Questions on HW1-Spring08

Questions on HW1-Spring08

Ask questions on homework 1 here:

Question: Is the deadline still Friday at 7pm? T-square still isn't up

T-square will be ready for homework 1. Dawn Finney.

Question: Should our homework return 2 pictures with one modification made on each, or should it return 1 picture with two modifications made?

The first one. Dawn Finney.

Question: How do we find out who our grading TA is or should we just put which section we are in or is it both TA's in the recitation? I can't find it...

Grading TAs haven't been assigned yet. We'll probably send out an email when the TAs have been assigned. Your grading TA will more than likely be one of the two TAs that teach your section (excluding me. I don't think I'll be grading homeworks). Dawn Finney.

Question: I'm having trouble figuring out how you build the code, like grayscale or decreaseRed. I'm sure that's the point of this homework, but is there anywhere where we can see more examples?

What do you mean by build the code? The best examples to look at are in the Picture class itself. Dawn Finney.

Question: How do I get my code to run through every pixel in the picture instead of just one pixel? Isn't there a certain line of code to use? Is that what "Pixel[] getPixels()" is for? Even if it's not, can you explain what that piece means?

You really should have gone over this in recitation Monday. Yes you do need the line Pixel[] pixarray = this.getPixels();. This line makes it so that pixarray is an array of all of the Pixels in the picture. Then just use a for loop or a while loop to iterate through all of the Pixels. If you are still confused, feel free to look at the recitation guide from Monday. Dawn Finney.

Question: Is it normal that I have to open and compile filechoose.java in addition to my code before I can open any pictures/getMediaPath?

It is not normal to have to recompile FileChooser every time, however you will have to compile your code each time before running it. I don't think I've compiled FileChooser again since the first time I used it. It is possible your classpaths are not set correctly. Joel Uthe

Question: After copying and pasting something into my code (before modifying it) I get an error for the line "public void verticalLines()" saying that it's an "illegal start of expression." Translation?

Is it included within the class file, more specifically within the
```
public class AdvancedPicture{...//all code goes in here}
```
. Joel Uthe

Question: I made sure my 'verticaLines' was within the class file, but I'm still getting the "illegal start of expression" error. What should I do? :(

It needs to be inside of the class declaration but not within any other methods. Dawn Finney.

Question: Thanks! ... but concerning the Filechooser question, how do I fix it?

Reread the setting up Dr. Java section and pay attention to part where you have to edit Dr. Java's preferences to include the java sources in the classpaths. Dawn Finney.

Question: Since we have to use FileChooser.getMediaPath(), do we include a picture name in the parenthesis, or will the grading TA do that? Also, will our TA be setting the MediaPath?

We TAs have our own mediapaths set up. You have to include a picture from mediasources in the parenthesis of FileChooser.getMediaPath(). Dawn Finney.

Question: I keep getting an error message that says I have no 'main' method in 'AdvancedPicture'. This is that part of the code...what am I missing?

 public static void main(String [] args) {
    AdvancedPicture ap1 = new AdvancedPicture(FileChooser.getMediaPath("bigben.jpg"));
    AdvancedPicture ap2 = new AdvancedPicture(FileChooser.getMediaPath("shops.jpg"));
    ap1.grayscale();
    ap1.show();   
    ap2.decreaseRed();
    ap2.show();
  }

Maybe you need to compile the file. Your main method looks fine but I hope those aren't the methods you are planning to turn in for the homework. Dawn Finney.

Question: For some reason my filechooser is not working properly my code looks like...

    AdvancedPicture ap1 = new AdvancedPicture(FileChooser.getMediaPath("arch.jpg "));
    AdvancedPicture ap2 = new AdvancedPicture(FileChooser.getMediaPath("eiffel.jpg "));

The error I get is a picture popping out saying "Couldn't load D:/cs1316/mediasources/eiffel.jpg" which is weird because I don't have a D drive. Also I know everything else works because when I hardcode the file path everything works properly.

You need to set your mediapath. Dawn Finney.

Question: Do we need to put into our code the "public String toString() {}" part?

No. Dawn Finney.

I compile my program with no problems, but when I try to run it, I am getting "Couldn't load the file D:/cs1316/mediasources/swan.jpg". I compiled the FileChooser.java file, set my media paths according to the instructions, and don't know what can be going wrong. I'm using a Mac, if that may hold any bearing as to the source of the issue? Any suggestions?

Double check the mediapath and reset it again. See what happens....computer dying.....Dawn Finney.

Same deal...if I type "java AdvancedPicture" in the Interactions Pane, I get "Couldn't load the file D:/cs1316/mediasources/swan.jpg", however, if I compile again and click the run button, I get "Couldn't load the file nullswan.jpg". BAH! =(

REMOVEDces are the the D: drive is your CD drive. You need to make sure that you copy the files required onto the computer and can run the program without the CD in the drive (the best way to do this is to eject the cd to make sure). Also make sure you set your mediapath once (using FileChooser.setMediaPath("mydrive:/mypath/etc/") ) and then don't reset it anyplace. Make sure you do NOT have setMediaPath anyplace else in executed code. Joel Uthe
Got it. Thanks alot!!

Question: Could someone clear up what the terms "double" and "floating point number" mean?

double and floating point numbers (float) are different types of primitive variables that can store decimal values. double is used the majority of the time. int is the other type of primitive variable that you know but it can't store decimals. Joel Uthe
- int x = 5/3; (x is now equal to 1)
- double y = 5.0/3.0; (y is now equal to 1.66667)

I keep getting the error "cannot find symbol; sumbol : constructor AdvancedPicture(java.lang.String)" and it marks the line

AdvancedPicture ap2 = new AdvancedPicture(FileChooser.getMediaPath("swan.jpg"));

What does it mean?

You need to create a constructor (a special method that initializes an object).
```
public AdvancedPicture(String s){super(s);}
```
Joel Uthe

When I use the getPixel(x,y).setColor(Color.green), it gives an error, saying that "Color" cannot be found.

You need to import the color class (you see the imports at the top of Picture.java?). Add the line import java.awt.Color; to the top of your file. Joel Uthe

Do we need to list our TAs as collaborators if we used the code they wrote in recitation as a big starting point for our homework?

It is a good idea to list them. Joel Uthe

Question: my for loop looks like this

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

and I keep getting the error "cannot find symbol variable length."

My guess it is a type and should be pixels.length not pixel.length. Joel Uthe

Question: I changed it, and now it says "cannot find symbol variable pixels". Ho hum...and it's the only error I have. It would suck if I got a bad grade because of something stupid like this.

You need to declare and initialize Pixels. Dawn Finney.

Question: What is a NullPointerException?

This occurs when a method is called on a variable that is pointing to null. Because null can be thought of as essentially "nothing" placeholder, calling a method on null is similar to asking "nothing" to do something which is just logically impossible and yields a NullPointerException. It usually has to do with poor initialization or bad assignment. Dawn Finney.

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Homeworks-Spring 2008 last edited on 14 April 2008 at 11:35 am by lawn-128-61-18-61.lawn.gatech.edu