1. AP "Case Studies" A big program for AP students to understand
Approximately 20% of the possible points on the AP exam will come from case study questions
First Case Study introduced in 1994:
Directory Manager (Pascal)
Big Int (C++)
Marine Biology (C++)
Marine Biology Simulation (Java)
GridWorld (Java) New for 2008!

2. The Program Actors (e.g. Bugs, Rocks) are placed into a grid
Each actor has a variety of attributes and behaviors
Students modify actors and create new ones
Jamie enhances the master/apprentice relationship aspect; provides information when Pat is confused, makes some suggestions showing great foresight, and, at the end, even offers to make needed changes to the graphical user interface.

3. The Chapters AB Experiment with existing program (run it)
Write new classes that extend Bug
Explore code needed to create actors
Write new classes that extend Critter
Grid data structures
Chap 5: Alternative representations
* interfaces
* follow-up part-time job during school year
* AB only AB

4. Bug.java The code for the Bugs is "buried" in the framework folder
The Bug class has:
a couple constructors
act()
turn()
move()
canMove()

5. Bug.java
public void act() {
if (canMove())
move();
else
turn(); }

6. BoxBug.java The code for the BoxBugs is in the Projects folder
public class BoxBug extends Bug {
private int steps;
private int sideLength;
// and more java

7. BoxBug.java public BoxBug(int length) { steps = 0;
sideLength = length; }
//Note: sideLength is measured from
//the centers of the grid cells, so
//BoxBug(3) will leave 4 flowers on
//each side

8. extending Bug In Chapter 2 you will extend Bug to make: CircleBug
SpiralBug
ZBug
DancingBug

9. Runner classes constructs an ActorWorld and adds Actors to it
When you write a new Actor class, you will also need to write a new Runner class to test it out

10. Creating a new type of Bug
Add a new folder to the Projects folder
Save a copy of BoxBug to your new folder. Make sure to give it a new name that ends with .java

11. Creating a new type of Bug
Now save a copy of BoxBugRunner to your new folder. Make sure to also give it a new name that ends with .java
Change the code in the two java files to use the new class names
public class CircleBugRunner {
public static void main(String[] args)
ActorWorld world = new ActorWorld();
CircleBug bob = new CircleBug(6);
bob.setColor(Color.ORANGE);
world.add(new Location(5, 5), bob);
world.show(); }

12. Creating a new type of Bug
Before you run the program to test out your new Bug, choose Project | Project Properties and choose the correct runner class

13. Dancing Bugs
A DancingBug is constructed with an array argument (the workbook calls it a parameter)
public class CircleBugRunner {
public static void main(String[] args)
ActorWorld world = new ActorWorld();
int [] naTurns = {1,2,3};
DancingBug bob =
new DancingBug(naTurns);
bob.setColor(Color.ORANGE);
world.add(new Location(5, 5), bob);
world.show(); }

14. Dancing Bugs int [] naTurns = {1,2,3}; DancingBug bob =
new DancingBug(naTurns);
Everytime bob moves, he will first turn.
His first move he will turn once.
His second move he will turn twice
His third move he will turn 3 times
Then the pattern repeats
His fourth move he will turn once.
His fifth move he will turn twice
His sixth move he will turn 3 times

15. Before Move One

16. After Move One

17. After Move Two

18. After Move Three

19. Dancing Bugs Your dancing bug should work with any array of any length
int [] naTurns = {5,1,3,17,5};
DancingBug bob =
new DancingBug(naTurns);
You will need a DancingBug class, and a runner to test it

20. The DancingBug class public class DancingBug extends Bug {
private int steps;
private int[] naTurns;
public DancingBug(int [] naT)
steps = 0;
naTurns = naT; }
public void act()
???

