1. Games and Simulations O-O Programming in Java The Walker School
Newton’s Lab
Games and Simulations
O-O Programming in Java
The Walker School
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2. Space, The Final Frontier
You can create new bodies.
What kinds of bodies are in our solar system? Why don’t we see a class for each type?
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3. Solar System
The main types of bodies in our solar system contains planets, planetoids, moons, asteroids and comets. While each of these varies in size, mass, composition and velocity, they are also similar in many ways. Because each object does have a size, mass, and velocity, we can use abstraction in programming to create a Body Class that handles each of these items as variables.
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4. 3 Basic Methods Right-click on Space world at the top?
What happens when you activate one of these methods?
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5. Public Methods
Right – click on a body. What public methods does it have?
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6. Inspecting Planet Properties
Right click on a planet and inspect its properties. What is the mass?
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7. Space Public Methods What do the numbers mean in each case?
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8. Helper Classes
Also known as Abstract classes. They do not have constructors, so you can’t create instances of them.
2 Support Classes
SmoothMover
Vector
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9. Helper (or Support) Classes http://www. greenfoot
Some Helper Classes
Counter
Explosion
Mover
Plotter
Rotator
Slider
Vector
Wander
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10. Classes Inherited from SmoothMover
How are these 2 classes different?
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What classes are inherited from Vector? Why is it not under Actor?

11. Overloading
Can have the same name, as long as their parameters are different. This means that the methods (or constructors) have different signatures.
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Has 2 constructers “Body” with different parameters.

12. Vectors dy dx Polar Representation = length and direction
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Polar Representation = length and direction
Cartesian Representation = dx and dy

13. Vector Class Variables
Open SmoothMover and Vector. What methods do they have?
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14. Method Inheritance
Open SmoothMover and Vector. Which methods can you call from the object menu?
Which can’t you call?
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15. Default Constructors
Does not have any parameters. Makes it easy to create bodies interactively without having to specify details. This is a default constructor.
Is this an example of overloading?
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16. this.
Only possible in constructors. Used to execute another constructor.
What happens when you remove this. in front of the word mass? Does it compile?
We’ll find out in Lab6 !
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17. Constants Means the value never changes.
Means it’s shared between all actors of this class.
These variables are constants. These variables do not change in a program.
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18. Add Movement
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19. Body Behavior Create multiple bodies. How do they behave?
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20. Add Movement (Left) How would you make the body move left?
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21. Solution: Left Movement
Change the + to a -
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22. Java Packages import java.awt.Color;
Programmers typically use packages to organize classes belonging to the same category or providing similar functionality.
import java.awt.Color;
Imported using dot notation.
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23. Importing Java Color Library
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24. Default Color of Body Sets the RBG values Calls the Color class.
What is the legal range for colors?
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25. Adding Gravitational Force
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26. Movement
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27. Apply Force To Do List
Apply forces from other bodies: get all other bodies in space; for each of those bodies { apply gravity from that body to our own; }
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28. Apply Force – Part I
Methods only intended to be called from within the class can be labeled private. When methods are intended to be called from outside the class, they should be labeled public.
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29. Greenfoot World Methods
Which methods give us access to objects within the world?
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30. Getting Objects Java.util.List getObjects(java.lang.Class cls)
Gives a list of all objects in the world of a particular class.
getObjects(Body.class)
Calls the objects in the world.
getObjects(null)
Keyword null is a special expression that means nothing, or no object.
getWorld().getObjects(Body.class)
Can be used from an actor to get all objects of class Body.
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31. Java.util.list What methods can be used to add items to a list?
What methods can be used to remove items to a list?
What methods can be used to found out how many items are in a list?
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32. Lists are not Classes, but Interfaces
generic type – need to put the type of list in the brackets, such as String.
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33. Apply Force – Part II
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34. For (every) Loops for (ElementType variable : collection) {
Helps to step through the items in a collection, or list.
for (ElementType variable : collection) {
statements; }
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35. Apply Force – Part III Refers to the current object.
Use an if-statement so that gravity is applied to all objects (bodies) in the list except the current object.
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36. Applying Gravity
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37. Newton’s Law
Newton's Law of Universal Gravitation states that every massive particle in the universe attracts every other massive particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
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38. Apply Gravity To Do List
Why do these numbers need to be doubles?
Apply gravity from an object { get the location of the objects in space; calculate the distance between each of the objects; create a new vector using this data to determine direction; calculate the distance between the two bodies using the Pythagoras theorem; use Newton's formula to calculate the strength of the force calculate the acceleration; add the force; }
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39. Pythagorean Theorem
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Look up the class Math in the Java API. How many parameters does the sqrt method have? (see answer on the next slide)

40. Square Root
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Now, find the method that can be used to find the maximum of two integers. What is it called?

