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OOP and double loops

Started by Lode Feb 17, 2005 at 3:40 PM 56 replies 3.7k views

Original Post

Feb 17, 2005 at 3:40 PM

So I have this course "Information and Program Structures" and it's basicly another one of those courses involving Java and OOP, and with one of those Extremely Hardcore Object Oriented Programming professors. So he said: "A double loop is UNREADABLE! you make a seperate class for the outside and inside loop". In other words, he finds this unreadable:


for(int x = 0; x < width; x++)
for(int y = 0; y < height; y++)
{
    drawPixel(x, y, image[x][y]);
}

and wants instead to see two classes: one for the first loop, and one for the second loop!!! WTF is up with that? Has anyone ever heard that a double loop is unacceptable in OOP and should be split into two different classes? Can you imagine how FREAKING SLOW this would be for the inner loop? That would make OOP programs 100 times slower than non OOP ones, and that certainly isn't the case! OOP professers FRUSTRATE THE HELL OUT OF ME.

Samith

Feb 17, 2005 at 3:43 PM

I'm not even sure how you would make a whole new class just for a loop. I don't know Java either, though, so that might be why I have no idea what your professor is talking about.

I don't see anything wrong with a double loop though, I use them all the time in C++.

smart_idiot

Feb 17, 2005 at 3:44 PM

Your teacher is an idiot, but you'd better do as he says anyway so you don't fail.

owl

Feb 17, 2005 at 3:50 PM

make the two damn classes for him, tell him how great he is, and never ever do that again.

Trap

Feb 17, 2005 at 3:53 PM

In theory there doesn't have to be any performance difference between using procedural code and using classes. In practice it depends on the programming language and it's implementation.

In general it is a good idea to look at double loops to find stuff that should be classes, but in this case it is horrible overengineering.

smart_idiot

Feb 17, 2005 at 3:59 PM

for(int x = 0, y = 0; y < height; ++x == width ? ++y, x = 0 : 0) drawPixel(x, y, image[x][y]);

Well, it works in C++. There we go, one simple readable line of code. Sort of. Well not at all, but it's only one loop so why should he complain?

Raduprv

Feb 17, 2005 at 4:01 PM

LOL
That teacher IS an idiot. I usually try to not have more than 2 nested loops, but sometiems I have 3, maybe even nested with IFs. If the code is alligned properly, and commented, then I don't think anyone would have problems reading it.

nprz

Feb 17, 2005 at 4:03 PM

Quote:
Original post by Lode
So I have this course "Information and Program Structures" and it's basicly another one of those courses involving Java and OOP, and with one of those Extremely Hardcore Object Oriented Programming professors.

So he said: "A double loop is UNREADABLE! you make a seperate class for the outside and inside loop".

In other words, he finds this unreadable:
for(int x = 0; x < width; x++)for(int y = 0; y < height; y++){    drawPixel(x, y, image[x][y]);}
and wants instead to see two classes: one for the first loop, and one for the second loop!!!

WTF is up with that? Has anyone ever heard that a double loop is unacceptable in OOP and should be split into two different classes? Can you imagine how FREAKING SLOW this would be for the inner loop? That would make OOP programs 100 times slower than non OOP ones, and that certainly isn't the case!

OOP professers FRUSTRATE THE HELL OUT OF ME.

You should make it more confusing and get rid of the inner loop and just have one big loop.
like

for (int i + 0; i < width * height; ++i)     drawPixel(i % width, (i * width) + height, image[i % width][i * width + height]);

There might be a bad calculation, but basically you can make it the same iterations as two loops but write it correctly with one.