21. The Location class Stores a location with a row and column
Location(int row, int col)
int getRow()
int getCol()
boolean equals(Object other)
String toString()
What would this display?
Location one = new Location(4,5);
Location two = new Location(3,5);
System.out.println(one);
System.out.println(
two.getCol()==one.getCol());
System.out.println(two.equals(one));

22. The Location class Directions are in degrees clockwise from north
Location.NORTH is 0 degrees
Location.NORTHEAST is 45 degrees
Location.EAST is 90 degrees
What would this display?
System.out.println(Location.SOUTH);
System.out.println(
Location.SOUTHEAST);

23. getAdjacentLocation()
What would this display?
Location loc1 =
new Location(4,2);
Location loc2 = loc1.getAdjacentLocation(
Location.NORTH);
System.out.println(loc2);

24. getDirectionToward()
What would this display?
Location loc1 =
new Location(4,2);
Location loc2 =
new Location(3,2);
int nDir =
loc1.getDirectionToward(loc2);
System.out.println(nDir);

25. What is the output of this program fragment?
Location loc1 = new Location(2,3);
Location loc2 = new Location(5,3);
int nDir = loc1.getDirectionToward(loc2);
System.out.println(nDir);
Location loc3 = loc1.getAdjacentLocation(nDir);
System.out.println(loc3);
int nDir2 = nDir + Location.LEFT;
System.out.println(nDir2);
int nDir3 = nDir2 + Location.HALF_CIRCLE;
System.out.println(nDir3);
Location loc4 = loc1.getAdjacentLocation(nDir3);
System.out.println(loc4);

26. The Grid interface Two classes implement Grid: BoundedGrid
UnboundedGrid

27. Unbounded Grid
Choose the type of grid from the World menu

28. Methods in the Grid interface
boolean isValid(Location loc)
E put(Location loc, E obj)
E remove(Location loc)
E get(Location loc)
ArrayList <Location> getOccupiedLocations()
ArrayList <Location> getValidAdjacentLocations(Location loc)
ArrayList <Location> getEmptyAdjacentLocations(Location loc)
ArrayList <Location> getOccupiedAdjacentLocations(Location loc)
ArrayList <Location> getNeighbors(Location loc)
int getNumRows()
int getNumCols()

29. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
System.out.println(theGrid.getNumRows());

30. What is the output? 10 The default grid is 10 x 10
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
System.out.println(theGrid.getNumRows()); 10
The default grid is 10 x 10

31. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
System.out.println(
theGrid.isValid(new Location(10,3)));

32. What is the output? false ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
System.out.println(
theGrid.isValid(new Location(10,3)));
false

33. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
System.out.println(
theGrid.get(new Location(3,3)));

34. What is the output?
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
System.out.println(
theGrid.get(new Location(3,3)));
BoxBug[location=(3, 3), direction=0, color=java.awt.Color[r=255,g=0,b=0]]

35. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
System.out.println(
theGrid.getNeigbors(new Location(2,3)));

36. What is the output?
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
System.out.println(
theGrid.getNeigbors(new Location(2,3)));
BoxBug[location=(3, 3), direction=0, color=java.awt.Color[r=255,g=0,b=0]]

37. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getNeighbors(new Location(2,3)));

38. What is the output?
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getNeighbors(new Location(2,3)));
[BoxBug[location=(1, 3),direction=0, color=java.awt.Color[r=255,g=0,b=0]],
BoxBug[location=(3, 3),direction=0, color=java.awt.Color[r=255,g=0,b=0]]]

39. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getOccupiedAdjacentLocations(
new Location(2,3)));

40. What is the output? [(1, 3), (3, 3)] Press any key to continue...
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getOccupiedAdjacentLocations(
new Location(2,3)));
[(1, 3), (3, 3)]
Press any key to continue...

41. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getEmptyAdjacentLocations(
new Location(2,3)));

42. What is the output? [(1, 4), (2, 4), (3, 4), (3, 2), (2, 2), (1, 2)]
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getEmptyAdjacentLocations(
new Location(2,3)));
[(1, 4), (2, 4), (3, 4),
(3, 2), (2, 2), (1, 2)]
Press any key to continue...

43. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getValidAdjacentLocations(
new Location(2,3)));

44. What is the output? [(1, 3), (1, 4), (2, 4), (3, 4),
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
System.out.println(
theGrid.getValidAdjacentLocations(
new Location(2,3)));
[(1, 3), (1, 4), (2, 4), (3, 4),
(3, 3), (3, 2), (2, 2), (1, 2)]
Press any key to continue...

45. What is the output? ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
Rock mrSimon = new Rock();
world.add(new Location(4,5), mrSimon);
System.out.println(
theGrid.getOccupiedLocations());

46. What is the output? [(1, 3), (3, 3), (4, 5)]
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
BoxBug bob = new BoxBug(2);
world.add(new Location(3,3), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(1,3), jane);
Rock mrSimon = new Rock();
world.add(new Location(4,5), mrSimon);
System.out.println(theGrid.getOccupiedLocations());
[(1, 3), (3, 3), (4, 5)]
Press any key to continue...

47. Practice Quiz Question: What is the output?
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
System.out.println(theGrid.getNumCols());
Bug bob = new BoxBug(2);
world.add(new Location(1,5), bob);
BoxBug jane = new BoxBug(2);
world.add(new Location(6,5), jane);
Rock mrSimon = new Rock();
world.add(new Location(4,5), mrSimon);
System.out.println(theGrid.getOccupiedLocations());
System.out.println(
theGrid.getEmptyAdjacentLocations(new Location(5,5)));
theGrid.getValidAdjacentLocations(new Location(0,4)));
theGrid.getValidAdjacentLocations(new Location(0,4)).size());

48. The Actor class
Actors have accessor methods that access the color, direction, Grid and Location
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
Bug bob = new BoxBug(3);
world.add(new Location(1,5), bob);
System.out.println(bob.getColor());
//java.awt.Color[r=255,g=0,b=0]
System.out.println(bob.getDirection());
//0
System.out.println(bob.getGrid());
/*{(1, 5)=BoxBug[location=(1, 5),direction=0,color=java.awt.Color[r=255,g=0,b=0]]}*/
System.out.println(bob.getLocation());
//(1,5)

49. BAD, BAD, BAD!
Don't do this!
Don't place Actors using the grid's put method
ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
Bug bob = new BoxBug(3);
world.add(new Location(1,5), bob);
bob.removeSelfFromGrid();
theGrid.put(new Location(2,6),bob);
System.out.println(bob.getLocation());
//Displays null!

50. Moving Actiors This is ok! ActorWorld world = new ActorWorld();
Grid theGrid = world.getGrid();
Bug bob = new BoxBug(3);
world.add(new Location(1,5), bob);
bob.moveTo(new Location(2,6));
System.out.println(
bob.getLocation());
//Displays (2,6)

51. p 23, Do you know? Name three properties of every actor.
When an actor is constructed, what is its direction and color?

52. The Bug class Bugs (like Rocks and Flowers) extend the Actor class
ActorWorld world = new ActorWorld();
Object bob = new BoxBug(3);
System.out.println(bob instanceof Bug);
System.out.println(bob instanceof Actor);
System.out.println(bob instanceof Rock);
instanceof gives true if the Object is an instance of that class

53. The inheritance hierarchy
Actor
Bug
Flower
Rock
BoxBug

54. Jumper project
Group project at end of Chapter 3--Feel free to choose some partners, or work on it yourself
Jumpers move 2 spaces and jump over other Actors that are in the way
You'll need a JumperRunner and Jumper class
Put them in a Jumper folder in the projects
No one correct way, your Jumper may behave differently than another groups

55. canMove() public boolean canMove() { Grid<Actor> gr = getGrid();
if (gr == null)
return false;
Location loc = getLocation();
Location next =
loc.getAdjacentLocation(getDirection());
if (!gr.isValid(next))
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 }

