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New Slide Presentation: 2d arrays

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Grades are due Thursday 2/24

To be counted for this 6 week marking period I need the following assignments by Wednesday 2/23:

Create your own Fractal, Sierpinski Triangle, Palindrome Checker, Pig Latin and Google Billboard
Codingbat recursion1, recursion2, recursion3, palindrome, piglatin and googlebillboard
Recursion Worksheets #1 and 2
NOTE: minesweeper and the minesweeper codingbat will not be graded as part of this marking period
If you need help completing an assignment let me know! I’m free before school, blocks 0,4, and 6

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2 dimensional arrays

Can be thought of as a “grid” with rows and columns
Used for:

Digital Images
Board games (e.g. chess, checkers, bingo)
Maps
Tables (e.g. Periodic Table)
Spreadsheets
Seats in a theater
Days on a calendar

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2 dimensional arrays

Here’s a 2d array with 2 rows and 3 columns

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2 dimensional arrays

int [][] naNums= {{-3, -1, 5},

{7, 12, 13} };

/*Java automatically sizes the array to 2 rows and 3 columns

Note: rows first, then columns!*/

System.out.println(naNums[1][2]);

//displays 13

System.out.println(naNums[2][1]);

//Out of bounds exception!

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2 dimensional arrays

How many arrays are in the following declaration and initialization?

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

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2 dimensional arrays

There are 5 arrays total!
Each array has its own pair of curly braces: white, yellow, orange, green and red

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

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2 dimensional arrays

We can think of a 2d array as an “Array of Arrays”

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

System.out.println(alphabet[0][1]);

System.out.println(alphabet[1][0]);

System.out.println(alphabet[3][4]);

System.out.println(alphabet[4][3]);

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2 dimensional arrays

We can think of a 2d array as an “Array of Arrays”

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

System.out.println(alphabet[0][1]);

System.out.println(alphabet[1][0]);

System.out.println(alphabet[3][4]);

System.out.println(alphabet[4][3]);

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Find the output

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

System.out.print(alphabet[3][3]);

System.out.print(alphabet[0][0]);

System.out.print(alphabet[1][3]);

System.out.println(alphabet[2][4]);

System.out.println(alphabet.length);//white

System.out.println(alphabet[0].length);//yellow

System.out.println(alphabet[3].length);//red

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11

Review: Loops

Loops make things happen over and over again
If you are doing the same thing over and over again with small variations, use a loop
For example, you could write a loop to display six Xs:

X X X X X X

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Review: Loops

for(int i = ?; i <= ?; i?)

{

System.out.print("X ");

}

X X X X X X

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Review: Loops

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

X X X X X X

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Review: Nested Loops

Now, how would I repeat that pattern three times so that it looked like this?

X X X X X X

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Review: Nested Loops

for(??)

{

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

??

}

X X X X X X

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Review: Nested Loops

for(int j = 1; j <= 3; j++)

{

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

System.out.println(); //ends the line

}

X X X X X X

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Review: Nested Loops

Putting a loop inside another loop is an example of Nesting

for(int j = 1; j <= 3; j++)

{

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

System.out.println(); //ends the line

}

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Review: Nested Loops

Notice the row and column arrangement

for(int j = 1; j <= 3; j++)

{

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

System.out.println(); //ends the line

}

X X X X X X

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Review: Nested Loops

Notice the row and column arrangement

for(int j = 1; j <= 3; j++)

{

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

System.out.println(); //ends the line

}

X X X X X X

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Review: Nested Loops

Which loop is generating the three rows?
Which loop is generating the six columns?

for(int j = 1; j <= 3; j++)

{

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

System.out.println(); //ends the line

}

X X X X X X

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A good thing to remember

The outer loop can be used to generate a number of rows
The inner loop can be used to generate a number of columns

for(int j = 1; j <= 3; j++)

{

for(int i = 1; i <= 6; i++)

{

System.out.print("X ");

}

System.out.println(); //ends the line

}

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Codingbat 2d array problems

The minesweeper problem set has 10 2d array problems

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Codingbat: countFives

Click the Show Hint button and copy and paste the 2d array into the function

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Codingbat: countFives

Declare and initialize a local variable to hold the number of 5s
Write nested loops in row column order to count the number of 5s

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Nested loops

Let's say we wanted to make a 10x10 times table:

1 2 3 4 5 6 7 8 9 10

2 4 6 8 10 12 14 16 18 20

3 6 9 12 15 18 21 24 27 30

4 8 12 16 20 24 28 32 36 40

5 10 15 20 25 30 35 40 45 50

6 12 18 24 30 36 42 48 54 60

7 14 21 28 35 42 49 56 63 70

8 16 24 32 40 48 56 64 72 80

9 18 27 36 45 54 63 72 81 90

10 20 30 40 50 60 70 80 90 100

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Nested loops

Let's start with the first row

1 2 3 4 5 6 7 8 9 10

2 4 6 8 10 12 14 16 18 20

3 6 9 12 15 18 21 24 27 30

4 8 12 16 20 24 28 32 36 40

5 10 15 20 25 30 35 40 45 50

6 12 18 24 30 36 42 48 54 60

7 14 21 28 35 42 49 56 63 70

8 16 24 32 40 48 56 64 72 80

9 18 27 36 45 54 63 72 81 90

10 20 30 40 50 60 70 80 90 100

It would be easy enough to write a loop that makes the numbers 1 through 10

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Nested loops

Let's start with the first row

1 2 3 4 5 6 7 8 9 10

2 4 6 8 10 12 14 16 18 20 x2

3 6 9 12 15 18 21 24 27 30 x3

4 8 12 16 20 24 28 32 36 40 x4

5 10 15 20 25 30 35 40 45 50 x5

6 12 18 24 30 36 42 48 54 60 x6

7 14 21 28 35 42 49 56 63 70 x7

8 16 24 32 40 48 56 64 72 80 x8

9 18 27 36 45 54 63 72 81 90 x9

1020 30 40 50 60 70 80 90 100 x10

We'd put that loop inside another loop, that "multiplies" it

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Nested loops

for(int nJ = 1; nJ <= 10; nJ++)

System.out.print(nJ + "\t");

//inside loop counts columns 1 to 10

1 2 3 4 5 6 7 8 9 10

2 4 6 8 10 12 14 16 18 20 x2

3 6 9 12 15 18 21 24 27 30 x3

4 8 12 16 20 24 28 32 36 40 x4

5 10 15 20 25 30 35 40 45 50 x5

6 12 18 24 30 36 42 48 54 60 x6

7 14 21 28 35 42 49 56 63 70 x7

8 16 24 32 40 48 56 64 72 80 x8

9 18 27 36 45 54 63 72 81 90 x9

1020 30 40 50 60 70 80 90 100 x10

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Nested loops

for(int nI = 1; nI <= 10; nI++)

{

for(int nJ = 1; nJ <= 10; nJ++)

System.out.print( ?? + "\t");

??

}//outside loop counts rows 1 to 10

//(inside loop column)*outside row

//ends the line

1 2 3 4 5 6 7 8 9 10

2 4 6 8 10 12 14 16 18 20 x2

3 6 9 12 15 18 21 24 27 30 x3

4 8 12 16 20 24 28 32 36 40 x4

5 10 15 20 25 30 35 40 45 50 x5

6 12 18 24 30 36 42 48 54 60 x6

7 14 21 28 35 42 49 56 63 70 x7

8 16 24 32 40 48 56 64 72 80 x8

9 18 27 36 45 54 63 72 81 90 x9

10 20 30 40 50 60 70 80 90 100 x10

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Nested loops

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Nested loops and 2D arrays

Because 2D arrays and nested loops both work with rows and columns, they are often used together
For instance, let’s say that we wanted to display all the elements of the 2D array alphabet in row column order

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

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Nested loops and 2D arrays

This loop will loop through the 4 rows

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

for(int r = 0; r < alphabet.length; r++)

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Nested loops and 2D arrays

Then we want a second loop to loop through each of the 4 arrays

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

for(int r = 0; r < alphabet.length; r++)

for(int c = 0; c < alphabet[r].length; c++)

System.out.print(alphabet[r][c]);

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This is necessary if the rows don’t all have the same number of elements

Then we want a second loop to loop through each of the 4 arrays

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

for(int r = 0; r < alphabet.length; r++)

for(int c = 0; c < alphabet[r].length; c++)

System.out.print(alphabet[r][c]);

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You may be familiar with this 2d array where the rows don’t all have the same number of elements

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Here’s another non-rectangular 2d array where different rows have a different number of columns

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Here’s another non-rectangular 2d array where different rows have a different number of columns

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Practice Quiz Question:�Complete the 2 nested loops

Copy the following code into Processing, or fork this repl.it

String [][] words ={

{"the", "quick", "brown", "fox"},

{"jumps", "over"},

{"the", "lazy", "dog"}

};

for(int r = ??; ??; ??)

for(int c = ??; ??; ??)

System.out.print(words[r][c] + " ");

Output

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Buttons and GUIs

A GUI (Graphical User Interface) uses things like checkboxes, sliders, text fields and buttons for user input
While GUIs aren’t built in to Java or Processing, they can be added as a library
We’re going to add the Guido library to processing
(GUIdo, get it?)

