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

  • From: "Homme, James" <james.homme@xxxxxxxxxxxx>
  • To: "programmingblind@xxxxxxxxxxxxx" <programmingblind@xxxxxxxxxxxxx>
  • Date: Thu, 7 Apr 2011 14:17:45 -0400

Hi Ken,
I see what you mean about the knight's Tour. That's a good one.

Jim

Jim Homme,
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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
Highmark recipients,  Read my accessibility 
blog<http://mysites.highmark.com/personal/lidikki/Blog/default.aspx>. Discuss 
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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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