56. What's the output? ActorWorld world = new ActorWorld();
Bug bob = new BoxBug(3);
world.add(new Location(2,2), bob);
bob.removeSelfFromGrid();
System.out.println(bob.getGrid());

57. canMove() if (gr == null) return false; public boolean canMove() {
Grid<Actor> gr = getGrid();
if (gr == null)
return false;
Location loc = getLocation();
Location next =
loc.getAdjacentLocation(getDirection());
if (!gr.isValid(next))
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 }

58. canMove() Location next = loc.getAdjacentLocation(getDirection());
public boolean canMove() {
Grid<Actor> gr = getGrid();
if (gr == null)
return false;
Location loc = getLocation();
Location next = loc.getAdjacentLocation(getDirection());
if (!gr.isValid(next))
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 }

59. canMove() Actor neighbor = gr.get(next); return (neighbor == null) ||
public boolean canMove() {
Grid<Actor> gr = getGrid();
if (gr == null)
return false;
Location loc = getLocation();
Location next =
loc.getAdjacentLocation(getDirection());
if (!gr.isValid(next))
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 }

60. move() from Bug public void move() { Grid<Actor> 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); }

61. What is the output? Object bob = new Flower(); System.out.println(
bob instanceof Flower);
System.out.println(bob instanceof Rock);
System.out.println(bob instanceof Bug);
bob instanceof Actor);
bob instanceof Object);

62. Jumper import statements
My Jumper class had the following imports:
import info.gridworld.actor.*;
import info.gridworld.grid.*;
My JumperRunner class used:
import info.gridworld.grid.Location;

63. Chapter 4 Critters process a list of other actors and then move
getActors() gets a list of all the neighboring actors (max 8)
Bugs don't pay attention to other actors, they just check to see if the location they want to move to is available

64. CritterRunner public class CritterRunner {
public static void main(String[] args)
ActorWorld world = new ActorWorld();
world.add(new Location(7, 8), new Rock());
world.add(new Location(3, 3), new Rock());
world.add(new Location(2, 8),
new Flower(Color.BLUE));
world.add(new Location(5, 5),
new Flower(Color.PINK));
world.add(new Location(1, 5),
new Flower(Color.RED));
world.add(new Location(7, 2),
new Flower(Color.YELLOW));
world.add(new Location(4, 4), new Critter());
world.add(new Location(5, 8), new Critter());
world.show(); }

65. Any guesses what the Critter will do?

66. What happened?

67. Critter public class Critter extends Actor { /**
* A critter acts by getting a list of other actors, processing that list,
* getting locations to move to, selecting one of them, and moving to the
* selected location. */
public void act()
if (getGrid() == null)
return;
ArrayList<Actor> actors = getActors();
processActors(actors);
ArrayList<Location> moveLocs =
getMoveLocations();
Location loc = selectMoveLocation(moveLocs);
makeMove(loc); }

68. How does a Critter "process" it's neighbors?
public void processActors(ArrayList<Actor> actors) {
for (Actor a : actors)
if (!(a instanceof Rock) &&
!(a instanceof Critter))
a.removeSelfFromGrid(); }

69. How does a Critter decide which location to move to?
public ArrayList<Location> getMoveLocations() {
return getGrid().
getEmptyAdjacentLocations(getLocation()); }
public Location selectMoveLocation(
ArrayList<Location> locs)
int n = locs.size();
if (n == 0)
return getLocation();
int r = (int) (Math.random() * n);
return locs.get(r);

70. How does a Critter decide which location to move to?
public void makeMove(Location loc) {
if (loc == null)
removeSelfFromGrid();
else
moveTo(loc); }

71. Any guesses what the Critter will do?

72. What happened?

73. What's going to happen?

74. Which actor moved first?

75. Practice Quiz Question
How many objects will be removed after one step?
Right click on this slide and choose Pointers Options | Ballpoint pen. Draw a possible resulting arrangement. X out any actors that are moved or removed.

