Hello all,I've tried many different ways to assign a value to the position of mychoice in a data structure, ArrayList and would appreciate any hintshow to do this.  My program as follows (short version):import java.util.*;    public class MyProg1 {       public static void main(String[] args) {          ArrayList data = new ArrayList();          ArrayList [] table = new ArrayList[5];          data.add(1);          data.add(3);          data.add(4);           for ( int i = 0; i < 3; i++ ){              //table.add(data.get(i));      //these are 3 differentfailed ways that I've tried              //table[i]=data.get(i);             //table(i)=data.get(i);             table[0] = data;         } }Essentially, I want to assign the first value of data to the firstelement of table, the second value of data to table(2,0), and 3rdelement to table(3,0).  The statement table[0] = data puts the wholearrayList data to table(0) which is not what I want.  How do youreference the elements of table?  I thought I understood thereferening until now.  :xAny help is appreciated.-t

On Nov 10, 5:50 pm, Taria <mche...@hotmail.com> wrote:> Hello all,>> I've tried many different ways to assign a value to the position of my> choice in a data structure, ArrayList and would appreciate any hints> how to do this.  My program as follows (short version):>> import java.util.*;>     public class MyProg1 {>        public static void main(String[] args) {>           ArrayList data = new ArrayList();You are using an "unchecked" ArrayList here, try:  "ArrayList<Integer> data = new ArrayList<Integer>();">           ArrayList [] table = new ArrayList[5];>           data.add(1);>           data.add(3);>           data.add(4);>            for ( int i = 0; i < 3; i++ ){>               //table.add(data.get(i));      //these are 3 different> failed ways that I've tried>               //table[i]=data.get(i);>              //table(i)=data.get(i);Wrong syntax, and trying to assign to empty elements.>              table[0] = data;>          }>  }>> Essentially, I want to assign the first value of data to the first> element of table, the second value of data to table(2,0), and 3rd> element to table(3,0).  The statement table[0] = data puts the whole> arrayList data to table(0) which is not what I want.  How do you> reference the elements of table?  I thought I understood the> referening until now.  :x>> Any help is appreciated.You are going to get a lot of warnings using "unchecked"arrays, but you can reduce that a little bit as follows:public class MyProg1 {  public static void main( String[] args )   {    ArrayList<Integer> data = new ArrayList<Integer>();    ArrayList table[] = new ArrayList[ 5 ];    Arrays.fill( table, new ArrayList<Integer>() );    data.add( 1 );    data.add( 3 );    data.add( 4 );    for( int i = 0; i < data.size(); i++ ) {      table[ i ].add( i, data.get( i ) );     }   } }To suppress the warnings completely, you will (AFAIK),need to use an annotation, or use the '-nowarn' flagat the command line.--Chris

Taria wrote:>> I've tried many different ways to assign a value to the position of my>> choice in a data structure, ArrayList and would appreciate any hints>> how to do this.  My program as follows (short version):>>>> import java.util.*;>>     public class MyProg1 {Excellent name for the class.  Seriously - many newbies would use a name part like "Class" for something that we already know is a class.  You gave a correctly-capitalized name that has a meaning - it's your program number one, hence "MyProg1".  Perfect.>>        public static void main(String[] args) {>>           ArrayList data = new ArrayList();Chris ( Val) pointed out:> You are using an "unchecked" ArrayList here, try:>   "ArrayList<Integer> data = new ArrayList<Integer>();"Taria wrote:>>           ArrayList [] table = new ArrayList[5];You do not need an array of ArrayList.  Your 'table' is not an ArrayList, but a group of five ArrayLists.>>           data.add(1);>>           data.add(3);>>           data.add(4);>>            for ( int i = 0; i < 3; i++ ){>>               //table.add(data.get(i));      //these are 3 differentThis failed because data.get(i) is an Integer (not an int), and table needs a whole ArrayList, not just one Integer.Also because add() is not a method of an array.>> failed ways that I've tried>>               //table[i]=data.get(i);This failed because data.get(i) is an Integer (not an int), and table needs a whole ArrayList, not just one Integer.>>              //table(i)=data.get(i);You use bracket notation '[]' not parentheses '()' to assign to an array element.This failed because data.get(i) is an Integer (not an int), and table needs a whole ArrayList, not just one Integer.>>              table[0] = data;>>          }>>  }>>>> Essentially, I want to assign the first value of data to the first>> element of table, the second value of data to table(2,0), and 3rd>> element to table(3,0).  The statement table[0] = data puts the whole>> arrayList data to table(0) which is not what I want. You cannot do what you want because table is an array of ArrayList, not an array of Integer.>> How do you reference the elements of table?  I thought I understood the>> referening until now.  :xtable[0] = data;just like you did.  Each element of table is a whole entire ArrayList (possibly empty or null).Oh, you want table to hold Integers instead of ArrayLists?  Then you want:List <Integer> data = new ArrayList <Integer> ();data.add(1);data.add(2);data.add(3);Integer [] table = new Integer [5];for ( int ix = 0; ix < Math.min( data.size(), table.length ); ++ix){   table [ix] = data.get( ix );}FWIW, arrays and collections make uneasy bedfellows.-- Lew