-edit- jesus smart_idiot, that code is hard to read :)

Evil Steve

Feb 17, 2005 at 4:04 PM

I think this is *slightly* unreadable:

for(int x = 0; x < width; x++)for(int y = 0; y < height; y++){    drawPixel(x, y, image[x][y]);}

But this is fine:

for(int x = 0; x < width; x++)   for(int y = 0; y < height; y++)   {       drawPixel(x, y, image[x][y]);   }

Or, better, this:

for(int x = 0; x < width; x++){   for(int y = 0; y < height; y++)   {       drawPixel(x, y, image[x][y]);   }}

But there's no freaking way I'd ever use a class for the inner loop, unless the loop was more than 3 levels deep, or it made sense to do it that way anyway.

Coward

Feb 17, 2005 at 4:05 PM

Quote:
Original post by smart_idiot
for(int x = 0, y = 0; y < height; ++x == width ? ++y, x = 0 : 0) drawPixel(x, y, image[x][y]);

I'm seeing and I'm liking..

smart_idiot

Feb 17, 2005 at 4:08 PM

I think you want i%width for x and i/width for y, nprz.

Now that I think of it, I think I could have used ++x == width && (++y, x = 0) and short circuit evaluation would have made it to the Right Thing™.

Nemesis2k2

Feb 17, 2005 at 4:09 PM

Quote:
I'm seing and I'm liking..

Really? When I look at that code, it makes me want to retreat into a small dark corner and sob. Maybe that's just a flashback to my childhood.

Trap

Feb 17, 2005 at 4:10 PM

Whats so bad about image.draw() calling line.draw() calling pixel.draw()?

As stupid as your prof may explain it to you, there might be a reason behind doing so.

Evil Steve

Feb 17, 2005 at 4:15 PM

Quote:
Original post by Trap
Whats so bad about image.draw() calling line.draw() calling pixel.draw()?

As stupid as your prof may explain it to you, there might be a reason behind doing so.

I also like my programs to run as slow as possible :P. Actually, I don't have anything constructive to add.

Raduprv

Feb 17, 2005 at 4:15 PM

Quote:
Original post by Trap
Whats so bad about image.draw() calling line.draw() calling pixel.draw()?

As stupid as your prof may explain it to you, there might be a reason behind doing so.

Because then you'd have 10 billion classes in your program, and it would take 2 days to compile.

Coward

Feb 17, 2005 at 4:17 PM

Quote:
Original post by Trap
Whats so bad about image.draw() calling line.draw() calling pixel.draw()?

It just seems ilogical to me..

When I think "image" I think a 2 dimensionel array of pixels. Not an array of lines.

smart_idiot

Feb 17, 2005 at 4:19 PM

for(int y = 0; y < height; y++) for(int x = 0; x < width; x++)

might be easier on the cache than

for(int x = 0; x < width; x++) for(int y = 0; y < height; y++)

Raduprv

Feb 17, 2005 at 4:24 PM

Quote:
Original post by smart_idiot
for(int y = 0; y < height; y++) for(int x = 0; x < width; x++)

might be easier on the cache than

for(int x = 0; x < width; x++) for(int y = 0; y < height; y++)

Indeed. It can be orders of magnitude faster to do it in the proper way, else you get huge cache penalties if the width is big.

darookie

Feb 17, 2005 at 4:27 PM

Quote:
Original post by Coward
Quote:
Original post by Trap
Whats so bad about image.draw() calling line.draw() calling pixel.draw()?

It just seems ilogical to me..

When I think "image" I think a 2 dimensionel array of pixels. Not an array of lines.

Nah! That's not an argument at all - image → array of scanlines, scanline → array of pixels; at least that's how my monitor 'sees' an image (ok, actually not, but sort of [smile]).

Trap

Feb 17, 2005 at 4:28 PM

Quote:
Original post by Coward
When I think "image" I think a 2 dimensionel array of pixels. Not an array of lines.

Valid point in this case.

Still you have a lot of assumptions and unnecessary overspecification in this code. 1. You assume the image is loaded into a 2d-array, 2. You assume it to be rectangular, 3. You specify an order in which the pixels are drawn which is completely unnecessary.

image.draw() is way better. All this bad stuff is then contained into a single place where you can easily change it.

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