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Adding Guido

Start Processing
One way is to double click on processing.exe

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Adding Guido

Choose Sketch | Import Library | Add Library

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Adding Guido

Type guido in the search box
Click on Guido by Florian Jenett to install

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Example code

Choose File | Examples
Expand Contributed Libraries | Guido and choose button

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Example code

Run the program
You should see a grid of buttons

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Adding Guido Manually

If for some reason Guido still doesn’t work, ask me for a copy of the Guido folder
Then copy the Guido folder in to Documents | Processing | Libraries

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Defining a MyButton class and using it

import de.bezier.guido.*;

private MyButton button1;

public void setup (){

size(400, 400);

textAlign(CENTER);

textSize(24);

// make the manager

Interactive.make( this );

// create a button

button1 = new MyButton( 190, 190, 20, 20 );

}

public void draw (){

background( 0 );

if(button1.isOn())

text("Button is Activated", 200, 240);

}

public class MyButton{

private float x, y, width, height;

private boolean on;

public MyButton ( float xx, float yy, float w, float h ){

x = xx; y = yy; width = w; height = h;

Interactive.add( this ); // register it with the manager

}

public void mousePressed () { on = !on;}

public void draw () {

if ( on ) fill( 200 );

else fill( 100 );

rect(x, y, width, height);

}

public boolean isOn(){return on;}

}

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Defining a MyButton class

public class MyButton

{

private float x, y, width, height;

private boolean on;

public MyButton ( float xx, float yy,

float w, float h )

{

x = xx; y = yy; width = w; height = h;

Interactive.add( this );

// register it with the manager

}

public void mousePressed () { on = !on;}

public void draw ()

{

if ( on ) fill( 200 );

else fill( 100 );

rect(x, y, width, height);

}

public boolean isOn(){return on;}

}

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Using MyButton

import de.bezier.guido.*;

private MyButton button1;

public void setup ()

{

size(400, 400);

textAlign(CENTER);

textSize(24);

// make the manager

Interactive.make( this );

// create a button

button1 =

new MyButton( 190, 190, 20, 20 );

}

public void draw ()

{

background( 0 );

if(button1.isOn())

text("Button is Activated",200, 240);

}

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In class: Copy and paste the code below and then modify it to have two larger buttons. Display the text only if both are on.

import de.bezier.guido.*;

private MyButton button1;

public void setup (){

size(400, 400);

textAlign(CENTER);

textSize(24);

// make the manager

Interactive.make( this );

// create a button

button1 = new MyButton( 190, 190, 20, 20 );

}

public void draw (){

background( 0 );

if(button1.isOn())

text("Button is Activated", 200, 240);

}

public class MyButton

{

private float x, y, width, height;

private boolean on;

public MyButton ( float xx, float yy, float w, float h )

{

x = xx; y = yy; width = w; height = h;

Interactive.add( this ); // register it with the manager

}

public void mousePressed () { on = !on;}

public void draw ()

{

if ( on ) fill( 200 );

else fill( 100 );

rect(x, y, width, height);

}

public boolean isOn(){return on;}

}

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Or fork this repl.it https://repl.it/@MrSimonLowell/ButtonPractice1

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The Game of Life

Any live cell with two or three live neighbours survives
Any dead cell with three live neighbours becomes a live cell
All other live cells die in the next generation. Similarly, all other dead cells stay dead

The Game of Life probably isn't what you think, it's a program that simulates how cells might grow or die based on a small set of rules

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Video: The Game of Life

https://www.youtube.com/watch?v=CgOcEZinQ2I&feature=youtu.be

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The Game of Life

Play the Game of Life online at playgameoflife.com

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Stable and Repeating Patterns

There are many characteristic patterns that will help you identify if your Game of Life is working correctly

images from http://pi.math.cornell.edu/~lipa/mec/lesson6.html

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Getting Started with Game of Life

If you are not sure of how to start, there is a suggested list of steps to complete the program

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create two integer constants NUM_ROWS and NUM_COLS

Constants are public, final and static
If you think of variables as “boxes”, constants are locked “boxes”
The value of a constant cannot be changed
Constants are declared outside of functions

public final static int SOME_CONSTANT = 5;

public void setup() {

//constants are NOT local to a function

}

create two integer constants NUM_ROWS and NUM_COLS

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Declaring and Initializing 2d arrays: How many rows and columns?

int [][] naNums;

naNums = new int[2][3];

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Declaring and Initializing 2d arrays: 2 rows and 3 columns

int [][] naNums;

naNums = new int[2][3];

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Declaring and Initializing 2d arrays: What would the output be?

int [][] naNums;

naNums = new int[2][3];

System.out.println(naNums[1][1]);

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Zero!�In Java, uninitialized values are 0 or equivalent

int [][] naNums;

naNums = new int[2][3];

System.out.println(naNums[1][1]);

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Now, what would the output be?

boolean [][] naNums;

naNums = new boolean[2][3];

System.out.println(naNums[1][1]);

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false�(the boolean equivalent of zero)

int [][] naNums;

naNums = new int[2][3];

System.out.println(naNums[1][1]);

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What would the output be with a String?