41. Acceleration Acceleration = Force / Mass
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42. Appling Gravity Method
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43. Trying it Out
Try out the three initializing methods from Space object again. What do you observe?
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44. Experimenting with Gravity
Change the gravity constant at the top of the body class. What happens?
Change it by ½, change it by doubling it; change it by 1, change it by a decimal.
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45. Experimenting with Mass & Movement
Experiment with changes to the mass and/or initial movement of the bodies defined in the Body class. What happens?
size
mass
vector
movement r g b x y
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When experimenting it’s important to change one variable at a time.

46. Programming / Research Challenge
Create some new set-ups of stars and planets and see how they interact. Can you come up with a system that is stable? With what you have programmed, could you create a model of our solar system? Is our solar systems stable? Explain your reasoning.
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47. Obstacles, Gravity and Music
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48. Improvements to Lab v. 3 Improvements new Obstacle class
modified Body class
increased Gravity
fixed obstacles
more planets
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49. Add Obstacle Class Directions Right click on Actor Add new subClass
Name it “Obstacle”
Choose the orange block from “Objects”
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50. Create Class Stub
What are the basic methods we need to add to our stub?
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51. Create a Constructor
What parameters do we want to pass into the constructor?
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52. Add Parameters to Constructor
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We want to know when a body hits the obstacle.
When it does we want to play a sound.

53. Add Play Sound Method
Use Audacity to create a sound that you want to play when the planet hits the obstacle.
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What folder in the project, does this sound go?

54. Add an Act Method Stub
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55. Adding Obstacles What type of data structure is this?
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56. Act To Do List
public void act { call the intersecting object method from Actor use a conditional statement to determine if the object has collided with the obstacle if touched, set the appropriate image play sound if not touched, }
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57. Functioning Act Method
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58. Increase the Gravity Constant
Gravity has been added to make the “bodies” move faster. What functionality has been added to slow them down?
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59. Slowing Fast Bodies
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60. Create Random Bodies Stub
What parameter(s) do we want to pass in order to create a number of bodies?
Don’t forget to call this method in the act method.
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61. Random Bodies To Do List
write a method stub{ create a loop make a body of random size make a body of random mass (size * #?) give the body a random direction give the body a random speed give the body a random location (within the world) give the body a random color (r, g, b) create a new instance of the body (pass the parameters) }
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62. Create Random Bodies Method
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63. Bouncing Bodies To Do List
write a method stub{ get the body’s location determine if the body is at the edge of the world cast the location to decimals (for movement) change the direction of movement, either in vertical or horizontal plane decelerate the body }
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64. Reflecting Bodies at World Edge
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Don’t forget to add the bounceAtEdge() method call in act() method.

65. Activities – Part I
Change the number of bodies that are created by default in this scenario.
Create a different arrangement of obstacles in your scenario.
Use different sounds (sound files) for your obstacles.
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66. Changing the Number of Bodies
Under Space class change the number of random bodies created.
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67. Different Obstacle Arrangement
Creates a random location along they y-axis.
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68. Fixed Obstacle Arrangement
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69. Different Sounds
Changes the set of sounds from piano to trumpet sounds. These 1-minute notes were recorded by band members in Audacity then stored in the project’s sound folder. We added the prefix of “tp” so we didn’t have to change any of the names in the soundFiles [] list.
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70. Activities – Part II Use different images for your obstacles.
Make planets change color every time the bounce off the edge of the universe.
Make planets change color every time they hit an obstacle.
Make a different kind of obstacle that gets switched on and off by being hit. When on, it continuously blinks and produces a sound at fixed intervals.
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71. Change the Obstacle Image
Directions
Right-click on Obstacle class
Choose Set-Image
Choose the new image from the Greenfoot image library.
Make your own image in Photoshop and add it to the image folder for the project.
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72. Programming Challenge
Comets and asteroids move through the solar system. Create an image for one of these using Photoshop and add it to the world as an obstacle. To increase the difficulty of the challenge, have the object appear periodically at different speeds and if a ball hits this object, have it make a special sound.
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73. Activities – Part III
Add some keyboard control. For example, pressing the right arrow key could add a small force to the right to all Body objects.
Allow adding more planets. A mouse click into the universe while it is running should create a new planet at that location.
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