cse 8a lecture 10cse8afall.weebly.com/uploads/1/3/4/1/13415552/lec10after...cse 8a lecture 10...

CSE 8A Lecture 10

• Reading for next class: 6.3

• PSA4 Interview: due tomorrow, don’t forget

• PSA5: Posted (get started)

• Today (random useful stuff):

– Variable scope

– Returning a value

– Static methods

– Comments

– If-statements

1. Two colors are considered "distant" if:

READING QUIZ – NO TALKING – CORRECTNESS MATTERS

A. If all three color components (red, green, blue)

are different

B. If two of the color components are different

C. If they are distant in a 3-dimensional RGB space

D. If any one component is distant

2. If I wanted the following lines to print “if statement was true” what could go in the blank to do this? int x = 30;

if(_______)

System.out.println(“if statement was true);

A. x>30 B. x<30 C. x<0 D. x>0


3. The following method loops through each pixel in an image checking if the distance between the color in the current picture is less that 50 away from the color red (defined as red = 100, green = 0, blue = 0). If the distance between the current color and the defined red is less than 50, the red and blue color values of that pixel are set to 0. What needs to go in the blank to complete this method. public void turnRedIntoGreen()

{

Color red = new Color(100,0,0);

Pixel[] pixelArray = this.getPixels();

Pixel pixel = null;

//loop through the pixels

for(int index = 0; index<pixelArray.length; index++)

{

pixel = pixelArray[index]

//if dist between current color and red is less than 50

if (____________________________)

pixel.setColor(new Color(0, pixel.getGreen(), 0));

}

}

A. pixel.colorDistance(red) < 50.0

B. pixel.getRed() < 50.0

C. pixel.getColor() < red READING QUIZ – NO TALKING – CORRECTNESS MATTERS

4. What gets printed in the following: int x = 12, r = 10;

if(x < 12)

{

x = 100;

}

else

{

r = r + 20;

}

System.out.prinln(x+r);

A. 34

B. 110

C. 42

D. 80


Thank you for your feedback!

• Just a couple more questions…

How do you feel about the pace of the class?

A. Way too slow

B. A little too slow

C. Just about right

D. A little too fast

E. Way too fast



How do you feel about the difficulty of the PSAs?

A. Way too short/easy

B. A little too short/easy

C. Just about right

D. A little too long/hard

E. Way too long/hard



How many hours to do you spend outside of class per week?

A. 0-1:59:59

B. 2-3:59:59

C. 4-5:59:59

D. 6-8:59:59

E. 9 or more

Feedback on Feedback

• What you want to keep:

– CLICKER QUESTIONS/Group discsusion/Peer

instruction!

– Energy/enthusiasm

– Clearly explaining code (Box-and-arrow diagrams!)

– Posting slides online


• What you want to keep:

– CLICKER QUESTIONS/Group discussion/Peer

instruction!

– Energy/enthusiasm

– Clearly explaining code (Box-and-arrow diagrams!)

– Posting slides online

“The only thing that would make this class better is

if free donuts were handed out while people massaged our feet”


• What you want to quit (most feedback under

“start”):

– Pair programming

– Exams that lag behind current material

– Too much time for group discussion (but many say not

enough time…)


• What you want to start:

– Review session/practice problems

• We will try to provide these, but remember, you have “practice problems” already (and as you

advance in college you will be expected to generate your own)

– More office hours

• I’m always available by appointment

– Work with same partner more

• Change: You can work with the same partner up to 3 times

– Real-world applications /stuff not in book

• Sound good!

– Posting slides clean and with comments

• Will do!

– Running code/writing code in class

• Yup! (But writing without running is still an important skill)

– More challenges on PSAs

• Coming up!

– Make the classroom warmer (Sorry, bring a sweater)

Interm Exam 2

• WOW! Nice job!

– Median: 9.5

– High score: 10 (208 of these!)

• Exams provide a minimum bar sanity check

• If you scored lower than a 7, it’s time to REALLY

take action

– Come to the lab/office hours and get help

– Re-do all of the lab quizzes, clicker questions, reading

questions, etc.

