RE: Java Questions Again: What's So Great About Recursion

  • From: "Sina Bahram" <sbahram@xxxxxxxxx>
  • To: <programmingblind@xxxxxxxxxxxxx>
  • Date: Thu, 7 Apr 2011 15:35:09 -0400

Let's not confuse memory with stack space please.
 
Every time you have a recursive function call, you need another stack frame or 
function record popped on, and that stack has a
limited capacity. Whether it's 256 bytes for a small model, 4K for a medium, or 
large at 65K, it's still not that huge . now, I
think the stack model has been revamped in later versions of the kernel in 
Windows/Linux, but the point is it has nothing to do with
the fact that you have 4GB of ram versus 256MB of ram back in the day.
 
So yes, memory is cheap, but recursion depth still is very much excruciatingly 
small.
 
Take care,
Sina
 
From: programmingblind-bounce@xxxxxxxxxxxxx 
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Ken Perry
Sent: Thursday, April 07, 2011 2:12 PM
To: programmingblind@xxxxxxxxxxxxx
Subject: RE: Java Questions Again: What's So Great About Recursion
 
 
 
Tylor is correct that recursion is great on algorithms that deal with trees 
whether it is for sorting or searching or even writing
or reading them from or to disk.  
 
A couple more reasons for them.
 
1)      They can make rather large loops look really small and easy to upkeep 
at the cost of memory.  Note how cheap memory is now
days.
2)      Some things are just easier to do with recursion for example the 
knights tour problem is not so easy to do with loops
3)      Some weird languages don't have great looping structures and recursion 
can help you there.
 
Now if you're in for a good joke just search for "recursion" on google.  You 
will notice that the google programmers can be funny.
Google will ask you.  Did you mean recursion?  Then you click on that and guess 
what it asks if you mean "recursion"?  again. You
can click that all day long if you like.
 
Ken
 
From: programmingblind-bounce@xxxxxxxxxxxxx 
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Stanzel, Susan - 
Kansas
City, MO
Sent: Thursday, April 07, 2011 1:45 PM
To: programmingblind@xxxxxxxxxxxxx
Subject: RE: Java Questions Again: What's So Great About Recursion
 
Hi Listers,
 
I have asked the Java teacher to enlighten me on this subject of recursion. I 
have wondered what it was for also, but it was just
one of those things I didn't bother to ask.
 
Susie
 
From: programmingblind-bounce@xxxxxxxxxxxxx 
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Stanzel, Susan - 
Kansas
City, MO
Sent: Thursday, April 07, 2011 12:32 PM
To: programmingblind@xxxxxxxxxxxxx
Subject: RE: Java Questions Again: What's So Great About Recursion
 
Hi Listers,
 
Java has a serialization mechanism to do that kind of tracking.
 
Susie
 
From: programmingblind-bounce@xxxxxxxxxxxxx 
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Homme, James
Sent: Thursday, April 07, 2011 12:16 PM
To: programmingblind@xxxxxxxxxxxxx
Subject: RE: Java Questions Again: What's So Great About Recursion
 
Hi Ty,
Is it done when it has finished reading the file?
 
Thanks.
 
Jim
 
Jim Homme,
Usability Services,
Phone: 412-544-1810. Skype: jim.homme
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From: programmingblind-bounce@xxxxxxxxxxxxx 
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Littlefield, Tyler
Sent: Thursday, April 07, 2011 12:59 PM
To: programmingblind@xxxxxxxxxxxxx
Subject: Re: Java Questions Again: What's So Great About Recursion
 
Jim:
Recursion has a limited number of applications where it is actually more useful 
than a loop, I'll give one I use it for.
In my game engine, properties are stored in a tree setup with a root property 
and all other properties work from there. so, you
could essentially have stats.health, stats.mana, etc. stats is the root node, 
health are the children nodes on stats.
Now, here's where recursion comes in handy.
when I serialize this tree, I write it all in xml. so I'll serialize the stats, 
then I'll serialize health. what I do is something
like this:
Serialize(XMLNode, property)
so lets say that stats.health has two properties: stats.health.hp, and 
stats.health.max_hp. in order to serialize that I would have
to loop through the properties of stats.health, then if hp were to have another 
property I'd have to loop through those, which could
get messy.
Rather than do that though, I use recursion. so the serialization setup calls 
serialize on stats, passing the root, then that
function calls serialize on stats.health passing health.
I hope I explained that properly. Essentially in summary, it allows me to keep 
passing in each node of the tree until I am finally
done. I can recurse until I get done serializing a branch, at which point I 
will pop back to where i was because the recursion will
return when it's done.

On 4/7/2011 10:51 AM, Homme, James wrote: 
Hi, 
It's probably my ignorance coming out to bite me again, but I just was reading 
about recursion in my Java book and thinking that it
isn't all that useful because you can do the same stuff with a loop. Maybe the 
book examples are so simple that I just don't see
it's usefulness. They were even saying that recursion eats up more memory than 
loops do, so I'm wondering why I learned it in the
first place, other than to know how it works and that it exists. 
  
Please help. 
  
Thanks. 
  
Jim 
  
Jim Homme, 
Usability Services, 
Phone: 412-544-1810. Skype: jim.homme 
Highmark recipients,  Read my accessibility blog 
<http://mysites.highmark.com/personal/lidikki/Blog/default.aspx> . Discuss
accessibility here 
<http://collaborate.highmark.com/COP/technical/accessibility/default.aspx> . 
Accessibility Wiki: Breaking news
and accessibility advice 
<http://collaborate.highmark.com/COP/technical/accessibility/Accessibility%20Wiki/Forms/AllPages.aspx>
  
  

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-- 
 
Thanks,
Ty

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