76. Chameleon Critters
What do you think the Chameleon will do?

77. Chameleon Critters
What do you think the Chameleon will do?

78. Chameleon Critters
Critters process a list of other actors and then move
Chameleons process a list of neighbors by randomly choosing a neighbor and assuming its color
Then they move

79. Chameleon Critters public void processActors(
ArrayList<Actor> actors) {
int n = actors.size();
if (n == 0)
return;
int r = (int) (Math.random() * n);
Actor other = actors.get(r);
setColor(other.getColor()); }

80. Practice Quiz Questions
What is the probability that the Chameleon will be red after it acts?
that it will be blue after it acts?

81. The red critter is a chameleon
Look carefully for a difference in the way a chameleon moves compared to a "normal" critter

82. The red critter is a chameleon
Look carefully for a difference in the way a chameleon moves compared to a "normal" critter

83. super classes and sub classes
class ChameleonCritter
extends Critter
Critter is the super class
ChameleonCritter is the sub class
the sub class extends the super class

84. super //from ChameleonCritter.class public void makeMove(Location loc){
setDirection(
getLocation().getDirectionToward(loc));
super.makeMove(loc); }

85. super() Super has two meanings:
With parenthesis, it calls the super class constructor (e.g. super() )
With a dot, it calls the member methods of the super class (e.g. super.makeMove(loc) )

86. What is the output? public class SuperDemo extends Applet {
public void init() {
SuperClass bob = new SuperClass(5);
SubClass sue = new SubClass();
System.out.println(bob.myInt);
System.out.println(sue.myInt);
System.out.println(sue.mySecondInt); }
class SuperClass{
int myInt;
SuperClass(int nInt){
System.out.println("Building a Super");
myInt = nInt;
class SubClass extends SuperClass{
int mySecondInt;
SubClass(){
super(3);
System.out.println("Building a Sub");
mySecondInt = 4;

87. What's wrong with SubClass b = new SubClass(3);? class SuperClass{
int myInt;
SuperClass(int nInt){
myInt = nInt; }
class SubClass extends SuperClass{
int mySecondInt;
SubClass(){
super(3);
mySecondInt = 4;

88. Construtors are NEVER inherited
Construtors are NEVER inherited. To call a constructor of the super class you have to call super on the first line of the sub class constructor
class SuperClass{
int myInt;
SuperClass(int nInt){
myInt = nInt; }
class SubClass extends SuperClass{
int mySecondInt;
SubClass(){
super(3);
mySecondInt = 4;

89. More on super()
Every time a new instance of a sub class is created, we start by building a super
class SeaHorse extends Fish{…}
SeaHorse Bob = new SeaHorse();

90. More on super()
On the very first line of the SeaHorse constructor, there is an "invisible" call to super();
class SeaHorse extends Fish{
public SeaHorse(){
super(); //invisible
//lots more java }

91. More on super() The call is to the default, no argument constructor
If we want to call a different version of the constructor, one with arguments, we need to do it on the very first line of the constructor
class SeaHorse extends Fish{
public SeaHorse(){
super(??,??); }

92. What happens if a sub class doesn’t have a constructor?
Does it inherit the constructor from the super class?
For instance, look at the code for the ChameleonCritter—there's no constructor!

93. What happens if a sub class doesn’t have a constructor?
Does it inherit the constructor from the super class?
NO NO NO!
Java generates an "invisible" constructor that calls super()
class ChameleonCritter
extends Critter{
public Critter(){ //invisible
super(); }
//lots more Java

94. Buidling new Critters Five methods that may need to be overwritten:
getActors();
processActors();
getMoveLocations();
selectMoveLocations();
makeMove();

95. CrabCritters
When Crab critters look for something to eat, they don't look at all the neighbors, just the ones in front (front, right-front and left front)
What needs to overwritten getActors() or processActors()?

