1. Games and Simulations O-O Programming in Java The Walker School
Piano
Games and Simulations
O-O Programming in Java
The Walker School
The Walker School – Games and Simulations

2. Piano World What are the Java keywords in this class? Piano Class
Method that specifies the size and resolution of the world
Piano
Constructor

3. Java Key Words
Keywords are words which have a predefined meaning in the language; because of this, programmers cannot use keywords as names for variables, methods, classes, or as any other identifier.
The Walker School – Games and Simulations

4. Animating Keys Key Constructor Key Method
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5. Animated White Key
Switches between two images: white-key and white-key down.
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6. Checking if a Key is Down
Variable that stores “true” while the piano key is down, and “false” while it isn’t.
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7. Producing the Sound Calls the play method. Creates a play method.
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8. Abstraction
A concept or idea not associated with any specific instance. In the case of the piano, we are creating a general Key class that will act the same with each key, i.e. play a sound when a key is pressed.
Thus, we avoid repeating many lines of code.
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9. Step #1 - Create Instance Variables
Create a variable to hold the name of the key.
Create a variable to hold the sound file.
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10. Step #2 - Assignment
Add parameters to the constructor, so that bits of information can be passed in when the object is constructed.
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11. Arguments and Parameters
Arguments are values that control how the function does its job.
Some functions can take more than one argument.
How many parameters can a constructor take?
Values that are passed from one function to another get assigned to variables called parameters.
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12. Programming Challenge
What needs to be added in our play() method to pass a sound from the constructor to the play method which activates a key?
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13. One Possible Solution
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14. Step #3 – Construct Piano
Places a key at the top of the keyboard.
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15. Programming Challenge
Write code to create a second piano key that plays a middle-g (sound file 3g.wav), when the “f” key is pressed. Place the key exactly to the left of the first key.
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16. One Possible Solution
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17. Loops For example: while (condition) { statement; … }
Loops allow you to express commands repeatedly.
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18. Creating Piano Keys w/ Loop
What is the local variable here?
What is the problem here when you run it?
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19. Local Variables Example: int i = 0; while (i < 100) { statement; …
When you create a local variable inside a function, it only exists inside the
function, and you cannot use it outside.
Example:
int i = 0;
while (i < 100) {
statement; …
i = i + 1; }
Also, Local variables are declared inside the function and have no visibility modifier (private or public).
Most common error is to forget to increment the loop counter. If you don’t do it the variable will not change. This would produce an infinite loop.
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20. Programming Challenge
What do you need to do to make sure that the keys are not on top of each other? You will need to figure out how to move each key to a different location on the x access. Each key is 63 pixels wide.
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21. One Possible Solution
You only have to change the x variable in the coordinates, as all of the keys need to be the same distance from the top.
But this causes us another problem. What is it and what’s the solution?
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22. One Possible Solution
Greenfoot refers to the center point of an object, so the first key is placed at x-coordinates 0 and half the key is off the board.
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23. One Big Problem
The problem here is that all of our keys now play middle “g” sound. This is because the are created with a loop and then placed in different positions.
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24. Arrays
Data structures that hold information. It can hold many variables and thus can store many values. Sometimes lists are used, rather than arrays.
Elements in the array can be accessed using an index (the number inside the [ ] brackets).
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25. White-Key Arrays 2D array (list) used for white keys
2D array (list) used for white key notes
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26. Lists [10, 20, 30, 40] (a list of ints)
A list is an ordered set of values, where each value is identified by an index. The values that make up a list are called its elements.
[10, 20, 30, 40] (a list of ints)
["spam", "bungee", "swallow"] (a list of strings)
Lists and strings—and other things that behave like ordered sets—are called sequences.
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A list within another list is said to be nested.

27. White-Key Method w/ While Loop
Execution always begins at the first statement of the program. Statements are executed one at a time, in order from top to bottom.
Creates a local variable “I” and sets it’s initial value to “0”
As long as “i” < the length of our white-key array, do the following…
String concatenation
Create a new white key and associate it with the sound file in the whiteNotes list then append “.wav”
Add the key to a location on the keyboard.
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Count up by 1 each time through the loop…required.

