes the object at location loc locationClicked(loc)activated by a mouse click in the grid. Returns boolean (true). You can control what happens when clicking a cell. import info.gridworld.world.World;

© A+ Computer Science - www.apluscompsci.com BoundedGrid grid; grid = new BoundedGrid (5,5); grid.put(new Location(2,2),4); grid.put(new Location(1,1),9); grid.put(new Location(0,4),11); grid.put(new Location(4,3),5); grid.put(new Location(2,0),1); World world; world = new World (grid); world.show();

© A+ Computer Science - www.apluscompsci.com World world; world = new World (new BoundedGrid(6,6)); world.show(); Grid grid = world.getGrid(); for(int r=0; r<grid.getNumRows(); r++) { for(int c=0; c<grid.getNumCols(); c++) { grid.put(new Location(r,c), new Monster(r,c,2)); }

© A+ Computer Science - www.apluscompsci.com import info.gridworld.world.World; import info.gridworld.grid.Location; public class RowColMultiplyWorld extends World { public boolean locationClicked(Location loc) { add(loc, new RowColMultiplyBug(loc.getCol()*loc.getRow())); System.out.println("Location "+loc+" clicked"); return true; }

Actor Class public Actor() constructs a blue actor that is facing north public Color getColor() returns the color of this actor public void setColor(Color newColor) sets the color of this actor to newColor public int getDirection() returns the direction of this actor, an angle between 0 and 359 degrees public void setDirection(int newDirection) sets the direction of this actor to the angle between 0 a nd 359 degrees that is equivalent to newDirection Testable API

Actor Class public Grid getGrid() returns the grid of this actor, or null if this actor is not contained in the grid public Location getLocation() returns the location of this actor precondition: this actor is contained in this grid public void putSelfInGrid(Grid gr, Location loc) puts this actor into the location loc of the grid gr. If there is another actor at loc, it is removed. precondition: this actor is not contained in a grid and loc is valid in gr public void removeSelfFromGrid() removes this actor from its grid precondition: this actor is contained in a grid Testable API

Actor Class public void moveTo(Location newLocation) moves this actor to newLocation. If there is another actor at newLocation, it is removed. precondition: this actor is contained in a grid and newLocation is valid in the grid of this actor public void act() reverses the direction of this actor. Override this method in subclasses of Actor to define types of actors with different behavior public String toString() returns a string with the location, direction, and color of this actor Testable API

Rock and Flower Classes Subclasses of Actor  Override act() Rocks don’t do anything in the act method  Empty body {} Flowers change the color  Reduces the red, green, and blue by the same amount (0.05)  Gets darker Testable API

Exercise Set 5 1. Name 3 properties that every Actor has.  Color, direction, location 2. When an actor is constructed what is its direction and color?  Blue and North 3. Why was the Actor class created as a class and not an interface?  Use classes or abstract classes when we want to provide fields and methods. Interfaces can only define constants and abstract methods. 4. Can an Actor put itself in the grid twice without removing itself?  No, you will get an IllegalStateException 5. Can an Actor remove itself from the grid twice?  No, you will get an IllegalStateException 6. Can an actor place itself in the grid and then remove itself and then add itself to the grid? Try it. What happens?  Should work. 7. How can an actor turn 90 degrees to the right?  setDirection(getDirection() + Location.RIGHT);

Bug Class Extends Actor In act() check if can move and if can move, move, and drop a flower in the old location, else turn (45 degrees) Implementation Testable

Bug Class public class Bug extends Actor { public Bug() { setColor(Color.RED); } /** * Constructs a bug of a given color. * @param bugColor the color for this bug */ public Bug(Color bugColor) { setColor(bugColor); } Implementation

Bug Class public void act() { if (canMove()) move(); else turn(); } /* Turns the bug 45 degrees to the right without changing its location. */ public void turn() { setDirection(getDirection() + Location.HALF_RIGHT); } Implementation