96. How does a Critter "process" it's neighbors?
public void processActors(ArrayList<Actor> actors) {
for (Actor a : actors)
if (!(a instanceof Rock) &&
!(a instanceof Critter))
a.removeSelfFromGrid(); }

97. How does a Critter get a list of it's neighbors?
public ArrayList<Actor> getActors() {
return
getGrid().getNeighbors(getLocation()); }

98. Since a Critter and Crab both process the neighbors by eating them, the only difference is the list. getActors() needs to be changed, not processActors()
public ArrayList<Actor> getActors() {
ArrayList<Actor> actors = new ArrayList<Actor>();
int[] dirs =
{ Location.AHEAD, Location.HALF_LEFT,
Location.HALF_RIGHT };
for (Location loc : getLocationsInDirections(dirs))
Actor a = getGrid().get(loc);
if (a != null)
actors.add(a); }
return actors;

99. Moving Critters
Crab Critters move differently: A CrabCritter can move only to the right or to the left. If both are open, it chooses randomly. (if it can't move it turns 90 degrees)
What needs to be overwritten?
getMoveLocations();
selectMoveLocations();
makeMove();

100. Moving Critters
Since Critters choose locations randomly, only 1 and 3 need to be changed
getMoveLocations();
selectMoveLocations();
makeMove();

101. Image Information
You can create an image for any class you create in GridWorld. The image must have the exact same name as the class. Case matters!
public class RockHound
.....
RockHound.gif
IMPORTANT: Save the image in the same folder as the class file, not the java file!

102. Image Information
The class files for my projects are in the GridWorldCode folder in my JCreator Projects folder (yours is probably Z:\Java\GridWorldCode)

103. Image Information The picture will load automatically
GridWorld will "tint" the picture depending on the actors color
setcolor(null) will prevent the image from being tinted

104. What is the output of this program?
public class ThisDemo {
public static void main(String[] args) {
WhatsIt first = new WhatsIt();
WhatsIt second = new WhatsIt();
first.combine(second);
System.out.println(first.getNum()); }
class WhatsIt{
private int myNum;
public WhatsIt(){myNum = 4;}
public int getNum(){return myNum;}
public void combine(WhatsIt one){
myNum = myNum + one.myNum;

105. What is the output of this program?
public class ThisDemo {
public static void main(String[] args) {
WhatsIt first = new WhatsIt();
WhatsIt second = new WhatsIt();
first.combine(second);
System.out.println(first.getNum()); }
class WhatsIt{
private int myNum;
public WhatsIt(){myNum = 4;}
public int getNum(){return myNum;}
public void combine(WhatsIt one){
myNum = myNum + one.myNum;

106. Problem: Write a new WhatsIt member method called doubleIt
Problem: Write a new WhatsIt member method called doubleIt. doubleIt combines a WhatsIt with itself
WhatsIt first = new WhatsIt();
first.doubleIt();
System.out.println(first.getNum()); //8
class WhatsIt{
private int myNum;
public WhatsIt(){myNum = 4;}
public int getNum(){return myNum;}
public void combine(WhatsIt one){
myNum = myNum + one.myNum; }
public void doubleIt(){
combine(???);

107. Problem: Can we use first as the argument?
WhatsIt first = new WhatsIt();
first.doubleIt();
System.out.println(first.getNum()); //8
class WhatsIt{
private int myNum;
public WhatsIt(){myNum = 4;}
public int getNum(){return myNum;}
public void combine(WhatsIt one){
myNum = myNum + one.myNum; }
public void doubleIt(){
combine(first); //doesn't work

108. the keyword this means "the object in front of the dot".
WhatsIt first = new WhatsIt();
first.doubleIt();
System.out.println(first.getNum()); //8
class WhatsIt{
private int myNum;
public WhatsIt(){myNum = 4;}
public int getNum(){return myNum;}
public void combine(WhatsIt one){
myNum = myNum + one.myNum; }
public void doubleIt(){
combine(this); //Now it works!

