Questions on HW1-Summer07

Questions on HW1-Summer07

Ask Questions on homework 1 here. Please enclose code with <code> </code> tags.

Question:How do I manipulate a picture?

Guess Professor Potts will explain everything in class tomorrow. Go ahead and set up Java and Dr. Java on your computer by following the directions at READ ME FIRST. Open the Picture.java in your java-sources folder. Click "Compile" near the top right of Dr. Java. It should compile without errors (warnings are fine!). If it doesn't then, you may have set up Dr. Java incorrectly. Reread the instructions on setting up or ask a TA or someone else in the class for help. If Picture.java compiles without errors, then you're good to go. Try the following lines in the Interactions Pane of Dr. Java: (You probably need to change the paths of the Pictures I'm referring to so that they reflect the locations of the pictures on your computer)
```
Picture p;
p = new Picture("C:/cs1316/MediaSources/swan.jpg");
p.show();
p.clearBlue();
p.show();
```
This above segment of code should show the original swan picture and the modified version with all its blue set to 0 for each pixel.

Now try:
```
p = new Picture("C:/cs1316/MediaSources/swan.jpg");
p.show();
p.lighten();
p.show();
```
Notice how we only changed the method being call on the Picture p.

So I have just shown you how to call the methods within the Picture class. Your job for Homework 1 to write your own Picture method or modify an existing method so that it does something different, because you cannot submit a method that does something a method in the Picture class already does. For a quick walk through on how to convert Matlab for loops and while loops to Java read Matlab to Java tutorial: for and while loops. Remember to change C:/cs1316/MediaSources/swan.jpg to reflect the location on your computer. Dawn Finney.

Question: where do we download the files that go in the classpath /cs1316/java-source ? Or are these files supposed to be built in to the SDK lib?

The java-source folder is found here. Just download this, unzip it, put it in the cs1316 folder you created, and then add it an extra classpath. These classes were specially written for this course so they are only available through the coweb or the textbook and CD combination at Engineer's. Dawn Finney.

Question: If we receive an error message that says "illegal start of expression", what exactly is this implying? THANKS!!!

It's likely you wrote your code outside of the class, in other words, after the last bracket closing the class. So just move everything above the last bracket. Dawn Finney.
Alternatively, you might have too many opening or closing parentheses at this point. In the editing pane, try clicking on a '(' or ')' on the line in question to see whether DrJava highlights the span of characters you intended Colin Potts.

Question: When I create a pixel array and then say..... pixel[index] - no matter which index it is, i get Red = 255, Green = 255, Blue = 255 ??? and the picture was not all the same color.

I'm afraid you're going to have to be more specific about your methods. It's likely that you're doing something incorrectly, because I can't really think of another occasion where that would happen. For free to explain more here or email me your code. Dawn Finney.
What picture are you referring to? When you create a new Picture, it will be white all over, which is what the values in your pixel array reflects Colin Potts.

Link to this Page

Homeworks-Summer 2007 last edited on 21 July 2007 at 10:06 am by adsl-154-122-133.asm.bellsouth.net