Questions on HW3-Spring07

Questions on HW3-Spring07

Question: Is our homework now due on Mondays at 10, or was that just the first assignment (so it's still due Friday at 7)?

Based off of the homeworks description page, I'd say the day of the week the homework is due varies from homework to homework, but are all due at 7pm EDT of the specified date. Homework 3 is due Monday Feb. 5. -Dawn
Dawn's right.-Mark Guzdial

Question: Where is the blockingplay() method? It is not in the Sound Samples.

The blockingPlay() method is in SimpleSound.java. Java is case-sensitive! Dawn Finney

Question: for this homework we are going to write long code something like
pete-turtle on world
pete.square(30); c4.blockingPlay(); pete.forward(100); e4.blockingPlay().....???

Sure that's one of the horrible ways of doing the homework, 'cause when I dance I always dance a little, stand still for a bit, listen to the music, and then dance some more. The homework requirements say it okay to dance like that. Of course there are other ways. Gotta ask me though. I'm not here to hand out answers but rather help you get to them. :P Dawn Finney

Question: Just to clarify, are sampled sounds the sounds that are in .wav files in our mediasources folder? If not, I am confused as to what sampled sounds are.

Uh yeah, I believe so. I do admit the wording in the homework is a bit strange. Dawn Finney
That's my fault – sorry. Yes, .wav files are sampled sounds. Mark Guzdial

Question: Can we use sound files other than the ones in the MedisaSources Folder??? I assume we do but I was not sure.

Yeah. Dawn Finney
Absolutely! In fact, here's a zip file full of different instruments playing different notes, for those who want to do songs but don't want to do MIDI. Mark Guzdial musicSounds.zip Just download this, expand it, and put the files in your MediaSources directory.

Question: When we are using midi, how do we write two notes playing at one time? For example, you need to write chords with piano music, and I would like for the chords to be played on one part, instead of having multiple parts with one note for each beat.

This sounds kind of like what you have to do for homework 4. I would check out structuring-music.ppt for good sample code and explanation. -Dawn Finney
As usual, Dawn (The Dawnster? Guru Dawn? Dawnerooni?) is right. The easiest way I know to do it, in JMusic, is to create three parts to the same score, with one note of the chord in each of the three parts at the same point in time. So, to play a C-major chord, play a C in one part, an E in the other, and a G in the third. There's some more description of how to do this in the book. Mark Guzdial

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Question: What happens if your computer can't run it b/c there is not enough memory?

This really shouldn't happen for this homework unless your sound file is enormous, even then, not really. I would delete the stuff in your computer's temp folder and try again. If it still occur consider trying on someone else's computer or using a different Sound. -Dawn Finney
Are you using .append? Here's my guess – you're adding up (appending) larger and larger sounds, and blowing up memory that way. This HW really doesn't need any use of append at all. Try doing without it and see what happens. Mark Guzdial
....Or, as shown in class today, perhaps you are linking your sounds in an infinite fashion where they continuously point to something else...-a fellow student :)

Question: Sometimes when I run my Turtle Dance, I get an error that says something like "Exception in thread...Concurrent Modification...". It doesn't happen all the time, which is weird. What is it?

That's an error that means that you are moving your turtles faster than Java can keep up. "Keep up" depends on how fast your computer is, how fast your graphics board is, how many applications you have running at once – seriously, it's a complicated matter. Your program will still run fine, but the screen won't actually show all the things that you're doing with the turtles. Don't worry about it – your TA may not even get that exception, and it doesn't actually prevent your program from running. (But it is kinda weird to get that error on this homework – either you're doing a WHOLE lot with your turtles, or your computer is slow or overloaded. Try closing a few applications.) Mark Guzdial
No, you won't get points off for it. Mark Guzdial

Question: Is there a way to make the background color of a world something other than white?

Maybe. I think the easiest way is to use a Picture that is one flat color for your background. -Dawn Finney
Yes, I think it's called setPicture. See the JavaDoc on World. Mark Guzdial

Question: For the hw, it says implement it in a main method. So I just wanted to clarify, is a main method something similar to what we did in hw 2 for example, we defined our class and then wrote:

static public void main()

I was just wondering if this is what defines a main method.

A main method is defined like so public static void main(String[]args). You should already know this...(cries) -Dawn Finney

Question: Why is Dawn answering all these questions when she should be busy at work?

(shrugs) -Dawn Finney
Because she's kind and knows this stuff well Mark Guzdial

Question: What are "the other ways" of making the turtle dance w/ music ?

