[program-java] Re: Java: Redimensioning my existing array.

  • From: Steve Meacham <program-java@xxxxxxxxxxxxxxx>
  • To: program-java@xxxxxxxxxxxxx
  • Date: Fri, 3 Sep 2010 12:33:18 -0500

If you're allowed to, what exactly is this data structure supposed to
represent/do?

On Fri, Sep 3, 2010 at 12:21 PM, Corbett, James <James.Corbett@xxxxxxxxxxxxx
> wrote:

> Steve:
>
> I ended up with creating a class that contains the three values:
>
> Pseudo code....
>
> Class LineAmount {
>
> String province;
> String valueOfSomething;
>
> //getter and setters that are public
> }
>
> In a singlton class I have the following:
>
> Public Map<String, LineAmounts> MyLineAmounts = new HashMap<String,
> LineAmount>();
>
> And I access the new map with a public add and retreive method that evokes
> either the put or get methods of the map. I feel this is more robust.
>
> Jim
>
> -----Original Message-----
> From: program-java-bounce@xxxxxxxxxxxxx [mailto:
> program-java-bounce@xxxxxxxxxxxxx] On Behalf Of Steve Meacham
> Sent: September 3, 2010 12:42
> To: program-java@xxxxxxxxxxxxx
> Subject: [program-java] Re: Java: Redimensioning my existing array.
>
> Please allow me to offer a didactic review of what Java arrays actually
> are.  This will be a little bit long, so wait to read it until you have time
> to go step-by-step through what would be about a whole page in a textbook.
>
> // This is a single, primitive, double
> double d;  // no jokes, guys
>
> // This is a single dimensional array of primitive doubles double[] ad;
>
> // This is a single dimensional array of single dimensional arrays of
> doubles, which can be used to simulate a two dimensional array double[][]
> aad;
>
> // This is a single dimensional array of single dimensional arrays of
> single dimensional arrays of doubles, which can be used to simulate a three
> dimensional array double[][][] aaad;
>
> Java only supports single-dimensional arrays.  I stopped with three, but
> most Java implementations will allow you to go up to 255 levels deep like
> this.  I don't recommend it.  Each single dimensional array allows from zero
> to Integer.MAX_VALUE elements.
>
> Please note that it isn't until you reserve the memory that the lengths are
> specified.  This allows a lot of flexibility, such as not knowing how bit to
> make the arrays until run-time.  Now, let's reserve memory for the
> two-dimensional array in the most primitive way.
>
> aad = new double[5][]; // This creates an array of five arrays of doubles
> aad[0] = new double[10]; // The creates the first one, an array of ten
> doubles
> aad[1] = new double[2]; // The creates the second one, an array of two
> doubles
> aad[2] = new double[6]; // The creates the third one, an array of six
> doubles
> aad[3] = new double[0]; // The creates the fourth one, an array of zero
> doubles
> aad[4] = new double[5]; // The creates the fifth one, an array of five
> doubles
>
> Please also note that each of these sizes could have been done with a
> variable and not known until run-time.  Try to do THAT in FORTRAN!  Of
> course, Java offers what I call "syntactic sugar" for when all the
> dimensions are the same:
>
> // This creates an array of five arrays of doubles.  It also creates five
> arrays of ten doubles each.
> aad = new double[5][10];
>
> This is good and bad at the same time.  It is good because it is flexible
> and powerful.  Bad, because not only is it confusing to just about everybody
> (no, you're not alone), but because it slows things down a bit.  In most
> languages finding the value stored in aad[2][5] is as simple and fast as
> adding two times five time the size of a double to the starting address of
> the multi-dimensional array.  In most languages, most or all of this can be
> done at compile time, making it into a simple memory de-reference.  In Java,
> however, the nested arrays must be traversed at runtime, one at a time.
>  Finding add[2][5] become "retrieve and de-reference the value at add[2];
> then find the value at add[5]."  Arrays of Objects, rather than primitives
> makes this even worse.
>
> Because of this, arrays are very unique and special-purposed in Java.  It's
> not like in Fortran where, if you can't do it in with array, it isn't worth
> doing.  I'm not sure what problem you're trying to solve, Jim, or what
> domain you're trying to represent, but in Java, using nested-arrays is
> rarely the best solution.  The main places I find them to be appropriate is
> in graphics, cryptography, and other very specialized applications.  In
> business application programming, not so much.  There, the Collection
> Classes are the main containers for multiple instances of related same-type
> data, and Classes are the main containers for related but different-type
> data.
>
> Steve
>
>
> On Fri, Sep 3, 2010 at 10:26 AM, Willem <dwillemv@xxxxxxxxx> wrote:
>
>
>        Arrays are by design not resizable. You need to copy the data to a
> bigger array.
>
>        This is what ArrayList does behind the seens, and linkedList does
> the same for adding nodes.
>        On 9/3/2010 4:24 PM, Homme, James wrote:
>
>                Hi Guru,
>
>                Maybe you can adapt the code about dynamic arrays on this
> page. It says Java can't really do dynamic arrays, but talks about a way to
> get around the problem. http://math.hws.edu/javanotes/c7/s3.html
>
>
>
>                Jim
>
>
>
>                Jim Homme,
>
>                Usability Services,
>
>                Phone: 412-544-1810. Skype: jim.homme
>
>                 Internal 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
> >
>
>
>
>                From: program-java-bounce@xxxxxxxxxxxxx [mailto:
> program-java-bounce@xxxxxxxxxxxxx] On Behalf Of Corbett, James
>                Sent: Friday, September 03, 2010 9:40 AM
>                To: 'program-java@xxxxxxxxxxxxx'
>                Subject: [program-java] Java: Redimensioning my existing
> array.
>
>
>
>                Hello all:
>
>
>
>                I have an array of type double....
>
>
>
>                Double[][] myDoubleArray = new double[2][13];
>
>
>
>                ...I now need to add an additional field.... Should I
> redimension the array like double[2][13][5] or should I invest in either an
> arrayList or HashMap?
>
>
>
>                Jim
>
>
>
>                James M. Corbett
>
>
>
>                Programmer / Analyst |
>
>                Canada Revenue Agency | Agence du revenue du Canada
>
>                875 Heron Rd.
>
>                Ottawa, On.
>
>                K1A0L5
>
>
>
>                James.Corbett@xxxxxxxxxxxxx
>
>                Telephone | Téléphone: (613) 941-1338
>
>                Facsimile | Télécopieur: (613) 941-2261
>
>
>
>                Government of Canada | Gouvernement du Canada
>
>
>
>
>
>
> ________________________________
>
>                This e-mail and any attachments to it are confidential and
> are intended solely for use of the individual or entity to whom they are
> addressed. If you have received this e-mail in error, please notify the
> sender immediately and then delete it. If you are not the intended
> recipient, you must not keep, use, disclose, copy or distribute this e-mail
> without the author's prior permission. The views expressed in this e-mail
> message do not necessarily represent the views of Highmark Inc., its
> subsidiaries, or affiliates.
>
>
>
>
>
>
>


-- 

Steve Meacham
+1 (202) 
455-8732<https://clients4.google.com/voice/embed/webCallButton?id=230865b4d19270e76c79c4ec6344ae302ccf1b69>
*routes all calls and text messages to me*

Other related posts:

  1. Home
  2. program-java
  3. Archive
  4. 09-2010