28. Key Method w/ For Loop
What is the structural difference between these 2 loops?
Is one loop structure better than the other for what we need we need to create the keys for our piano?
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29. Programming Challenge
The sounds folder of the program contains the key sounds from other octaves on the piano. How would you change the octave played by the piano?
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30. One Possible Solution Changes the key sounds down one octave.
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31. Activity
Find different sound files online or use audio recorder software (e.g. Audacity) to record sounds from every day life. Move these into the sound folder of your program. Substitute these sounds for the piano sounds in your array. Create a piece of music with these sounds.
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32. Creating the Black Keys
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33. The Issue
We could go back and create everything over for the black keys that we did for the white keys, but that would not be very efficient. What we want is a Key class that will play either a white key or a black key. This is also abstraction, as we can use this method for either type of key. If we have a general Key class, the we can extend it to playing the keys for other types of instruments, say a set of trombone notes.

34. Step #1 – Instance Variable
Here we have a variable that will hold the key name of type String for either a white or black key. We also have a variable that will hold a sound. So we don’t need to make any changes from before.
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35. Step #2 – Assignment
You will need to add 2 parameters to pass the variables each time you create an instance of a key, whether it is black or white.
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36. Programming Challenge
What is the problem here?
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37. One Possible Solution (Step #1 – Instance Variable)
Create 2 more variables to show an “upImage” or a “downImage” whether it is a white or black key.
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38. One Possible Solution (Step #2 – Assignment)
Assign these variables to the constructor so they are created each time a white or black key is created.
Why do we need setImage(upImage)?
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39. Possible Compile Error
Cannot find symbol – constructor Key(java.lang.String, java.lang.String, int, int)
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40. For Loop to Create Black Keys
How can we use the white key array list to create our black keys?
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41. One Possible Solution (Step #3 –Methods)
Check to see that your methods reflect these changes.
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42. Programming Challenge
What would you need to do to be able to handle different key images? The current key is 63 pixels in width. Since this number is hard coded into our program, if we used a key image of a different size, they would not be in the same place on the board. Therefore we need to abstract this method to handle different key sizes. What would we need to do?
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43. Making the White Key Width “Unfixed” (Part I)
Create methods to return the actual width and height of a key in the Key class.
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44. Making the White Key Width “Unfixed” (Part II)
Call your “width” method in the White Key loop and change the fixed number “63” to the variable “actualWidth”.
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What would you do for the black keys?

45. Show A Message on the Board
Step #1 – At the top of the Piano class
Step #2 – At the bottom of the Piano class, under the last method.
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46. Show a Message Board (cont.)
Step #3 – Call method, in constructor.
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47. Activity
Go back to the Crab World project. Add a message that appears when the game is won. How would you make the font size bigger, or a different font? Research the java.awt.Font library.
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Steps for this are in the Crab World Project.

48. Advanced Challenge
Using fixed numbers in your code, such as 140 and 63 in the above statement is usually not the best solution. It makes your code vulnerable to breading when things change. For example is we replaced our keys with nicer keys made in PhotoShop that were of a different size, our code would not place them correctly. How would you abstract the makeKeys() method to allow for different key images.
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49. Solution – Step 1 (get height and width of keys)
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In the Key class write a method to return the width and height of your key image.

50. Solution - Step 2 (develop a formula)b
How can handled the missing black key in the 4th and 8th positions on the keyboard? h
Greenfoot determines position from the middle of the key. h2 h1 w
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What mathematical formula could be used to model key placement? H

51. Key Positions White Keys 1st Key Position 2nd Key Position
3rd Key Position
4th Key Position
(x, y)
(x, y)
(x, y)
(x, y)
w / 2, h1/2
w / 2 + w, h1/2
w / 2 + 2w, h1/2
w / 2 + 3w, h1/2
Black Keys
1st Key Position
2nd Key Position
3rd Key Position
4th Key Position
(x, y)
(x, y)
(x, y)
(x, y)
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w, h2/2
2w, h2/2
3w, h2/2
4w, h2/2

52. Solution - Step 2 (cont.) (develop a formula)b h
How can we handled the missing black key in the 3rd, 7th, and 10th positions on the keyboard? h2 h1
Greenfoot determines position from the middle of the key. w
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53. One Possible Solution – Step 3
Create a variable to hold the width of the key.
Set the width to 0.
Call the width from the Key class.
Multiplies the actual with of the key with location of the key and adds 54 which is needed to place the first key a proper distance from the edge.
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54. One Possible Solution – Step 4
Gets the width of the key.
Needed because the black keys are not the same size as the white keys.
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55. Extended Programming Challenge
Create a piano keyboard that plays different instrument sounds like a synthesizer. Collect icons of various instruments, add them to the bottom of the Piano image. When you click on one of these icons, it should change the array lists and play the set of sounds associated with that instrument, rather than the piano.
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