109. this is a reference to the object that called the method
think: the object in front of the dot

110. this The scope of bob is shown in yellow
We can't use bob in the Thingy class
public class ThisDemo extends Applet {
private Thingy bob
public void init() {
bob = new Thingy(); }
public void paint(Graphics g) {
bob.display();
class Thingy{
private int myNum;
public Thingy(){myNum = 3;}
public void display(){
System.out.println(bob.myNum);
//doesn't work

111. this
myNum by itself means "the myNum that belongs to the object that called the method"
public class ThisDemo extends Applet {
private Thingy bob
public void init() {
bob = new Thingy(); }
public void paint(Graphics g) {
bob.display();
class Thingy{
private int myNum;
public Thingy(){myNum = 3;}
public void display(){
System.out.println(myNum); //OK

112. this this.myNum means the same as just myNum
public class ThisDemo extends Applet {
private Thingy bob
public void init() {
bob = new Thingy(); }
public void paint(Graphics g) {
bob.display();
class Thingy{
private int myNum;
public Thingy(){myNum = 3;}
public void display(){
System.out.println(this.myNum); //OK

113. this
You may use this anywhere you want to refer to the object in front of the dot
There is only one situation where you have to use this: When you want to pass the object in front of the dot as an argument
Good Style: Don't use this unless you need to

114. What is the output of this program?
public class ThisDemo {
public static void main(String[] args) {
TryIt first = new TryIt("hello");
TryIt second = new TryIt("world");
second.modify(first);
System.out.println(second.getName());
first.mystery();
System.out.println(first.getName());} }
class TryIt{
private String myName;
public TryIt(String sName){myName = sName;}
public String getName(){return myName;}
public void modify(TryIt one){
myName = one.myName + "-" + myName;
public void mystery(){modify(this);}

115. When making new Actors
The following import statements seem to give you everything you could possibly need
import info.gridworld.actor.*;
import info.gridworld.grid.*;
import java.awt.Color;
import java.util.ArrayList;
Make sure that you make a new folder for your new Actor class and a new Runner class as well
Make sure the runner is putting instances of your new Actor class into the world!

116. BlusterCritter Has a new private int c for courage
Counts all the Critters within 2 steps:
If number of critters< c, color brightens
If number of critters>= c, color darkens

117. BlusterCritter Has a new private int c for courage
Counts all the Critters within 2 steps:
If number of critters< c, color brightens
If number of critters>= c, color darkens
Which methods need to be overwritten?
getActors();
processActors();
getMoveLocations();
selectMoveLocations();
makeMove();

118. BlusterCritter getActors();
will get a list of all the Critters within 2 steps
processActors();
will check the size of the list and lighten or darken accordingly

119. BlusterCritter public ArrayList<Actor>getActors() {
ArrayList <Actor> theList =
new ArrayList<Actor>(); ??
return theList; }
We need to check 24 locations
5x5 = 25 minus the one location
the BlusterCritter is in

120. BlusterCritter for(int nRow=-2;nRow<=2;nRow++)
public ArrayList<Actor>getActors() {
ArrayList <Actor> theList =
new ArrayList<Actor>();
for(int nRow=-2;nRow<=2;nRow++)
for(int nCol=-2;nCol<=2;nCol++)
//check all 25 }
//remove ourself
return theList;

121. How could I remove the BlusterCritter from the list?
public ArrayList<Actor>getActors() {
ArrayList <Actor> theList =
new ArrayList<Actor>();
for(int nRow=-2;nRow<=2;nRow++)
for(int nCol=-2;nCol<=2;nCol++) ?? }
theList.remove( ?? );
return theList;

