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 The Walker School – Games and Simulations - 2010

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? The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

3 Basic Methods Right-click on Space world at the top? What happens when you activate one of these methods? The Walker School – Games and Simulations - 2010

Public Methods Right – click on a body. What public methods does it have? The Walker School – Games and Simulations - 2010

Inspecting Planet Properties Right click on a planet and inspect its properties. What is the mass? The Walker School – Games and Simulations - 2010

Space Public Methods What do the numbers mean in each case? The Walker School – Games and Simulations - 2010

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 The Walker School – Games and Simulations - 2010

Helper (or Support) Classes http://www. greenfoot Some Helper Classes Counter Explosion Mover Plotter Rotator Slider Vector Wander The Walker School – Games and Simulations - 2010

Classes Inherited from SmoothMover How are these 2 classes different? The Walker School – Games and Simulations - 2010 What classes are inherited from Vector? Why is it not under Actor?

Overloading Can have the same name, as long as their parameters are different. This means that the methods (or constructors) have different signatures. The Walker School – Games and Simulations - 2010 Has 2 constructers “Body” with different parameters.

Vectors dy dx Polar Representation = length and direction The Walker School – Games and Simulations - 2010 Polar Representation = length and direction Cartesian Representation = dx and dy

Vector Class Variables Open SmoothMover and Vector. What methods do they have? The Walker School – Games and Simulations - 2010

Method Inheritance Open SmoothMover and Vector. Which methods can you call from the object menu? Which can’t you call? The Walker School – Games and Simulations - 2010

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? The Walker School – Games and Simulations - 2010

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 ! The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

Add Movement The Walker School – Games and Simulations - 2010

Body Behavior Create multiple bodies. How do they behave? The Walker School – Games and Simulations - 2010

Add Movement (Left) How would you make the body move left? The Walker School – Games and Simulations - 2010

Solution: Left Movement Change the + to a - The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

Importing Java Color Library The Walker School – Games and Simulations - 2010

Default Color of Body Sets the RBG values Calls the Color class. What is the legal range for colors? The Walker School – Games and Simulations - 2010

Adding Gravitational Force The Walker School – Games and Simulations - 2010

Movement The Walker School – Games and Simulations - 2010

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; } The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

Greenfoot World Methods Which methods give us access to objects within the world? The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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? The Walker School – Games and Simulations - 2010

Lists are not Classes, but Interfaces generic type – need to put the type of list in the brackets, such as String. The Walker School – Games and Simulations - 2010

Apply Force – Part II The Walker School – Games and Simulations - 2010

For (every) Loops for (ElementType variable : collection) { Helps to step through the items in a collection, or list. for (ElementType variable : collection) { statements; } The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

Applying Gravity The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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; } The Walker School – Games and Simulations - 2010

Pythagorean Theorem The Walker School – Games and Simulations - 2010 Look up the class Math in the Java API. How many parameters does the sqrt method have? (see answer on the next slide)

Square Root The Walker School – Games and Simulations - 2010 Now, find the method that can be used to find the maximum of two integers. What is it called?

Acceleration Acceleration = Force / Mass The Walker School – Games and Simulations - 2010

Appling Gravity Method The Walker School – Games and Simulations - 2010

Trying it Out Try out the three initializing methods from Space object again. What do you observe? The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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 The Walker School – Games and Simulations - 2010 When experimenting it’s important to change one variable at a time.

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. The Walker School – Games and Simulations - 2010

Obstacles, Gravity and Music The Walker School – Games and Simulations - 2010

Improvements to Lab v. 3 Improvements new Obstacle class modified Body class increased Gravity fixed obstacles more planets The Walker School – Games and Simulations - 2010

Add Obstacle Class Directions Right click on Actor Add new subClass Name it “Obstacle” Choose the orange block from “Objects” The Walker School – Games and Simulations - 2010

Create Class Stub What are the basic methods we need to add to our stub? The Walker School – Games and Simulations - 2010

Create a Constructor What parameters do we want to pass into the constructor? The Walker School – Games and Simulations - 2010

Add Parameters to Constructor The Walker School – Games and Simulations - 2010 We want to know when a body hits the obstacle. When it does we want to play a sound.

Add Play Sound Method Use Audacity to create a sound that you want to play when the planet hits the obstacle. The Walker School – Games and Simulations - 2010 What folder in the project, does this sound go?

Add an Act Method Stub The Walker School – Games and Simulations - 2010

Adding Obstacles What type of data structure is this? The Walker School – Games and Simulations - 2010

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, } The Walker School – Games and Simulations - 2010

Functioning Act Method The Walker School – Games and Simulations - 2010

Increase the Gravity Constant Gravity has been added to make the “bodies” move faster. What functionality has been added to slow them down? The Walker School – Games and Simulations - 2010

Slowing Fast Bodies The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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) } The Walker School – Games and Simulations - 2010

Create Random Bodies Method The Walker School – Games and Simulations - 2010

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 } The Walker School – Games and Simulations - 2010

Reflecting Bodies at World Edge The Walker School – Games and Simulations - 2010 Don’t forget to add the bounceAtEdge() method call in act() method.

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. The Walker School – Games and Simulations - 2010

Changing the Number of Bodies Under Space class change the number of random bodies created. The Walker School – Games and Simulations - 2010

Different Obstacle Arrangement Creates a random location along they y-axis. The Walker School – Games and Simulations - 2010

Fixed Obstacle Arrangement The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010

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. The Walker School – Games and Simulations - 2010