Questions on HW5-Fall07

Questions on HW5-Fall07

Post your questions for HW5 here.

For the third method we have to write for the homework, is this the proper constructor? public void replaceWithModifications(PositionedSceneElement findelement, double[] types){

This is called a method header and is completely different from a constructor. Yes the method header looks to be correct. Dawn Finney.

Also, how do I traverse the array that is inputed? Right now I have: for (int i= 1; i<=types.getLength();i++) {. That, however, does not work because it says there is no getLength() method in the class double. How do I go about traversing the array? Thanks!

We have worked with arrays before and an inputted array is no different. The correct line is: for (int i= 0; i < types.length; i++) . Remember that Java is 0-indexed (indices start at 0) so you must start your for loop at 0. Dawn Finney

If I am working in the PositionedSceneElement class, how do I use the picture methods on the input nodes?

Each instance of PositionedSceneElement is a linked list node which is made up of data and a next. In this case the data is a Picture called myPic that you will have to modify. Be careful and remember to think about earlier in the semester where sometimes a method returned a new Picture instead of modifying the one you call the method on. Joel Uthe

Error: C:\cs1316\java-source\PositionedSceneElement.java:191: cannot find symbol
symbol : method negate()
location: class PositionedSceneElement

I don't know how to work around this. Even though the node will be a picture, I can't find it as a node and then edit it as a picture.

The PositionedSceneElement is just a box that holds two things (Picture myPic and PositionedSceneElement next). In order to preform an operation to change the picture (such as negate) you have to tell the box to give you the Picture and then change the picture. You can't just tell your computer to play music, you have to tell iTunes to play the music. So you tell the computer to get you iTunes and then tell iTunes to play music. In your case you have to tell PositionedSceneElement to give you the picture. Which method in PositionedSceneElement returns a Picture? Joel Uthe

For the replaceWithModification(findelement,int type), the instructions say to replace findelement with a new node. Instead, can we just replace findelement's myPic with a the modified Picture?

You could, but you will probably have to write a setPicture method in whatever node class you are using. Dawn Finney.

I am sorry, words don't do me good. This question wording is too complicated for me, in the final product, I am not sure what we're suppose to have shown. Three separate pictures what shows up at the same time or mayhaps something else?

When the TA runs your PictureTest class, 4 pictures need to show up (all at the same time is fine). The 1st is the original linked list and then one picture for each new method. It is my strong suggestion to go to office hours if you are still confused or you can im me online from now (3pm) until about 7:30pm (AIM: thelatterhalf, Skype: dawnshanti, just message me on skype don't call. My number isn't listed.). Dawn Finney.

Will oldelement/findelement ever be the last node in the list? If so, how can I manipulate the last element (b/c with "while current.getNext() != null", the loop breaks before changes to the last node can be made)?

Yes it can be equal to the last node. Your while condition really depends on if you are working on current or current.getNext() each time in your loop. Just modify the while loop's condition to suit your needs. Dawn Finney.

I have all of my code written including all of the methods in PositionSceneElement but only one of them works, The second,(replaceWithModification). The other two have the same error stemming from the same spot in our code, and the error is a null pointer exception in the drawMeOn method, called by drawFromMeOn, from the PositionedSceneElement. Somehow i think that the 'this' statement in that part of the code is being set to null when we locate the node we want to replace and try and replace it with another node(findAndReplaceRepeat method), or replace it with numerous modified nodes (replaceWithModifications method). I cannot find how or why we have a null pointer exception but i think that is the only error preventing me from finishing this assignment

This is a pretty common error that students have. You are correct on your analysis in that if you call this.drawFromMeOn() method where this==null, then it is (null).drawFromMeOn() which is illegal and will throw the NullPointerException that you are getting. So you need to think about when you set this. Because at some point you are setting something to null that should be. There is an error someplace in your code, not in the code that was provided to you. Joel Uthe

Do we have to show all 4 pics in 1 "world" or in 4 different "worlds" ?????

4 different Worlds. 4 new items will open up in the Windows Task Bar. Joel Uthe

When I run my PictureTest class, it shows all 4 windows. But the problem is that in my second method,it uses the modified linked list from the first method. So, in my third window, I don't see the original image modified but the second image already modified by the first method, modified again. How is that possible?

Redo the linking process. Redo whatever you did for the making the original image and then do your next operation on it. Joel Uthe

In total we need 1 picture in 4 different worlds, right? And that pic must be modify according to the hw, right?

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Homeworks-Fall 2007 last edited on 23 December 2007 at 7:08 pm by adsl-152-173-97.asm.bellsouth.net