122. Brightening can make an Exception
red = (int) (c.getRed() + 5);
green = (int) (c.getGreen() +5);
blue = (int) (c.getBlue() +5); ??
setColor(new Color(red, green, blue));

123. QuickCrab
moves two spaces if possible, otherwise moves as a "normal" Crab
What should be overwritten?
getActors();
processActors();
getMoveLocations();
selectMoveLocations();
makeMove();

124. QuickCrab getMoveLocations();
moves two spaces if possible, otherwise moves as a "normal" Crab
What should be overwritten?
getActors();
processActors();
getMoveLocations();
selectMoveLocations();
makeMove();

125. getMoveLocations() ArrayList<Location> locs =
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
???
return locs; }

126. getMoveLocations() //Find the location one to the left
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//Find the location one to the left
return locs; }

127. getMoveLocations() //Find the location one to the left
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//Find the location one to the left
//Find the location two to the left
return locs; }

128. getMoveLocations() //Find the location one to the left
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//Find the location one to the left
//Find the location two to the left
//if they are both valid and unoccupied, add two to the left to the list
return locs; }

129. getMoveLocations() //Find the location one to the left
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//Find the location one to the left
Location oneLeft = ???
return locs; }

130. getMoveLocations() ???.getAdjacentLocation(???);
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//Find the location one to the left
Location oneLeft =
???.getAdjacentLocation(???);
return locs; }

131. getMoveLocations() getLocation().getAdjacentLocation(???);
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//Find the location one to the left
Location oneLeft =
getLocation().getAdjacentLocation(???);
return locs; }

132. getMoveLocations() getLocation().getAdjacentLocation(
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//Find the location one to the left
Location oneLeft =
getLocation().getAdjacentLocation(
getDirection() + Location.LEFT);
return locs; }

133. What if two to the left and two to the right are both unavailable?
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//lots of java
if(locs.size == 0)
???
else
return locs; }

134. What if two to the left and two to the right are both unavailable?
public ArrayList<Location> getMoveLocations() {
ArrayList<Location> locs =
new ArrayList<Location>();
//lots of java
if(locs.size == 0)
return /* normal crab locations */
else
return locs; }

135. KingCrab when processing actors, it moves them "one away"
If they can't move "one away" they are removed

136. KingCrab when processing actors, it moves them "one away"
If they can't move "one away" they are removed
What should be overwritten?
getActors();
processActors();
getMoveLocations();
selectMoveLocations();
makeMove();

137. public class superWhatOutput{
public static void main(String args[])
Thingy[] aBunch = new Thingy[5];
for(int nI = 0; nI < aBunch.length; nI++)
if(nI % 2 == 0)
aBunch[nI] = new Thingy(nI);
else
aBunch[nI] = new Widget(nI,'x');
aBunch[nI].write(); }
class Thingy
private int myNum;
public Thingy(int nNum){myNum = nNum;}
public int getNum(){return myNum;}
public String toString()
if(myNum%3 == 0)
return "three";
return "no";
public void write()
System.out.println(this);
class Widget extends Thingy {
private char myLetter;
public Widget(int nNum, char cLetter)
super(nNum);
myLetter = cLetter; }
public String toString()
return myLetter + super.toString();

138. aBunch 1x 2 3x 4
index 1 2 3 4

139. for(int nI = 0; nI < aBunch.length; nI++)
aBunch[nI].write();
aBunch 1x 2 3x 4
index 1 2 3 4

140. for(int nI = 0; nI < aBunch.length; nI++)
aBunch[nI].write();
public void write() {
System.out.println(this); }
aBunch 1x 2 3x 4
index 1 2 3 4

141. for(int nI = 0; nI < aBunch.length; nI++)
aBunch[nI].write();
public void write() {
System.out.println(this); }
public String toString() //thingy
if(myNum%3 == 0)
return "three";
else
return "no";
public String toString() //widget
return myLetter + super.toString();
aBunch 1x 2 3x 4
index 1 2 3 4