Chris ( Val ) wrote:> public class MyProg1>  {>   public static void main( String[] args )>    {>     ArrayList<Integer> data = new ArrayList<Integer>();>     ArrayList table[] = new ArrayList[ 5 ];> >     Arrays.fill( table, new ArrayList<Integer>() );> >     data.add( 1 );>     data.add( 3 );>     data.add( 4 );> >     for( int i = 0; i < data.size(); i++ ) {>       table[ i ].add( i, data.get( i ) );>      }>    }>  }> Whoops, Chris, you're wrong :-(Specifically>     Arrays.fill( table, new ArrayList<Integer>() );This will put the *same* ArrayList into every slot in table.While I think the OP is going about this problem the wrong way, the solution he needed was:table[i].add(data.get(i));To the OP:Try not to mix arrays and Collections.  As a matter of fact, for the most part its best to deal with Collections, and avoid arrays all together.-- Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>

Hello all,Ohhh, thank you so much for addressing those 'unchecked' warnings.  Ithink I'm up to 15 of them now and have been ignoring them.  :)Thank you guys for excellent advice!  I think I spent almost fourhours on that small segment, trying to assign values where I wantedthem to go (instead of them 'magically' appearing somewhereelse.  :p)  I learned a lot of things by experimenting though.Arrays and collections don't make a good mix eh?  Ok, so I reorganizedmy code to exclude the array within an ArrayList.  I thought I neededto do that to create the matrix structure I ultimately wanted.  So nowI have an ArrayList of ArrayLists where table's definition not anarray.  In short, I've done this (code doesn't include the fix toremove the unchecked warnings):....   ArrayList table = new ArrayList();   {ArrayList data = new ArrayList();   data.add(1);   data.add(3);   data.add(2);   table.add(data);   }   {ArrayList data = new ArrayList();   data.add(11);   data.add(13);   data.add(12);   table.add(data);   } ....This is what worked for me, I assigned a list of data items to eachrow of table.  And I have a question about those curly braces.  Idiscovered them last night and it appears they make whatever code inthe middle of them, local within the brackets.  I don't remember everseeing them used in examples of other ppl's code anywhere before.  ButI've found that without them, table assumes the values of only thelast set of assignments instead of 2 unique sets of assignment.  Maybeit's better to make those parts into methods?  Just curious about theusage of those.Thank you again for your help.-t

