Questions on HW0-Spring08

Questions on HW0-Spring08

Ask questions on homework 0 below.

Question: I ran this line of code:

  FileChooser.setMediaPath("C:/CS1316/mediasources/");

but made a typo on the path, so that when i ran:

  Picture p = new Picture(FileChooser.getMediaPath("swan.jpg"));
  p.show();

I got an error. I went back and fixed the typo and then got the following error:

Error: Redefinition of 'p'

I tried using "clear" (as in, clearing the variables in MATLAB) but that doesn't seem to be a valid command in Java, so I closed DrJava and then started it again. That worked, but I'm sure there is an easier/right way to do it when something like that happens. Anyone know?

You are getting the error because you don't have to include Picture p again. p already knows it is a Picture and can just say > p = new Picture. Or you can either reset the interactions pane or recompile to reset the variables. Joel Uthe
"clear" doesn't exist in Java by the way. Like REMOVEDel said recompile the file or reset the interactions pane. Dawn Finney.

Question: I keep getting an error: "No compiler is available." I've tried several things and nothing seems to work.

Follow the instructions for Setting Up Java and pay special attention to the part where you are setting up the JDK. Dawn Finney.

Question: How do we save the stuff we typed in the interactions pane to turn in for homework?

You don't have to turn in the stuff that was typed in the interactions pane. You only need to turn in the simple first class HW0.java that prints "I have just written my first class!"
Be sure to turn in the HW0.java file and NOT the HW0.class (compiled with no source code) nor the HW0.java~(the tilda means it is a temp file). Joel Uthe

Question: I have followed exact codings on HW0, but Java keeps telling me "class, interface, or enum expected"

This means that your code is not contained within a class such as:
```
  public class HW0{
    //code here
  }
```
Keep in mind that everything before "CREATING YOUR FIRST CLASS" is supposed to be done inside the Interactions Pane without resetting from the beginning to the end of the instructions. Dawn Finney.

Question: Where exactly on TSquare are we supposed to submit the assignment?

It isn't up yet. We are still in the process of setting up T-square access for TAs so stay posted. Joel Uthe

Question: A quick question on formatting code - the code for hwk 0 is indented and is nice and pretty (the actual assignment, that is), but I'm not sure the quick way to do that kind of formatting (the tab button doesn't seem to do too much). I can move it around with spaces and backspaces but I'm sure there's a better way. What is the proper way to lay out code? Also, I just realized I probably sent you a half a dozen emails. Sorry TAs, my bad.

I was wondering why I had 6 emails in my inbox. If you are talking about indenting in Dr. Java, the tab is the right way to go. Dr. Java will auto-indent for you. Highlight all the code you want indented and hit tab. For indenting on the coweb, you're sort of doomed to use
```
&nbsp;
```
which is the space character for html. If you enclose code with <code> </code> tags on the coweb, it will preserve the indentations of the code you copy from Dr. Java. Dawn Finney.

Question: I'm having trouble installing Dr Java on my Mac. I downloaded all the files and I can see the icon, but can't get it to start. Is there another application, similar to Dr Java, that I can use?

A lot of students have been having this problem. We think using an old version of Dr. Java for Mac will help, and we are trying to track down a version to post on the coweb. As for other applications like Dr. Java, which are called IDEs, you can check out this page: Additional IDEs. I also recommend JGrasp or JCreator. JGrasp should be available on all Georgia Tech machines. I know it is on the library and College of Computing machines. Dawn Finney.

Question: When I try to run the line of code (after defining the integers a and b) " int sum = a + b;" I get an error message: [error: redefinition of "sum"] ?

You probably already did int sum ... somewhere previous to that line. Just do sum = a + b;. Dawn Finney.

Okay, everything ran fine until I tried to compile FileChooser.java and Picture.java. It says there is no associated file, and then something about no compiler. I don't have to re-install everything, do I?

Did the initial System.out.println(..) and simple addition work? If it did then your compiler should be fine. If not, you may need to reinstall it. Did you open up the files and view the actual source code before compiling/trying to use them? Your linking may be setup incorrectly, or you may need to re-download the files. Joel Uthe

The simple addition and all that worked fine. When you say "open up the files and view the actual source code" do you mean the stuff that comes up in the big window on the right?

Yes, when you open the file, either by clicking on the open button or going to file open. And then the code shows up in the big window on the right. It has
```
public class FileChooser
```
someplace in it. Joel Uthe

Yep, the code shows up on the right. How do you know if the files compiled? I had tried setting the media path before and it gave me the error "undefined class 'FileChooser'" and brought up a window called "auto import class."

I have Dr. Java installed and running, but I am having problems compiling the files. How do I do that? Thanks.

It is important to compile the classes before you start using them. You can do this by opening the files that you will use and hitting the compile button. Or you can go though menus and go to Tools>Compile All Documents. It will probably come up with a message such as files compiled succesfully. Sometimes it comes up with errors (meaning it didn't compile) or warnings (warnings are fine, it is only because it was written in a previous version of Java). Joel Uthe

Help. What do I turn in for this homework? Do I have to or will you not be grading it?

Once T-square comes up then there will be a place for you to turn in your HW. You should be turning in HW0.java (not HW0.java~ or HW0.class). It is just the simple file that prints one line. We will not be awarding points for it, but we may look to see if you turned it in, especially if you have any t-square problems later. I'd be a good idea to turn it in just to be safe. Joel Uthe

Also, when I type 'int a = 6' and then try to add them, it doesn't show me any result or answer in the window. Where am I supposed to look? It is not giving me an error either, so I don't know what is wrong.

That piece of code doesn't specifically do anything but assign 6 to a, so there is no output. If your println's are working then you have correctly installed the JDK. Joel Uthe

Ok, I hope people are still asking questions on here. When I try to compile, I get the error saying it cannot read zip file entry. I'm sure that I'm not trying to read a zip file.

You probably forgot to extract the files from the archive before using them. We included the files in .zip format to allow a smaller download size. Some students have also forgotten to transfer the files off the cd and onto their computer before compiling. This doesn't work because when you compile, java creates another file that it puts next to the original which isn't allowed on a write-only cd. Joel Uthe

That's what I'm saying. I did extract them. That's why I don't understand the problem. Also, with the picture.java, when I hit compile it opens PictureExplorer.java, SimpleSound.java, and SoundExplorer. java and gives me a whole bunch of warnings.

Don't worry about the warnings. You probably have the classpaths pointing to the zipped folders. Go and change them so that the classpaths point to the extracted folders. Dawn Finney.

Link to this Page

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