I personally think that using append() to add all the sounds together and using FrameSequence to create the animation is the easiest way to go about this. Then you would play the big sound just using play and then play the FrameSequence. The music should play while the turtles are still moving, if I remember correctly. Oh a for loop (or two) will make your turtle animation easier and using something like Math.random() -Dawn Finney
I'm going to disagree with Dawn on this one. It's easiest to write onto the World and just (blocking)play a little, move a little. Mark Guzdial
Eh differing opinions, just goes to show there are many ways to solve a problem with CS. -Dawn Finney

Question: I can't remember, what is the way to get access to the table that shows all the notes and their respective JMC notation?

It should be in the textbook as one of the appendixes last I checked. -Dawn Finney
Yes. You can also look at the JMusic Java docs which list all of it. Mark Guzdial

Question: Do you want us to show the turtle, or is it enough to just drop a picture? Does the turtle have to be visible?

I would say yes the Turtles should be visible (how can you tell if the dancer is dancing if the dancer is invisible?), but because nothing in the grading criteria or the homework mention it, ultimately I think you need to ask your TA if it is acceptable to not have the Turtle visible. Though it is easy to make the Turtle visible (setVisible(), I think). -Dawn Finney
It's actually turtle.show(). You don't have to show the turtles, but it is easier, as Dawn says. Mark Guzdial
Yeah sorry didn't have time to look it up. -Dawn Finney

Question: Frame Sequence keeps giving me the following warning
File: C:\Documents and Settings\Leflor\My Documents\Programs\java-source-Fall06\FrameSequence.java [line: 161] Warning: C:\Documents and Settings\Leflor\My Documents\Programs\java-source-Fall06\FrameSequence.java:161: warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.List
And when I run my code a pointer is returned as null so it just stops running before it gets to play the video, I get frames no moving imagery in front of me though.

NullPointerException: 
  at FrameSequence.replay(FrameSequence.java:210)
  at turtleFrames.replayFrames(turtleFrames.java:100)
  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)

Don't worry about the warning too much right now. It won't affect your code. A NullPointerException typically occurs when you try to access something that is null. For instance:
```
String name; 
name.charAt(0);
```
will yield the same error, because you're trying to access a specific letter of the String name, but you have yet to define name as anything. Your NullPointerException occurs because you call FrameSequence's replay() method without adding any frames to FrameSequence. -Dawn Finney
My suspicion is that you're adding something to FrameSequence that is NOT a Picture. That's what the complaint is at compile time. Because you're trying to store something that's not a Picture, it doesn't actually get stored. Thus, when you try to play it, you get the error about a NullPointerException – Java is saying, "I've got a space here in the frame sequence for a picture, but nothing got stored here! It's null!" Mark Guzdial

Question: When I try to compile one of the example files like Song.java the very first line: import jm.music.data.; is highlighted. The error reads
Error: C:\Documents and Settings\Owner\Desktop\cs1316\java-source-Fall06\java-source-Fall06\Song.java:1: package jm.music.data does not exist
do i have to set a path or something?

You should have Dr. Java pointing to the JMusic folder like you have it pointing to the JavaSource and MediaSources folders. See if that helps. Dr. Java-> Edit-> Preferences->then add an extra classpath to JMusic. -Dawn Finney

but I already have a path to jmusic set up in preferences.

Is it pointing to the inst folder and jmusic.jar? -Dawn Finney

my jmusic.jar isn't actually inside the inst folder though. its right in the top layer of the jmusic folder. should the path be directly on the .jar file?

The path should point directly to the .jar and jmusic.jar is in the right place. It shouldn't be in the inst folder. -Dawn Finney

much obliged Dawn. it works now.

No prob. I can get back to my real job :P -Dawn Finney

Question: I've put my whole code in order and it looks right and compiles correctly and even runs, but the sound does not play in the place I put it in. I have a while loop so the turtles spin for a while and even though the sound is placed higher above the while loop the music still plays after. tell me why!

I think the big question is why a while loop? A for loop would be a much better choice. The problem could be the speed of your computer. As long as there is some weaving between the music and the movement of the turtles, it's fine. Better late, then never. -Dawn Finney

lol my problem is that the turtles don't show up, although I have the blank world come up. instead of doing Turtle.show(); which gives me an error message I did the names of my turtles: Jones.show(); etc...

I'm guessing this is more of a statement than a question. show() isn't a static method like setMediaPath() and getMediaPath(), thus you must declare an instance of Turtle
```
World world = new World(); 
Turtle t = new Turtle(world);
```
before you do
```
t.show();
```
-Dawn Finney

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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

Questions on HW3-Spring07

New Collaboration Policy REMOVEDPlease review: Collaboration Policy– Mark Guzdial

Link to this Page

New Collaboration Policy REMOVED
Please review: Collaboration Policy
– Mark Guzdial