Crab World

1. Crab World Games and Simulations O-O Programming in Java The Walker School The Walker School – Games and Simulations - 2010

2. 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

3. 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

4. Movement Method Call The Walker School – Games and Simulations - 2010

5. Turning Parameter What happens to the crab if you use a negative number? The Walker School – Games and Simulations - 2010

6. Standard Java Class Import (Library) Statements Class Signature Instance Variables (not shown) Constructors (not shown) Method Signature The Walker School – Games and Simulations - 2010

7. 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

8. 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

9. 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

10. Dealing with Screen Edges Conditional Statement The Walker School – Games and Simulations - 2010

11. Conditionals are Decision Statements Are if … then statements Condition Only executed if something is True. Instruction(s) The Walker School – Games and Simulations - 2010

12. Conditional Types …gives use the ability to check conditions and change the behavior of the program accordingly • Branched • Chained • Nested if (method()) statement; statement;

13. Watch – Making Things Move (Part I)http://www.youtube.com/watch?v=KUwt0K4K4_o The Walker School – Games and Simulations - 2010

14. API Views Documentation View Source Code View Contains Class Tree Author Constructors Methods The Walker School – Games and Simulations - 2010

15. Adding Random Behavior What percentage of time will the crab turn 5 degrees? Operator The Walker School – Games and Simulations - 2010

16. 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

17. Common Operators • + • - • * • > • < • <= or >= • == • != • || • & • % What do each of these operators do? The Walker School – Games and Simulations - 2010

18. 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

19. 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

20. Explain the behavior being expressed here. The Walker School – Games and Simulations - 2010

21. Adding a New Subclass 1. Name the world. 2. Choose a new object. 1. Right click on class. 2. Choose new subclass. The Walker School – Games and Simulations - 2010

22. 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

23. Class Diagram Relationships What do crabs eat? or What eats a crab? A “crab” is-a “animal” The Walker School – Games and Simulations - 2010

24. 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

25. 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

26. 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

27. One Possible Solution Remember to call the method in the act() method. The Walker School – Games and Simulations - 2010

28. Adding Keyboard Control static booleanisKeyDown(String key) Method Call Class Method Returns Either T or F Expects a String Any Key The Walker School – Games and Simulations - 2010

29. 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

30. One Possible Solution The Walker School – Games and Simulations - 2010

31. 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

32. 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

33. Ending the Game In what class is this method called? The Walker School – Games and Simulations - 2010

34. 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

35. Java Keywordshttp://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

36. 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

37. Parameter List Allows us to pass information to the constructor. The Walker School – Games and Simulations - 2010

38. 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

39. 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

40. 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

41. One Possible Solution The Walker School – Games and Simulations - 2010

42. Adding a Win-State(counting worms) The Walker School – Games and Simulations - 2010

43. 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

44. 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

45. Increment the Count – Step #3 The Walker School – Games and Simulations - 2010

46. Crab Win-State, Play Winner The Walker School – Games and Simulations - 2010

47. 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

48. 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

49. One Possible Solution The Walker School – Games and Simulations - 2010

50. Adding a Second Player The Walker School – Games and Simulations - 2010