String [][] naNums;

naNums = new String[2][3];

System.out.println(naNums[1][1]);

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null�(the Object or pointer equivalent of zero)

String [][] naNums;

naNums = new String[2][3];

System.out.println(naNums[1][1]);

Note NO ERROR
A NullPointerException is when you try to use a null pointer
naNums[1][1].length() would cause an error

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Initializing 2 dimensional arrays

int [][] naNums;

naNums = new int[2][3];

Typically, nested loops are used to initialize each value in a 2d array. The outside loop controls the row, and the inside the column

for(int row = 0; row < 2; row++)

for(int col = 0; col < 3; col++)

naNums[row][col] = 3;

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Initializing a 2d array of Life

private Life[][] buttons;

public void setup ()

{

//other java not shown

buttons = ??

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Initializing a 2d array of Life

private Life[][] buttons;

public void setup ()

{

//other java not shown

buttons = new Life ??;

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Initializing a 2d array of Life

private Life[][] buttons;

public void setup ()

{

//other java not shown

buttons = new Life[20][20];

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Even better: use the constants!

private Life[][] buttons;

public final static int NUM_ROWS = 20;

public final static int NUM_COLS = 20;

public void setup ()

{

//other java not shown

buttons = new Life[NUM_ROWS][NUM_COLS];

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What’s the mistake?

private Life[][] buttons;

public void setup ()

{

//other java not shown

Life[][] buttons = new Life[20][20];

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buttons is declared twice

private Life[][] buttons;

public void setup ()

{

//other java not shown

Life[][] buttons = new Life[20][20];

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How many new Lifes have been created? (Hint: it's a trick question)

private Life[][] buttons;

public void setup ()

{

//other java not shown

buttons = new Life[20][20];

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Another way to ask the question would be: “What value is in each cell of buttons after this code executes?”

Hint: look back at slides 61 & 62

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None yet! Imagine an array with 20 rows and columns each of which is empty

private Life[][] buttons;

public void setup ()

{

//other java not shown

buttons = new Life[20][20];

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Use nested loops in row column order to initialize buttons

private Life[][] buttons;

public void setup ()

{

//other Java code not shown

for(int r = ??; r < ??; r++)

for(int c = ??; c < ??; c++)

buttons[r][c] = new Life(??,??);

//other Java code not shown

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Notice the Life constructor takes 2 arguments, the row and the column

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Getting the grid to appear

Just a couple more steps and you should have a grid of buttons
Uncomment the first two lines in the Life constructor public Life (int row, int col)
In draw under the comment //use nested loops to draw the buttons here write nested loops (again using the constants) to draw each button to the screen.

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Getting the grid to appear

Run the program, you should now see a random grid of buttons similar to the picture below. If you click on the button it should turn off and on.

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76

Video: Conway’s Game of Life Part 2

https://www.youtube.com/watch?v=m4LtaZNHN9E

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Counting Neighbors

The life and death of cell depends on the 8 neighbors that surround it

create two integer constants NUM_ROWS and NUM_COLS

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Counting Neighbors

If a living cell has fewer than two or more than three living neighbors it dies

create two integer constants NUM_ROWS and NUM_COLS

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Counting Neighbors

If an empty cell has exactly three living neighbors it comes to life

create two integer constants NUM_ROWS and NUM_COLS

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The 8 possible neighbors

Here are the 8 possible neighbors of a cell at (row,col)

create two integer constants NUM_ROWS and NUM_COLS

(row, col)

(row, col-1)

(row, col+1)

(row+1, col)

(row+1, col-1)

(row+1, col+1)

(row-1, col)

(row-1, col-1)

(row-1, col+1)

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Counting Neighbors

Cells on the corners and edges of the grid will have less than 8 valid neighbors

create two integer constants NUM_ROWS and NUM_COLS

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What are valid cells?