Exam Problem 1 // for loop version

public void maxBlue()

{

Pixel p;

Pixel[] pixArray = this.getPixels();

for (int index = pixArray.length/2; index<pixArray.length; index++)

{

p = pixArray[index];

p.setBlue(255);

}

}

// while loop version

public void maxBlue()

{

Pixel p;


int index = pixArray.length/2;

while (index < pixArrray.length )

{

p = pixArray[index];

p.setBlue(255);

index++;

}

}

Exam Problem 2

Pixel[] pixArr = this.getPixels();

int index = 0;

while (index < pixArr.length)

{

pixArr[index].setBlue(0);

___________________________________________;

index++;

}

Exam Problem 3 public void swapRedGreen()

{


for (int index = 0; index<pixArray.length; index++)

{

Pixel p = pixArray[index];

p.setRed( p.getGreen() );

p.setGreen( p.getRed() );

}

}

WHOOPS!

red

green

p

Parameters and scope In Picture.java…

public void copyRegionTo (Picture target, int xSource,

int ySource, int xTarget, int yTarget )

{

// Body omitted to save space

}

In main…

Picture fish = new Picture( "fish.jpg" );

Picture blank = new Picture();

fish.copyRegionTo(blank, 10, 50, 30, 30);

Variables only exist in the region they are defined.

I.e. variables in main cannot be accessed in copyRegion and vice versa

The region where a variable exists is called its scope




{

Pixel sPixel, tPixel = null;

for (int sX = xSource, tX = xTarget; sX < 100+xSource; sX++, tX++)

{

for (int sY = ySource, tY = yTarget; sY < 100+ySource; sY++, tY++)

{

sPixel = this.getPixel(sX,sY);

tPixel = target.getPixel(tX,tY);

tPixel.setColor(sPixel.getColor());

}

}

}

In main… Picture fish = new Picture( "fish.jpg" );



Main’s variables

fish

blank



{



{


{




}

}

}





Main’s variables

fish

blank

copyRegionTo’s variables

target

this

xSource

ySource

xTarget

yTarget

Also sX, tX, sY, sY,

sPixel, tPixel

fish

blank





Main’s variables

fish

blank



{



{


{




}

}

}

Parameters and return values In Picture.java… public Picture copyRegionToNew(int xSource,


{

Picture newCanvas = new Picture();



{


{


tPixel = newCanvas.getPixel(tX,tY);


}

}

}


Picture newCanvas = fish.copyRegionToNew(10, 30, 50, 50);

newCanvas.show();

What error will the following code produce?

A. This code will not compile

B. The line “Picture newCanvas = fish.copyRegionToNew…” in main will cause an error

C. The line newCanvas.show() will cause an error

Parameters and return values In Picture.java… public Picture copyRegionToNew(int xSource,


{




{


{




}

}

}


Picture newCanvas = fish.copyRegionToNew(10, 30, 50, 50);

newCanvas.show();

fish

newCanvas

Some of copyRegionTo’s

variables main’s variables

newCanvas

this

Some comments on comments /* A method to copy a 100x100 region of the calling object’s

* image to a blank canvas.

* xSource, ySource: the upper left corner of the

* region to be copied.

* xTarget, yTarget: the upper left corner where the region

* will appear in the new canvas.

* returns a new canvas with the region copied into it. */

public Picture copyRegionToNew(int xSource,


{




{


{




}

}

return newCanvas;

}

Header (method) comments required.

Inline comments if necessary

Unraveling the magic of main

public static void main( String[] args )

Still a bit mysterious, for now

Doesn’t return anything

Parameters (how are these

passed in?)

Method name

Who “owns” the method…

Classes vs. Objects In the code below, how many classes are there? How many objects?

(And what does the memory model look like?)

Picture p = new Picture( “fish.jpg” );

Picture p2 = new Picture( p );

Picture p3 = p2;

A. 1 class, 2 objects

B. 1 class, 3 objects

C.2 classes, 2 objects

D.2 classes, 3 objects

E. 3 classes, 2 objects

Classes vs. Objects In the code below, how many classes are there? How many objects?

(And what does the memory model look like?)

