array of rectangles exam question

[Jinny Morris]

Mr. Ritchie -

Sorry - thought it was pretty much the same question! So here's the new thread ... will add more when I have something working.

[Jinny Morris]

The question was:

"The question opens with a class of a rectangle
it has methods to set the dimensions
return the width height and area and print these out

the question is

a) Write a method that takes as a parameter an array of Rectangle objects and prints out the details of every rectangle stored in this array.

b) Write a method that takes as a parameter an array of Rectangle objects and returns an array of the areas of the rectangles stored in this array"

assumptions:

1. We don't have to construct the rectangles
2. The methods that return the height, width and area are called getHeight, getWidth and getArea respectively
3. I don't know whether there is one method which prints out all properties of a rectangle or separate methods to print out each property; since the question is easier to answer if there is already a method to print everything in an understandable way, I'm going to make that assumption - this (hypothetical) method will be called printRectangle.

So:

void printRectangleProperties (rectangles[])
{
   int i = 0;
   for (rect:rectangles)
   {
      System.out.print("for rectangle " + i + " " + rectangle[i].printRectangle);
      i++;
   }
}
 
double[] rectangleAreas (rectangles[])
{
   double[] areas = new double[rectangles.length];
   for (i = 0; i < rectangles.length; i++)
   {
      areas[i] = rectangle[i].getArea;
   }
}

Comments? hints? criticisms? (I'm learning Java from books and don't have a whole lot of "exercises" to practice on ...)

Thanks!


EDIT by mw: Added Code Tags.
[ May 30, 2007: Message edited by: marc weber ]

[marc weber]

That's a great way to learn! There are a few details that need to be worked out here. The best way is to complete the code with a Rectangle class and see how it really works.

One tip: When declaring a method argument list, you need to specify the type along with the variable name. For example, (Rectangle[] rectangles) where "Rectangle[]" is the type (an array of Rectangle references) and "rectangles" is the local variable referencing that array.
[ May 30, 2007: Message edited by: marc weber ]

[marc weber]

Originally posted by Jinny Morris:
Mr. Ritchie -

Sorry - thought it was pretty much the same question! So here's the new thread ... will add more when I have something working.

(For anyone wondering, this was prompted by this thread.)

[Jinny Morris]

Marc -

Thanks! I'll try that - so probably won't post again right away. No self-confidence ...

[Campbell Ritchie]

Sorry, I didn't realise you were asking about the same rectangles question. You have managed more than that other chap. You won't get your enhanced for loop (also called a for-each loop) to work like that. Look here, and use ctrl-F->"enhanced". You can miss out the bit about i and (as Marc Weber has already told you) put "Rectangle[] rectangles" as your parameters.

Good luck.

[Campbell Ritchie]

Only two changes needed for your "rectangleAreas" method. Apart from the change of the parameter to "Rectangle[] rectangles" which Marc Weber told you about, you need to insert a statement to return the array of areas.

Any method which has a return type must have a statement to return something of that type, and a method with "void" must not return anything at all.

[Jinny Morris]

Marc and Campbell -

Thank you both very much! Marc, thank you for the "prod"; I needed it. Campbell - thank you for the hints.

Having spent much too long plumbing the depths of my misunderstandings about object orientation, I finally have created something that works. Right. Yeeeee-HA!