Valid means the cell exists, it’s on the grid
Positions that would be outside the edges of the grid are not valid

create two integer constants NUM_ROWS and NUM_COLS

valid

not valid

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83

Codingbat

You may find it helpful to do these four codingbat problems before you code isValid and countNeighbors in the Game of Life

create two integer constants NUM_ROWS and NUM_COLS

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84

Game of Life due date 3/12

codingbat minesweeper problem set due tomorrow Friday March 5
Game of Life due one week from tomorrow Friday March 12

create two integer constants NUM_ROWS and NUM_COLS

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85

Spraypaint Game of Life

Here’s an interesting version of the Game of Life

www.fractalteapot.com/portfolio/game-of-life/

create two integer constants NUM_ROWS and NUM_COLS

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Why do we need the “buffer”?

In computer graphics a buffer typically stores the value for each pixel shown on the display
We’ll use the buffer to store a snapshot of the grid
If we don’t use a buffer, the result doesn’t work correctly as you can see in this animation that doesn’t use a buffer

create two integer constants NUM_ROWS and NUM_COLS

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Why do we need the “buffer”?

The buffer allows us to store the current state of the grid and “freeze” it in time
It allows us to apply the rules to all cells simultaneously
You can see that this correct animation that uses a buffer gives a completely different result

create two integer constants NUM_ROWS and NUM_COLS

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Why do we need the “buffer”?

First, we need to go through the entire array and count the neighbors of every cell . . .

create two integer constants NUM_ROWS and NUM_COLS

0

1

2

0

1

2

3

2

0

1

2

1

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Why do we need the “buffer”?

. . . and then apply the rules to all the cells at the same time

create two integer constants NUM_ROWS and NUM_COLS

0

1

2

1

0

1

0

1

2

1

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Why do we need the “buffer”?

In this example none of the cells survive

create two integer constants NUM_ROWS and NUM_COLS

0

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Quizziz

create two integer constants NUM_ROWS and NUM_COLS

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92

Getting Started with Minesweeper

If you are not sure of how to start, there is a suggested list of steps to complete the program

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93

create two integer constants NUM_ROWS and NUM_COLS

Your program should run without errors after you complete each step

create two integer constants NUM_ROWS and NUM_COLS

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94

initialize the 2d array buttons

Remember to use your constants for the number of rows and columns!

create two integer constants NUM_ROWS and NUM_COLS

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95

Use nested loops to create a new MSButton for each row column pair

Remember to use your constants for the number of rows and columns!

create two integer constants NUM_ROWS and NUM_COLS

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96

Uncomment the first two lines of the MSButton constructor

You should now see a grid of buttons
If you click on the button it should turn white

create two integer constants NUM_ROWS and NUM_COLS

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97

go to line 7, and initialize bombs to be a new empty ArrayList of type MSButton

create two integer constants NUM_ROWS and NUM_COLS

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98

Add code to the setBombs() function

It should generate a random row and column number
Remember to use your constants for the number of rows and columns!

create two integer constants NUM_ROWS and NUM_COLS

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99

Uncomment the 3rd and 4th lines of MSButton draw()

Add the button at the random location to bombs
To test your program, print that location, click the button and check if the button turns red

create two integer constants NUM_ROWS and NUM_COLS

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100

Add a while loop in setBombs()

Use the contains() function to check to see if the button at the random location is already in bombs. If it isn't then add it
Test your program repeatedly to make sure you are getting the correct number of bombs

create two integer constants NUM_ROWS and NUM_COLS

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Recursion in Minesweeper

If you press a button that has no mine count the 8 adjacent buttons are also pressed
If any of those neighbors have no mine count, their 8 neighbors are also pressed
And so on. . .

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Remove marked blobs to the left

Problem: Write code so that when a blob is clicked any adjacent marked blobs to the left are also unmarked

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What would happen if I clicked on the indicated blob?

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Remove marked blobs to the left

Problem: Write code so that when a blob is clicked any adjacent marked blobs to the left are also unmarked

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Remove marked blobs to the left

Problem: Write code so that when a blob is clicked any adjacent marked blobs to the left are also unmarked

104

Now what would happen if I clicked on the indicated blob?

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Remove marked blobs to the left

Problem: Write code so that when a blob is clicked any adjacent marked blobs to the left are also unmarked

105

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Remove marked blobs to the left

Problem: Write code so that when a blob is clicked any adjacent marked blobs to the left are also unmarked

106

Now what would happen if I clicked on the indicated blob?