Taria wrote:> Hello all,> > Ohhh, thank you so much for addressing those 'unchecked' warnings.  I> think I'm up to 15 of them now and have been ignoring them.  :)> > Thank you guys for excellent advice!  I think I spent almost four> hours on that small segment, trying to assign values where I wanted> them to go (instead of them 'magically' appearing somewhere> else.  :p)  I learned a lot of things by experimenting though.> > Arrays and collections don't make a good mix eh?  Ok, so I reorganized> my code to exclude the array within an ArrayList.  I thought I needed> to do that to create the matrix structure I ultimately wanted.  So now> I have an ArrayList of ArrayLists where table's definition not an> array.  In short, I've done this (code doesn't include the fix to> remove the unchecked warnings):> > ....>    ArrayList table = new ArrayList();>    {ArrayList data = new ArrayList();>    data.add(1);>    data.add(3);>    data.add(2);>    table.add(data);>    }>    {ArrayList data = new ArrayList();>    data.add(11);>    data.add(13);>    data.add(12);>    table.add(data);>    }>  ....> > This is what worked for me, I assigned a list of data items to each> row of table.  And I have a question about those curly braces.  I> discovered them last night and it appears they make whatever code in> the middle of them, local within the brackets.  I don't remember ever> seeing them used in examples of other ppl's code anywhere before.  But> I've found that without them, table assumes the values of only the> last set of assignments instead of 2 unique sets of assignment.  Maybe> it's better to make those parts into methods?  Just curious about the> usage of those.Good questions.The curly braces introduce a "block" of code with "local scope".  Within each block you *redeclared* the variable 'data'.  Without the inner sets of curly braces, the scope of the first declaration would have overlapped the second, causing a conflict.However, if you simply *re-use* the variable that problem goes away:public class Matriculate{   List< List <Integer> > table     = new ArrayList< ArrayList <Integer> > ();  public Matriculate()  {    // the table will now contain zero rows    assert table.size() == 0;    // here row is declared the one and only time    // and initialized for the first of more than one time    List <Integer> row = new ArrayList <Integer> ();    row.add( 1 );    row.add( 2 );    row.add( 3 );    row.add( 5 );    table.add( row );    // the table will now contain one row    assert table.size() == 1;    row = new ArrayList <Integer> ();    // notice - re-used, not re-declared    // the variable 'row' now points to a whole    // new ArrayList    row.add( 1 );    row.add( 2 );    row.add( 4 );    row.add( 8 );    row.add( 16 );    table.add( row );    // the table will now contain two rows    assert table.size() == 2;  }  // now the variable 'row' is out of scope  // the closing curly brace killed it  public List< List <Integer>> getTable()  {    return Collections.unmodifiableList( table );  }}-- Lew

On Fri, 09 Nov 2007 22:50:38 -0800, Taria <mchew02@hotmail.com> wrote,
quoted or indirectly quoted someone who said :

>I've tried many different ways to assign a value to the position of my
>choice in a data structure, ArrayList and would appreciate any hints
>how to do this.  My program as follows (short version):

Are you confusing arrays and ArrayLists.

See http://mindprod.com/jgloss/array.html
http://mindprod.com/jgloss/arraylist.html

reviewing the basics of each should get help you solve this and many
similar problems.
-- 
Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com

On Nov 11, 5:47 am, Daniel Pitts<newsgroup.spamfil...@virtualinfinity.net> wrote:> Chris ( Val ) wrote:>>>> > public class MyProg1> >  {> >   public static void main( String[] args )> >    {> >     ArrayList<Integer> data = new ArrayList<Integer>();> >     ArrayList table[] = new ArrayList[ 5 ];>> >     Arrays.fill( table, new ArrayList<Integer>() );>> >     data.add( 1 );> >     data.add( 3 );> >     data.add( 4 );>> >     for( int i = 0; i < data.size(); i++ ) {> >       table[ i ].add( i, data.get( i ) );> >      }> >    }> >  }>> Whoops, Chris, you're wrong :-(> Specifically>     Arrays.fill( table, new ArrayList<Integer>() );>> This will put the *same* ArrayList into every slot in table.Wow :-)My apologies to the OP.I guess I assumed that "new ArrayList<Integer>()" wouldcreate and add a *new unique copy* of an ArrayList intoeach slot of the array.Seems I have a bit more to learn about Java references.Thank you for the correction.> While I think the OP is going about this problem the wrong way, the> solution he needed was:>> table[i].add(data.get(i));Yes, I had that originally, but whilst experimentingwith the version I posted, I forgot to revert back tothis one.> To the OP:> Try not to mix arrays and Collections.  As a matter of fact, for the> most part its best to deal with Collections, and avoid arrays all together.Good advice.--Chris

On Sat, 10 Nov 2007 12:21:58 -0800, Taria <mchew02@hotmail.com> wrote,quoted or indirectly quoted someone who said :>remove the unchecked warnings see http://mindprod.com/jgloss/generics.html for a simplified intro to how to generify your code.-- Roedy Green Canadian Mind ProductsThe Java Glossaryhttp://mindprod.com