Crab World Games and Simulations O-O Programming in Java The Walker School The Walker School – Games and Simulations - 2010 Crab World Have students play the working game for a few minutes. What are the objects in this world? What are the classes in this world? The Walker School – Games and Simulations - 2010 Object Oriented Programming The discipline of object-oriented programming is based on methods, subroutines that are attached to objects or object classes. In the compilation technique called threaded code, the executable program is basically a sequence of subroutine calls. The Walker School – Games and Simulations - 2010 Movement Method Call The Walker School – Games and Simulations - 2010 Turning Parameter What happens to the crab if you use a negative number? The Walker School – Games and Simulations - 2010 Standard Java Class Import (Library) Statements Class Signature Instance Variables (not shown) Constructors (not shown) Method Signature The Walker School – Games and Simulations - 2010 Functions and Methods A function is a named sequence of statements that performs a desired operation. This operation is specified in a function definition. NAME( LIST OF PARAMETERS ): STATEMENTS There can be any number of statements inside the function, but they have to be indented from the left margin. Creating a new function gives you an opportunity to name a group of statements. Functions can simplify a program by hiding a complex computation behind a single command and by using English words in place of arcane code. Creating a new function can make a program smaller by eliminating repetitive code. The Walker School – Games and Simulations - 2010 Method Call This conditional statement uses a built in function to turn an object if it hits the edge of the world. Method Body Method Call The Walker School – Games and Simulations - 2010 Function (or Method) Call The value or variable, which is called the argument of the function, has to be enclosed in parentheses. It is common to say that a function “takes” an argument and “returns” a result. The result is called the return value. turn (speed); The Walker School – Games and Simulations - 2010 Dealing with Screen Edges Conditional Statement The Walker School – Games and Simulations - 2010 Conditionals are Decision Statements Are if … then statements Condition Only executed if something is True. Instruction(s) The Walker School – Games and Simulations - 2010 Conditional Types • Branched • Chained • Nested …gives use the ability to check conditions and change the behavior of the program accordingly if (method()) { statement; statement; } Watch – Making Things Move (Part I) http://www.youtube.com/watch?v=KUwt0K4K4_o The Walker School – Games and Simulations - 2010 API Views Source Code View Documentation View Contains 1. Class Tree 2. Author 3. Constructors 4. Methods The Walker School – Games and Simulations - 2010 Adding Random Behavior What percentage of time will the crab turn 5 degrees? Operator The Walker School – Games and Simulations - 2010 Operators Operators are special symbols that represent computations like addition and multiplication. The values the operator uses are called operands. Assignment (=) Comparison (==, <=, >=, !=, etc.) Logical: &&, ||, ! (and, or, not) When more than one operator appears in an expression, the order of evaluation depends on the rules of precedence. The Walker School – Games and Simulations - 2010 Common Operators • • • • • • + * > < <= or >= • • • • • == != || && % What do each of these operators do? The Walker School – Games and Simulations - 2010 Order of Operation The order of evaluation depends on the rules of precedence. PEMDAS Parentheses ( ) Exponentiation Multiplication and Division Operators with the same precedence are evaluated from left to right. The acronym PEMDAS is a useful way to remember the order of operations The Walker School – Games and Simulations - 2010 Dot Notation Used when calling a method defined in another class. Dot Notation Class-name.method-name (parameters); The Walker School – Games and Simulations - 2010 Explain the behavior being expressed here. The Walker School – Games and Simulations - 2010 Adding a New Subclass 1. Right click on class. 2. Choose new subclass. 1. Name the world. 2. Choose a new object. The Walker School – Games and Simulations - 2010 Inheritance Subclass The Crab class inherits all of the methods of the Animal class, while the Animal Class inherits all of the methods of the Greenfoot Actor class. The Walker School – Games and Simulations - 2010 Class Diagram Relationships What do crabs eat? or What eats a crab? A “crab” is-a “animal” The Walker School – Games and Simulations - 2010 Creating New Methods Find this behavior in the Java API? Comments Method Statement Imports the behavior from the java.lang.Class to the Worm class. New methods need to be called in the act() method. The Walker School – Games and Simulations - 2010 Commenting New Methods Comments Each time you add a new method, you should include a comment explaining what it does. Your comments should be clear and concise, free of spelling and grammatical errors. Think of yourself having to read another programmers code. Would you want it to be easy to read? The Walker School – Games and Simulations - 2010 Programming Challenge • Add a new actor to your program, say a lobster or a human that might eat the crab. You will need to copy the act method from the crab to the lobster, and other methods, such as lookForWorm(), which you will need to change to lookForCrab(). The Walker School – Games and Simulations - 2010 One Possible Solution Remember to call the method in the act() method. The Walker School – Games and Simulations - 2010 Adding Keyboard Control static boolean isKeyDown(String key) Method Call Class Method Returns Either T or F Expects a String The Walker School – Games and Simulations - 2010 Any Key Programming Challenge • Add additional keyboard controls to make the crab move up or down. What other