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Remove marked blobs to the left

Problem: Write code so that when a blob is clicked any adjacent marked blobs to the left are also unmarked

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Remove marked blobs to the left

The blobs are in a two dimensional array called blobs
The Blob class has private member variables for the row and column

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Remove marked blobs to the left

The Blob class has public member functions isValid() and isMarked()

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Practice Quiz Question

import de.bezier.guido.*;

private Blob[][] blobs;

void setup ()

{

size(400, 400);

// make the manager

Interactive.make( this );

blobs = new Blob[10][10];

for (int r = 0; r < 10; r++)

for (int c = 0; c < 10; c++)

blobs[r][c] = new Blob(r, c);

}

void draw() {

}//empty

public class Blob

{

private int r, c;

private float x, y, width, height;

private boolean marked;

public Blob ( int rr, int cc )

{

width = 40;

height = 40;

r = rr;

c = cc;

x = c*width;

y = r*height;

marked = Math.random() < .5;

Interactive.add( this ); // register it with the manager

}

public boolean isMarked()

{

return marked;

}

public boolean isValid(int row, int col)

{

if (row>=0 && row<10 && col>=0 && col<10)

return true;

else

return false;

}

public void mousePressed ()

{

marked = false;

//your code here

//if position to left is valid and marked

//call mousePressed for the blob on left

}

public void draw ()

{

if (marked)

fill(50);

else

fill( 255 );

rect(x, y, width, height);

fill(0);

}

110

Copy the code on this slide (#90) into Processing
Replace the comments on lines 49-51 with an if statement so that if there is a valid position on the left and the blob to the left is marked, mousePressed is recursively called for the blob to the left
Hint: what’s to the left of blobs[r][c]?

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marked vs clicked

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The MSButton class has two boolean member variables

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contains

Returns true or false if an ArrayList or String contains an element.
Good for eliminating duplicate values

ArrayList <Integer> arlist =

new ArrayList <Integer>();

arlist.add(3);

System.out.println(arlist.contains(2));

arlist.add(2);

System.out.println(arlist.contains(2));

System.out.println(arlist);

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contains

Returns true or false if an ArrayList or String contains an element.
Good for eliminating duplicate values

ArrayList <Integer> arlist =

new ArrayList <Integer> ();

arlist.add(3);

System.out.println(arlist.contains(2));

arlist.add(2);

System.out.println(arlist.contains(2));

System.out.println(arlist);

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contains

Returns true or false if an ArrayList or String contains an element.

String str = new String("The best thing about a boolean is even if you are wrong, you are only off by one.");

System.out.println(str.contains("worst"));

System.out.println(str.contains("best"));

System.out.println(str.contains("z"));

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contains

Returns true or false if an ArrayList or String contains an element.

String str = new String("The best thing about a boolean is even if you are wrong, you are only off by one.");

System.out.println(str.contains("worst"));

System.out.println(str.contains("best"));

System.out.println(str.contains("z"));

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Checking if it doesn’t contain something

Often, you want to know if the ArrayList doesn’t contain a value

ArrayList <Integer> arlist =

new ArrayList <Integer> ();

arlist.add(1);

arlist.add(2);

if(!arlist.contains(3)) //doesn’t contain 3

arlist.add(3);

System.out.println(arlist);

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Checking if it doesn’t contain something

Often, you are more interested if the ArrayList doesn’t contain a value

ArrayList <Integer> arlist =

new ArrayList <Integer> ();

arlist.add(1);

arlist.add(2);

if(!arlist.contains(3)) //doesn’t contain 3

arlist.add(3);

System.out.println(arlist);

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Practice Quiz Question:�Find the output

int [] array = {4,-2,4,3,7,-2,4,6};

ArrayList <Integer> arlist =

new ArrayList <Integer> ();

for(int i = 0; i < array.length; i++)

if(!arlist.contains(array[i]))

arlist.add(array[i]);

System.out.println(arlist);

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119

Replace the comments on lines 49-51 with an if statement so that if there is a valid position on the left and the blob to the left is marked, recursively call mousePressed for the blob to the left

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120

Replace the comments on lines 49-51 with an if statement so that if there is a valid position on the left and the blob to the left is marked, recursively call mousePressed for the blob to the left
How would you check if there is a valid position on the left?
How would you check if the blob to the left is marked?
How would you call mousePressed for the blob to the left?

