Questions on HW5-Spring07

Questions on HW5-Spring07

Question: So, in this hw, we have to create all three methods from the scratch right?

Yup. If you find code like remove() or last() or repeatInserting() useful, you can always chop pieces out, but overall, they're brand new things. Mark Guzdial.

Guzdial is the man

Question: Are we going to make these new methods in PositionedSceneElement.java, if not, where should we make them? I know we are going to use them in our PictureTest class.

Yes, you can put the new methods in PositionedSceneElement.java. Dawn Finney.
In fact, you can use any of the picture linked list classes: PositionedSceneElement, LayeredSceneElement, or SceneElement (which automatically makes them available, via inheritance, for SceneElementPositioned and SceneElementLayered). It's your choice, and it doesn't matter to the TA's since your PictureTest class will use the one you modified (right?). Mark Guzdial
I would highly recommend using PositionedSceneElement. It's more straightforward than SceneElement and its child classes. It's also easier to see if your linked list is working correctly, because Pictures are displayed side-by-side instead of one on top of the other. Dawn Finney.

Question: Looking at the instructions for the homework, the lines...
"firstpictureinlist.findAndReplaceRepeat(oldelement,newelement,n) Find oldelement (it's a node, not a picture,... blah"
"firstnodeinlist.replaceWithModification(findelement,int type) Find the node findelement (a node, not a picture,...blah"
"firstnodeinlist.replaceWithModifications(findelement,double[] types) Find the node findelement (a node,... blah"

Are the classes "firstpictureinlist" and "firstnodeinlist" simply made up to explain that findAndReplaceRepeat and replaceWithModification and replaceWithModifications are methods?

"Using any of the linked lists of pictures that we created (where ordering represented linearity, or layering, or using turtles to walk the list), implement three additional methods (where firstpicturenodeinlist is a node, not actually a picture)," from homework 5 description.

I think:
```
firstpictureinlist.findAndReplaceRepeat(oldelement,newelement,n)
firstnodeinlist.replaceWithModification(findelement,int type)
firstnodeinlist.replaceWithModifications(findelement,double[] types)
```
are actually supposed to be:
```
firstpicturenodeinlist.findAndReplaceRepeat(oldelement,newelement,n)
firstpicturenodeinlist.replaceWithModification(findelement,int type)
firstpicturenodeinlist.replaceWithModifications(findelement,double[] types)
```
I'll check on that.

firstpicturenodeinlist is basically an example of an instance of a picture linked list class not a class itself and its name describes its characteristics. Simply put all 3 methods will be called on the first node (head) of a picture linked list. Dawn Finney
Dawn's awesome and that typo is fixed - Joel Uthe
Ditto! Mark Guzdial

Question: PositionScenedElement is a node in itself right? just wanted clarification.

Yes. PositionedSceneElement is a node itself. Remember that you create a linked list by linking nodes together. Dawn Finney.

Question: For our first method, is it okay to assume that n is greater than equal to one?

In this case I think it's safe to assume that n should be greater than 0, but what if, just what if, the user puts in 0 or -1. I personally would just place a little if statement into my code to catch these mistakes by the user. The best way to go about writing a method is to imagine the user (of this method) as a rather inexperienced person and prone to mistakes, a n00b to the CS world, if you will. If you can consider and handle all possible input from the user, the less likely your program is going to crash due to user error. So something like:
```
//if n is less than 1, then print statement and return
if (n < 1){
  //prints out "n needs to be at least one. Good job genius!"
  System.out.println("n needs to be at least one. Good job genius!");
  //exits method
  return;
}
```
But whether it is required to catch these possible user mistakes is something you would have to ask your TA. Dawn Finney
You can presume that n will be at least 1, and it won't be a requirement to check for n = 0. But Dawn's right – it's better to be safe than sorry. Mark Guzdial

Question: Considering the code for methods 2 and 3 (I'm writing my methods in SceneElement) This class doesn't know the methods negate, mirrorVertical, mirrorHorizontal, and makeSunset does it? So do I have to copy and paste these methods (from Picture) into this class in order to be able to use them here?

Even if I do copy and past those methods into the SceneElement class... would I be able to say something like (one of my inputs for method two is "SceneElement oldelement") oldelement.negate(); ??

Or am I just way off base?

You're way off. You have to think about what is getting manipulated here. The node...or perhaps the data it holds, a Picture? Surely this data, a Picture, is capable of using Picture methods. Dawn Finney

Question: I'm a bit confused...On pg. 160 in the course notes, it says that SceneElementPositioned will have an x and y for positioned, but SceneElementLayered will not. However, it's SceneElementLayered that has x and y variables. Am I looking at this wrong or is something incorrect?

I think the textbook is incorrect. SceneElementLayered needs a x and y position, because it places Pictures one over the other while SceneElementPositioned doesn't need an x and y position because the Pictures are placed next to each other. But this statement would still need Professor Guzdial's seal of approval. Until then, it's just in my opinion. Dawn Finney.

