Questions on HW2-Summer07

Questions on HW2-Summer07

Ask Questions on homework 2 here. Please enclose code with <code> </code> tags.

Question: The assignment says "Create a PictureCollege.java class with...", and I was curious if it was supposed to be PictureCollage.java

Hahahaha. Nice catch. My bad. Dawn Finney.

Question:If we want to use some of the picture manipulations used in the Picture.java class, can we import the class at the beginning of our code, and then call the methods in the methods we create within the PictureCollage.java class?

It isn't necessary to "import" Picture.java. You can use Picture methods as long as you have a Picture object. Look at MyTurtlePicture.java in your java sources folder for a good example. Dawn Finney.

Question: Is using only one type of image manipulation okay, as long as we have the original picture and at least three copies that are manipulated?

No, you need to do 3 DIFFERENT types of manipulation. Dawn Finney.

QuestionAre we still suppose to submit it on tsquare or through an email?

Submit on TSquare. If something goes wrong with submitting on TSquare, email your grading TA. Dawn Finney.

Question: I am getting this error when i try and use methods from picture.java even though i have declared everything thing to be a picture. what does void mean??

File: /Users/taylorvirgil/Desktop/Georgia Tech/CS 1316/java-source-Fall06/PictureCollage.java  [line: 21]
Error: incompatible types
found   : void
required: Picture

REMOVEDces are you're doing something like
```
Picture p = new Picture(FileChooser.getMediaPath("swan.jpg"));
p = p.decreaseRed();
```
A void method like decreaseRed() is a method does not return an object. Essentially you're telling Java that I want my variable p to be equal to nothing (not to be confused with null which is like an "empty" object). The Java compiler hates this and basically yells at you. A simple fix would be to change the second line to p.decreaseRed();. Dawn Finney.

Why am I getting this message:

NullPointerException: 
  at javax.swing.ImageIcon.loadImage(Unknown Source)
  at javax.swing.ImageIcon.setImage(Unknown Source)
  at PictureFrame.updateImage(PictureFrame.java:91)
  at PictureFrame.initFrame(PictureFrame.java:152)
  at PictureFrame.<init>(PictureFrame.java:57)
  at SimplePicture.show(SimplePicture.java:345)
  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)

why I try to show my collage? Everything compiles fine, and it should inherit the show method from Picture, so...?

A null pointer exception means that the variable's name doesn't correspond to an existing object. It generally happens because you are trying to do something with an object that you have declared (which is why if compiles ok) but not constructed or initialized correctly. Maybe one of your picture methods returns a Picture object but doesn't create or copy it correctly before returning. Colin Potts.
"It should inherit the show method from Picture." I'm really hoping that you just have your terminology a bit confused because you shouldn't be dealing with inheritance in this homework. Like Colin said you probably called show() on null Picture object. Asking nothing (null) to do something (show()) is counter intuitive. You just have to give the Picture varable a new Picture. Dawn Finney.

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