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What is the output?

public void setup() {

Thingy bob = new Thingy(5);

Thingy notBob = new Thingy(7);

bob.mystery();

}

class Thingy {

private int myNum;

public Thingy(int n) {

myNum = n;

}

public void mystery() {

System.out.println(myNum);

}

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this

means "the object in front of the dot"

public void setup() {

Thingy bob = new Thingy(5);

Thingy notBob = new Thingy(7);

bob.mystery();

}

class Thingy {

private int myNum;

public Thingy(int n) {

myNum = n;

}

public void mystery() {

System.out.println(this.myNum);

}

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this

means "the object in front of the dot"

public void setup() {

Thingy bob = new Thingy(5);

Thingy notBob = new Thingy(7);

bob.mystery();//displays 5

}

class Thingy {

private int myNum;

public Thingy(int n) {

myNum = n;

}

public void mystery() {

System.out.println(this.myNum);

}

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this

Now, in this particular case, this isn't necessary

public void mystery() {

System.out.println(this.myNum);

}

Could be replaced with just

public void mystery() {

System.out.println(myNum);

}

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public void setup() {

Thingy bob = new Thingy(5);

Thingy notBob = new Thingy(7);

bob.mystery();

}

class Thingy {

private int myNum;

public Thingy(int n) {

myNum = n;

}

public void mystery() {

System.out.println(this);

}

public String toString(){

return "My number is " + myNum;

}

125

Sometimes however, the is no other way to write the code

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System.out.println(this);

is the same as

System.out.println(this.toString());

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Remember that in Java, sending an object to System.out.println or System.out.print automatically calls toString()

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Because this is used as an argument, there is no other way to get the code to work

public void setup() {

Thingy bob = new Thingy(5);

Thingy notBob = new Thingy(7);

bob.mystery();

}

class Thingy {

private int myNum;

public Thingy(int n) {

myNum = n;

}

public void mystery() {

System.out.println(this);

}

public String toString(){

return "My number is " + myNum;

}

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bob doesn't work. bob is out of scope.

public void setup() {

Thingy bob = new Thingy(5);

Thingy notBob = new Thingy(7);

bob.mystery();

}

class Thingy {

private int myNum;

public Thingy(int n) {

myNum = n;

}

public void mystery() {

System.out.println(bob); //ERROR!

}

public String toString(){

return "My number is " + myNum;

}

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this

is a Java keyword (it has particular meaning in Java)
means "the object in front of the dot" or "the object that called the function" e.g. bob.mystery();
Good style: Should be used only rarely, only use this when you are required to
Is only required when you need to pass the object that called the function as an argument e.g.

System.out.println(this);

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2 Part Practice Quiz Question:�A. Find the output�B. Identify which two uses of this are unnecessary

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public void setup() {

WhatsIt bob = new WhatsIt('a', 1);

WhatsIt notBob = new WhatsIt('b', 2);

notBob.mystery();

}

class WhatsIt {

private char myChar;

private int myNum;

public WhatsIt(char c, int n) {

myChar = c;

myNum = n;

}

public void mystery() {

System.out.println("char is " + this.myChar);

System.out.println(this);

}

public String toString(){

return "number is " + this.myNum;

}

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In Class:

Write a small program in processing that uses nested loops to produce the following output

�

Use appropriate variable names in your loops like row and col

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"\t" is tab

Write a small program in processing that uses nested loops to produce the following output

(5,0) (5,1) (5,2) (5,3) (5,4) (5,5) (5,6) (5,7)

You may find this helpful:

System.out.print("("+row +","+col+")"+"\t");

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133

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134

Nested loops and graphics

Let's say I wanted to make a grid of circles that looked like this
I can tell it has 8 rows and 6 columns
So I'll need appropriate loops

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135

One loop will make the x coordinates and the other the y

for( ?? ) //8 rows

{

for( ?? ) //6 columns

{

ellipse(x,y,5,5);

}

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136

If I move down one row, what's changing, x or y?

for( ?? ) //8 rows

{

for( ?? ) //6 columns

{

ellipse(x,y,5,5);

}

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137

The outer loop changes y and the inner loop changes x

for(int y = ?? ; y <= ?? ; y ?? ) //8 rows

{

for(int x = ?? ; x <= ?? ; x ?? //6 columns

{

ellipse(x,y,5,5);

}

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138

The outer loop changes y and the inner loop changes x

for(int y = 10 ; y <= 80 ; y +=10 ) //8 rows

{

for(int x = 20 ; x <= 70 ; x +=10 //6 columns

{

ellipse(x,y,5,5);

}

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139

The outer loop changes y and the inner loop changes x

for(int y = 10 ; y <= 80 ; y +=10 )

//8 rows at 10 20 30 40 50 60 70 80

{

for(int x = 20 ; x <= 70 ; x +=10

//6 columns at 20 30 40 50 60 70

{

ellipse(x,y,5,5);

}

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140

Practice Quiz Question

Write a program using nested loops that will create a similar pattern of ellipses

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Practice Quiz Question

import de.bezier.guido.*;

private Blob[][] blobs;

public final static int NUM_ROWS = 15;

public final static int NUM_COLS = 12;

void setup ()

{

size(400, 400);