Bug Class /** * Moves the bug forward, putting a flower into the location it previously occupied. */ public void move() { Grid gr = getGrid(); if (gr == null) return; Location loc = getLocation(); Location next = loc.getAdjacentLocation(getDirection()); if (gr.isValid(next)) moveTo(next); else removeSelfFromGrid(); Flower flower = new Flower(getColor()); flower.putSelfInGrid(gr, loc); } Implementation

Bug Class /** * Tests whether this bug can move forward into a location that is empty or * contains a flower. * @return true if this bug can move. */ public boolean canMove() { Grid gr = getGrid(); if (gr == null) return false; Location loc = getLocation(); Location next =loc.getAdjacentLocation(getDirection()); if (!gr.isValid(next)) return false; Actor neighbor = gr.get(next); return (neighbor == null)||(neighbor instanceof Flower); // ok to move into empty location or onto flower // not ok to move onto any other actor } Implementation

Exercise Set 6 1. Which statement in the canMove() method ensures that a bug doesn’t move out of the grid? if (!gr.isValid(next)) 2. Which statement in the canMove() method keeps a bug from walking into a rock? return (neighbor == null) || (neighbor instanceof Flower); 3. Which methods from the Grid interface are invoked in the canMove() method and why? isValid() is used to check if the location in front of the bug is valid get() is used to get the object in the grid in front of the bug 4. Which method in the Location class is invoked in the canMove() method and why? getAdjacentLocation() is used to get the location in front of the bug 5. Which methods inherited from the Actor class are invoked in the canMove() method and why? getGrid() is used to check that the bug is in a grid getLocation() is used to get the current location of the bug getDirection() is used to find the adjacent location in front of the bug

Exercise Set 6 6. What happens in the move method when the location in front of the bug is out of the grid? The bug removes itself from the grid 7. Is the variable loc needed in the move method or could it be avoided by calling getLocation() multiple times? It is needed to store the previous location so that a flower can be put there 8. Why do you think that the flowers that are dropped by the bug have the same color as the bug? To make it clear which bug they come from 9. When a bug removes itself from the grid, will it place a flower in its previous location? Yes 10. Which statement in the move() method places a flower in the grid at the previous location? flower.putSelfInGrid(gr, loc); 11. If a bug needs to turn 180 degrees how many times should it call the turn() method? 180 / 45 = 4

The Graphical User Interface The World class connects the described classes and the GUI  The GUI asks the World for the grid, gets the objects in the grid, and draws them at their locations This happens when the World’s show() method is executed.  ActorWorld is a subclass of World That has a step() method that calls act() on each object in the Grid Has methods for adding objects  public void add(Location loc, Actor theActor)  public void add(Actor theActor)  Adds the actor to a random location Has a method for removing objects  Public Actor remove(Location loc) optional

step() method in ActorWorld class public void step() { Grid gr = getGrid(); ArrayList actors = new ArrayList (); for (Location loc : gr.getOccupiedLocations()) actors.add(gr.get(loc)); for (Actor a : actors) { // only act if another actor hasn't removed a if (a.getGrid() == gr) a.act(); }

Class Diagram

Jumper Activity In groups of 3 Create a Jumper class. Objects of this class can move forward 2 cells and can jump over rocks or flowers. They don’t leave anything behind.  Discuss the following and put the answers to these questions in comments at the beginning of the program: What happens if the next location is empty but the location two in front contains a rock or flower? What should happen if the location two in front is out of the grid? What should a Jumper do if it is facing the edge of the grid? What should a Jumper do if the location two in front has another Actor in it (not a Flower or Rock) What will a Jumper do if it encounters another Jumper? Are there any other tests a Jumper needs to make?

Jumper Activity Cont. Consider the following design issues:  Which class should Jumper extend?  Is there an existing class that is similar to Jumper?  Should you create a constructor? What parameters should it have?  Which methods should be overridden?  What new methods should be added?  How will you test the class? Code the Jumper and JumperRunner classes Test the Jumper class  Or give it to another group to test

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