keyboard functionality could you add? For example, you could make the crab jump back 10 pixels when it encounters a lobster if you hit the “j” key. The Walker School – Games and Simulations - 2010 One Possible Solution The Walker School – Games and Simulations - 2010 Adding Sound Challenge: Search the internet for other sound files and add a new sound to the Crab class when it east a worm. The Walker School – Games and Simulations - 2010 Watch – Making Things Move (Part II) http://www.youtube.com/watch?v=QWruHXIPDIk&feature=related Mover “Helper” Support Class For more advanced students. The Walker School – Games and Simulations - 2010 Ending the Game In what class is this method called? The Walker School – Games and Simulations - 2010 Creating New Objects Java keyword “new” allows us to create new objects of any of the existing classes. The Walker School – Games and Simulations - 2010 Java Keywords http://en.wikipedia.org/wiki/List_of_Java_keywords Search the list; What is one other keyword that we have used already and what does it mean? The Walker School – Games and Simulations - 2010 Constructors • A special kind of method that is always automatically executed whenever an instance of a class is created. • A constructor has no return type (static or void) between the keyword “public” and the name. • The name of the constructor is always the same as the name of the class. The Walker School – Games and Simulations - 2010 Parameter List Allows us to pass information to the constructor. The Walker School – Games and Simulations - 2010 Arguments and Parameters Arguments are values that control how the function does its job. Some functions can take more than one argument. Values that are passed from one function to another get assigned to variables called parameters. The Walker School – Games and Simulations - 2010 Adding Objects Automatically To populate a world automatically add characters to the “World” class. You can add each object individually, or you can create a method that adds actors randomly. The Walker School – Games and Simulations - 2010 Programming Challenge • Combine what you have learned about random behavior and adding new objects to create a method that would add a random number of worms up to 30 and a random number of lobsters up to 3. The Walker School – Games and Simulations - 2010 One Possible Solution The Walker School – Games and Simulations - 2010 Adding a Win-State (counting worms) The Walker School – Games and Simulations - 2010 Instance Variables – Step #1 Create variables to hold the number of worms. An instance variable is memory that belongs to an object. The Walker School – Games and Simulations - 2010 Assignment – Step #2 Create an assignment and initiate the variable to 0 at the beginning of the game. An assignment is a statement that enables us to store something into a variable. It is written with an equal = symbol. The Walker School – Games and Simulations - 2010 Increment the Count – Step #3 The Walker School – Games and Simulations - 2010 Crab Win-State, Play Winner The Walker School – Games and Simulations - 2010 Lobster Win-State, Play Winner Execution always begins at the first statement of the program. Statements are executed one at a time, in order from top to bottom. This is referred to a the Flow of Execution. The Walker School – Games and Simulations - 2010 Programming Challenge • The current state of your games allows a player to win if their crab eats 8 worms. How would you make sure there were at least 8 worms added to each new game, if you were using a random number generator? The Walker School – Games and Simulations - 2010 One Possible Solution The Walker School – Games and Simulations - 2010 Adding a Second Player The Walker School – Games and Simulations - 2010 Programming Challenge • Add a second player where one of you plays the crab and another plays the lobster. Each time the game starts, there will be one crab and one lobster. You will need to add keyboard controls for each character. Make sure the key controls are on opposite sides of the keyboard. The number of worms at the beginning of the game can be random. The Walker School – Games and Simulations - 2010 Crab Keyboard Controls Solution The Walker School – Games and Simulations - 2010 Lobster Keyboard Controls Solution The Walker School – Games and Simulations - 2010 World Population Solution The Walker School – Games and Simulations - 2010 Places to Hide The Walker School – Games and Simulations - 2010 Programming Challenge • Add places for the crab to hide from the lobster, such as a rock or a beach house. Your choices are to add one rock all the time, or to add a random number of rocks. Probably, shouldn’t be more than 3 objects at a time. Also, how would you make sure that there is always at least one object for the crab to hide behind. The Walker School – Games and Simulations - 2010 Add a Rock Adds a rock to the world for the crab to hide behind. The Walker School – Games and Simulations - 2010 Random Number of Rocks Remember to comment out the firstRock object. Otherwise you will get the random number +1 rock. The Walker School – Games and Simulations - 2010 Adding a Penalty The Walker School – Games and Simulations - 2010 Extended Programming Challenge • Create a penalty for the crab and the lobster. If the crab touches the edge of the world, then another worm is added to the world and his score goes down by 1. If the lobster touches the edge of the world, then a point is added to the crab’s score. The Walker School – Games and Simulations - 2010 Adding A Win Message Done after Piano Project The Walker School – Games and Simulations - 2010 Adding a Win Message Step #1: Import the necessary Java libraries. The Walker School – Games and Simulations - 2010 Adding a Win Message (cont.) Step #2: Create the method. The Walker School – Games and Simulations - 2010 Adding a Win Message (cont.) Step #3: Cast the method in the CrabWinState(). The Walker School – Games and Simulations - 2010