// make the manager

Interactive.make( this );

blobs = new Blob[NUM_ROWS][NUM_COLS];

for(int r = 0; r < NUM_ROWS; r++)

for(int c = 0; c < NUM_COLS; c++)

blobs[r][c] = new Blob(r,c);

}

void draw(){}//empty

public class Blob

{

private int myRow, c;

private float x,y, width, height;

private boolean marked;

public Blob ( int rr, int cc )

{

width = 400/NUM_COLS;

height = 400/NUM_ROWS;

myRow = rr;

c = cc;

x = c*width;

y = myRow*height;

marked = Math.random() < .5;

Interactive.add( this ); // register it with the manager

}

public boolean isMarked()

{

return marked;

}

public boolean isValid(int row, int col)

//post condition: returns true if both row and col are valid, false otherwise

{

//your code here

return false;

}

public void mousePressed ()

{

if(marked == true)

{

marked = false;

if(isValid(myRow,c-1) && blobs[myRow][c-1].isMarked())

blobs[myRow][c-1].mousePressed();

//3 more recursive calls

}

public void draw ()

{

if (marked)

fill(50);

else

fill( 255 );

rect(x, y, width, height);

fill(0);

}

141

Copy the code on the right into processing
On line 42 add code to complete the isValid function
On line 53 add 3 recursive calls to the mousePressed function
The finished program should remove marked blobs up, down, left and right
On lines 3 and 4 change the number of rows and columns, and check to see that your program still works correctly

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The call to isValid is first

Note that we call isValid() first before the calls to isMarked() and mousePressed()
If isValid() returns false, the other code won’t be executed
That is an example of short circuit evaluation

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Constants are public, final and static

If you think of variables as boxes, constants are locked boxes
The value of a constant cannot be changed

public final static int SOME_CONSTANT = 5;

public void setup() {

//java code not shown

}

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Constants are public, final and static

public means available in the entire program

public final static int SOME_CONSTANT = 5;

public void setup() {

//java code not shown

}

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Constants are public, final and static

final means “locked”

public final static int SOME_CONSTANT = 5;

public void setup() {

//java code not shown

}

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Constants are public, final and static

static means “only one” (more on this later)

public final static int SOME_CONSTANT = 5;

public void setup() {

//java code not shown

}

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Constants are public, final and static

int is the type of constant

public final static int SOME_CONSTANT = 5;

public void setup() {

//java code not shown

}

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Constants are public, final and static

SOME_CONSTANT is the name

public final static int SOME_CONSTANT = 5;

public void setup() {

//java code not shown

}

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Constants are public, final and static

Here is a simple Thingy class

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Constants are public, final and static

And here are a couple instances of the Thingy class
What’s the output?

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Constants are public, final and static

And here are a couple instances of the Thingy class
What’s the output?

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Constants are public, final and static

Now let’s change num to be static

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Constants are public, final and static

When I run the same program again, the output is 3!

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Constants are public, final and static

A static variable is shared by all instances of the class

154

bob

notBob

2

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Constants are public, final and static

A static variable is shared by all instances of the class

155

bob

notBob

3

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Constants are public, final and static

Since there is only one static variable that is shared by all instances of the class, it doesn’t matter if I use bob.num notBob.num or even Thingy.num

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A common beginner mistake

Can you spot the common mistake beginning programmers often make?

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A common beginner mistake

Unfortunately, beginning programers don’t understand the “Cannot make a static reference” error message

158

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static variables and functions

static variables and functions are “shared”
Only one variable and/or function is shared by all instances of the class
static avoids unnecessary duplicates

159

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static variables and functions

Constants are usually static because they only store a single value
static functions don’t use member variables

160

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Practice Quiz Question:�Which line will cause an error?

Thingy bob = new Thingy();

bob.num = 6;

Thingy sam = new Thingy();

sam.num = 7;

System.out.println(bob.getNum());
System.out.println(sam.getNum());
System.out.println(Thingy.getNum());
System.out.println(bob.addNums(3,4));
System.out.println(sam.addNums(5,6));
System.out.println(Thingy.addNums(2,-2));
System.out.println(bob.E);
System.out.println(sam.E);
System.out.println(Thingy.E);

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for each loops & 2D arrays

Note that each row is a char[] character array

char [][] alphabet ={

{'a','b','c','d','e','f','g'},

{'h','i','j','k','l','m','n'},

{'o','p','q','r','s','t','u'},

{'v','w','x','y','z'}

};

for(char[] row: alphabet)

for(char letter: row)

System.out.print(letter);

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In class: Modify your previous program to display the x coordinate of the last button that was clicked

Hint: On the third line of your program create a private float theX
In mousePressed set theX to the x coordinate

163