Question: To access a picture of a node called node1 do we type node1.myPic ? Also suppose we have a picture p and want to set it to the picture that node1 contains do I type p = node1.myPic ?

getPicture() returns the node's picture in the classes Professor Guzdial listed above. Feel free to actually look at the methods in the class or the javadoc before you ask on the coweb. Dawn Finney.

Question: "Using any of the linked lists of pictures that we created (where ordering represented linearity, or layering, or using turtles to walk the list), implement three additional methods (where firstpicturnodeinlist is a node, not actually a picture)"
– where are these linked lists of pictures that we have created?

See the second question from the top. The classes are found in your java-sources folder like every other class in this course. Dawn Finney.

Question: public void replaceWithModification( PositionedSceneElement findelement, int type)

When I type this line in, these are the errors I get:
9 errors found:

File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 205]
Error: C:\cs1316\java-source\PositionedSceneElement.java:205: class, interface, or enum expected
File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 207]
Error: C:\cs1316\java-source\PositionedSceneElement.java:207: class, interface, or enum expected
File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 212]
Error: C:\cs1316\java-source\PositionedSceneElement.java:212: class, interface, or enum expected
File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 216]
Error: C:\cs1316\java-source\PositionedSceneElement.java:216: class, interface, or enum expected
File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 217]
Error: C:\cs1316\java-source\PositionedSceneElement.java:217: class, interface, or enum expected
File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 220]
Error: C:\cs1316\java-source\PositionedSceneElement.java:220: class, interface, or enum expected
File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 222]
Error: C:\cs1316\java-source\PositionedSceneElement.java:222: class, interface, or enum expected
File: C:\cs1316\java-source\PositionedSceneElement.java  [line: 224]

What do you think is wrong? I'm kind of confused.

Did you put the method outside of the class definition? Dawn Finney.

Question: Why does Dawn do all the work?

(shrugs). Dawn Finney.

Question: In part a, is newElement also a node? or is it a picture?

newelement is a node. Dawn Finney.

Question: On part a, if n was 0, would the function just delete oldelement?

Check out the 5th question from the top. Dawn Finney.

Question: i think the double in method 3 is supposed to be int. that's what one of the ta's said.

I think so as well, but it really doesn't matter too much. Since it's so close to deadline time I don't see a point in changing it. Unless the homework description is changed, please use double. Dawn Finney

Question: For our PictureTest class, we show a background with the original pictures, and then we show new backgrounds showing the pictures after they have been modified. My question is: Should each method modify the original linked list, or should they just modify the result of the previous method? In other words, after we do findAndReplaceRepeat, do we do a replaceWithModification on the result of that or do we go back to the original linked list?

Do whatever you think is best. Here's where comments come in handy. You can explain what is happening in the list in the comments. Dawn Finney.
Just keep tacking on – modify the same linked list. That's easiest and works fine. Mark Guzdial

Question: When I run my PictureTest, why do I get the following:

java PictureTest
ArrayIndexOutOfBoundsException: Coordinate out of bounds!
  at sun.awt.image.ByteInterleavedRaster.getDataElements(Unknown Source)
  at java.awt.image.BufferedImage.getRGB(Unknown Source)
  at SimplePicture.getBasicPixel(SimplePicture.java:270)
  at Pixel.getAlpha(Pixel.java:71)
  at Pixel.setColor(Pixel.java:211)
  at Picture.bluescreen(Picture.java:2220)
  at PositionedSceneElement.drawMeOn(PositionedSceneElement.java:78)
  at PositionedSceneElement.drawFromMeOn(PositionedSceneElement.java:63)
  at PictureTest.main(PictureTest.java:17)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
  at java.lang.reflect.Method.invoke(Unknown Source)

I remember getting this error last semester. I think the problem was that the background picture you are drawing is too small or the pictures in the list were too big. So I suggest making your background bigger. If that doesn't work try smaller pictures in the list. And if that doesn't work then you can email me, and we can try to figure it out. Dawn Finney.

Question: with replaceWithModifications(PositionedSceneElement findelement, double [] types), when i try to test my method i use replaceWithModifications( fly, {1,2,3}) i get a syntax error for using {, what am i suppose to use?

You need to declare the array: double[] array = {1,2,3}; and then do: replaceWithModifications(fly, array);. Dawn Finney.
Thanks, Dawn, for getting to so many of these questions!! Mark Guzdial

Question: are we supposed to hardcode the pictures in?

What does that mean exactly? Dawn Finney

I mean are we specifying the pictures inside the code or are we going to type them in interactions pane?

The first one and inside PictureTest.java. Dawn Finney.

Question: are these three methods we are making similar in structure to remove() or repeatInserting()?

Yes looking at these methods might help you, but whether the structure is similar or not is a strange question to ask. Dawn Finney.

Question: Say my REMOVEDked List is Tree1>Dog1>Tree2>Dog2. When I run:

–findAndReplaceRepeat(dog, house, 2): Does it need to replace both dogs with 2 houses, or just the first one?
–replaceWithModification(dog, 1): Does it need to negate both dogs or just the first one?
–replaceWithModifications(dog, {1,2}): When it's done, should both dogs be replaced with a negated and mirrored dog, or should the first dog be the only one changed?