Picture p = new Picture( “fish.jpg” );

Picture p2 = new Picture( p );

Picture p3 = p2;

The Picture class

Picture objects

new new

p

p3

p2 variables

variables

Static vs. nonstatic methods

Picture result =

Picture.collage(p1, p2, p3);

(nonstatic)

public class Picture{ ... public static Picture collage(Picture p1, Picture p2, Picture p3) public void filter1()

Picture p =

new picture( “fish.jpg”);

p.filter1();

Class - owned

Object - owned

static

the Picture p

collage

filter1

the Picture class

the Picture p1

the Picture p2

the returned

Picture

the Picture p3

Static vs. nonstatic methods

Picture result =

Picture.collage(p1, p2, p3);

(nonstatic)

public class Picture{ ... public static Picture collage(Picture p1, Picture p2, Picture p3) public void filter1()

Picture p =

new picture( “fish.jpg”);

p.filter1();

Class - owned

Object - owned

static

the Picture p

collage

filter1

the Picture class

the Picture p1

the Picture p2

the returned

Picture

the Picture p3

Static methods can be called directly on the class (can also be called on an object)

Non-static methods must be called on an object

Unraveling the magic of main

public static void main( String[] args )

Still a bit mysterious, for now

Doesn’t return anything

Parameters (how are these

passed in?)

Method name

Who “owns” the method…

Why does main have to be static? (Discuss with group)

Chapter 6: Conditionally modifying pixels

All pixels change if COLOR

meets criteria

All pixels change if meet both a

COLOR and COORDINATE criteria

All pixels change if COORDINATES

meet criteria

Select the if statement to make bottom half of picture some color

1) Solo: (30 sec)

2) Discuss: (1 min)

3) Group: (30 sec)

public void fillBottom(Color newColor)

{

Pixel pix;

for (int y = 0; y < this.getHeight(); y++)

{

for (int x = 0; x < this.getWidth(); x++)

{

<<<SELECT LINE OF CODE>>>>

{

pix = this.getPixel(x,y);

pix.setColor(newColor);

}

}

}

A) if(y<this.getHeight()/2)

C) if (this.getPixel(x,y) < this.getHeight()/2)

B) if(y>this.getHeight()/2)

D) if (this.getPixel(x,y) > this.getHeight()/2)

Does the order of the for loops matter?

1) Solo: (30 sec)

2) Discuss: (1 min)

3) Group: (30 sec)

public void fillBottom(Color newColor) {

Pixel pix;

for (int y = 0; y < this.getHeight(); y++)

{

for (int x = 0; x < this.getWidth(); x++)

{

<<<SELECT LINE OF CODE>>>>

{

pix = this.getPixel(x,y);

pix.setColor(newColor);

}

}

} A. Yes, since we are changing the bottom half, we have to “fill in” across the rows in the inner loop

B. Yes, because we need to make sure the if statement is checking y not x

C. No, the if statement controls the assignment

Real-world example of if-else rules (among other things)

Eamonn Keogh, UCR

ALARM!

Temp too high!

if (temp > 104.0)


Eamonn Keogh, UCR

TRILLIONS of data points

(or more!)

How long would it take to loop through this data?

How could you find patterns?


Eamonn Keogh, UCR

Usually, the sensors only display the last

few minutes of data and figures such as

the minimum and maximum temperature

for that day. In most cases, the rest of the

data is discarded.

This is in part due to legal and privacy

issues, which the researchers believe can

be solved. It’s also because computer

scientists didn’t have the tools to mine the

vast amounts of data produced in pediatric

intensive care units.

That changed after Keogh and a group of

researchers recently developed a new

technique, which allows for searching of

datasets with more than one trillion objects.

That’s a larger set than the combined size

of all datasets in all data mining papers

ever published.

http://ucrtoday.ucr.edu/9667


Eamonn Keogh, UCR

Keogh plans to use the archived data to

develop algorithms that incorporate what

he calls “if then rules” that can assist

doctors. For example, if a heart beat looks

like this, then a child may have difficulty

breathing in five seconds.

http://ucrtoday.ucr.edu/9667

Summary of Concepts

• Variable scope

• Good commenting style

• If statements

• Efficiency

TODO

• Reading for next class: 6.3

• Start PSA5

cse 8a lecture 10cse8afall.weebly.com/uploads/1/3/4/1/13415552/lec10after...cse 8a lecture 10...

Documents