You're not looking for a specific picture, you're looking for a specific node. Thus you would not be looking for dog (a picture) but instead dog1 (a node) or dog2 (a node). Dawn Finney.

Question: In the interactions panel I entered this command:
FileChooser.getMediaPath("tree-blue.jpg"), and it returned the proper path which was "D:/cs1316/mediasources/tree-blue.jpg"

Two seconds later I simply ran my PictureTest main method, and it gave me an error message saying that it couldn't load "nulltree-blue.jpg". So to see what was wrong I re-entered the same FileChooser.getMediaPath("tree-blue.jpg") in the interactions panel and it did this:

> FileChooser.getMediaPath("tree-blue.jpg")
"nulltree-blue.jpg"

meaning that it can no longer find the path to the file.
I re did the whole process from the beginning and got the exact same results. If I do the FileChooser.getMediaPath("tree-blue.jpg") in the interactions panel before I run my PictureTest main method, it works just fine. If I run the PictureTest main method and then try, it tells me the path is "nulltree-blue.jpg".

why do bad things happen to good people?

I have several suggestions:
- This maybe be obvious, but are you resetting the media path to null anywhere in PictureTest?
- Did you delete a text file called SimplePictureProperties? It gets created when you first use FileChooser.setMediaPath() and saves the media path in there. Deleting this file kills the media path.
- If you still can't figure it out. Set the media path in your PictureTest for your own testing purposes and then remove it or comment it out. Include in the comments on PictureTest, this description of the strange occurrence and tell your TA to watch out for it...
- Bad things happen to everyone, but not everyone whines about it. Dawn Finney.

Question When I try to retrieve the picture file from the PositionedSceneElement findelement, I get this error.

public void replaceWithModification(PositionedSceneElement findelement, int type) {
      
PositionedSceneElement current = this;
if (current == findelement);  {
        Picture p = getPicture(findelement);

Error: C:\Documents and Settings\Owner\My Documents\GT\Spring 2007\CS 1316\java-source-Fall06\PositionedSceneElement.java:175: getPicture() in PositionedSceneElement cannot be applied to (PositionedSceneElement)

I thought PositionedSceneElement is a node, and has the properties of a node such as getPicture()....?

The methods are called on objects by the way of a . operator. You're trying to call the method like this getPicture(findelement) when it should really be findelement.getPicture(). The Java compiler is actually freaking out because the getPicture() method doesn't take in any parameters. Dawn Finney.

Question: In replaceWithModifications, I have 4 if statements to change the picture, and then I define the new picture (actually I've defined it as a PositionedSceneElement) as p (PositionedSceneElement p = new PositionedSceneElement(oldelement.getPicture().....etc). But, when I try to put this new node back into my linked list, 'current.insertAfter(p)' I get an error saying cannot find symbol variable p in PositionedSceneElement. Why won't it recognize what p is??

I guess it really depends on if p is declared within a loop or not. Variables declared in a loop will be killed upon termination of that loop. For example:
```
int counter = 5;
for (int i = 0; i < counter; i++){
   if (i == 3){
     String s = "number 3";
   }
}//end of loop
```
After we hit the end of the loop, the only variable available to us is counter who was declared before the loop. I'm guessing that this situation is something like your case. So how do we fix this? It's actually quite easy to "save" s from deletion or garbage collection.
```
int counter = 5;
String s;
for (int i = 0; i < counter; i++){
   if (i == 3){
     s = "number 3";
   }
}//end of loop
```
Feel free to try this code in the interactions pane if you don't believe me. Just try accessing s (just type s and press enter) after each version. Dawn Finney.

Question: What is the method in the class double to find the length of an array of doubles? Am I asking the right question? If not, is the right question, is there a class array that knows is length? I think the second question is way off but I'm confused on the array of doubles that we have in replaceWithModifications().

length will give you the length of the array regardless of what objects it contains. So just do something like: array.length. No parenthesis necessary! It's not a method. Dawn Finney.

Question My picture test is taking a superrrr long time to run my three methods. Should it take a really long time or is there something wrong with my methods?

Sounds like an infinite loop to me. Check your loops. Dawn Finney

Question: In the homework question it says that our class PictureTest needs to show a "background" with the pictures on it. Does it have to be a background or can it just be a white background (one that you get when you create a picture like Picture bg=new Picture(1000,500);

White is fine. Dawn Finney

Question: Some of the pictures that I used for my PictureTest class look choppy(some parts missing or white where it should not be). Is this because they are not pictures like the tree.jpeg in our Mediasources, which is a blue chromakey picture. Is it ok if our pictures look like that???

If it is truly a concern of yours just change the pictures. I think as long as the TA can see the original picture and its manipulated version and can tell the difference. I don't believe it's a big deal. Dawn Finney

Hey Dawn,
Thanks a lot for your help.

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Homeworks-Spring 2007 last edited on 19 April 2007 at 10:45 pm by c-76-17-114-206.hsd1.ga.comcast.net