Need Help with ArrayList - NullPointerException

[achana chan]

I refer to this thread
http://www.coderanch.com/t/395679/java/java/ArrayList-still-getting-null-pointer
I've modified the code about fiftieth times today and still am stuck with NullPointerException at runtime:

{ txrecord = new TXRecord();
  int var_idx = txrecord.var_counter;
  System.out.println("ConfirmationFrame: " +
                     String.valueOf(var_idx));  // WORKS up to this point
  txrecord.var_acctName = "blank account name"; 
  txrecord.var_unitCost = "blank unit cost";
  System.out.println("var_acctName: " + 
                   txrecord.rec_acctName[var_idx]); // NULLPOINTEREXCEPTION

I just cannot get pass this bit of code... What is it, for sanity's sake ?!?

import java.util.*;
import java.io.*;
/**
 *  A TXRecord object encapsulates a transaction records
 */
public class TXRecord
{ // variables set at runtime by other applets...
  public int var_counter = 0;
  public String var_acctName = "blank";
  public String var_unitCost = "blank";
  public String[] rec_acctName;
  public String[] rec_unitCost;
  //
  public void init()
  {
    //List lst_acctName = new ArrayList(var_counter+1);
    //List lst_unitCost = new ArrayList(var_counter+1);
    rec_acctName = new String[100];
    rec_acctName = new String[100];
    // add runtime values to list elements...
    rec_acctName[var_counter] = var_acctName;
    rec_unitCost[var_counter] = var_unitCost;
    //lst_acctName.add(rec_acctName[var_counter]);
    //lst_unitCost.add(rec_unitCost[var_counter]);
    var_counter += 1;
   }
}

[Arnold Reuser]

use
public TXRecord() {
....
}
instead of
public void init() {
....
}
Try reading one of the great java-books of bruce eckel. You can download it from http://64.78.49.204/ I've read it several years ago and still like it.

[achana chan]

Arrgh, looking at the wrong place, misled by the line number for the NullPointerException.
Yes it works like that.
But I don't want the applet to know anything about the indexing in TXRecord, ideally it assigns values to the variables var_<name>

{ txrecord = new TXRecord();
  int var_idx = txrecord.var_counter;
  System.out.println("ConfirmationFrame: " + String.valueOf(var_idx));
  txrecord.var_acctName = "blank account name";
  txrecord.var_unitCost = "blank unit cost";
  System.out.println("var_acctName: " + 
           txrecord.rec_acctName[var_idx]); // <---- use save index value
  System.out.println("var_unitCost: " + 
           txrecord.rec_unitCost[var_idx]); // <---- use saved index value

On the receiving end, we now have this code:

import java.util.*;
import java.io.*;
/**
 *  A TXRecord object encapsulates a transaction records
 */
public class TXRecord
{ // variables set at runtime by other applets...
  public int var_counter = 0;
  public String var_acctName = "blank";
  public String var_unitCost = "blank";
  public String[] rec_acctName;
  public String[] rec_unitCost;
  //
  public TXRecord()
  {
    //List lst_acctName = new ArrayList(var_counter+1);
    //List lst_unitCost = new ArrayList(var_counter+1);
    rec_acctName = new String[100];
    rec_unitCost = new String[100];
    // add runtime values to list elements...
    //lst_acctName.add(rec_acctName[var_counter]);
    //lst_unitCost.add(rec_unitCost[var_counter]);
    var_counter += 1;
   }
   public void init()
   {
    rec_acctName[var_counter] = var_acctName; // <----- not assigning value
    rec_unitCost[var_counter] = var_unitCost; // <----- ditto
   }
}

The console output looks like this

[achana chan]

the console output looks like this:

system datetime stamp: Feb 25, 2004 7:43:57 PM
ConfirmationFrame: 0
var_acctName: null
var_unitCost: null

[Chandra Bairi]

Whatever values you are assigning to the String arrays that is done in the init() function but that function is never called from the TxnRecord() constructor. then how can the values be assigned . you have to call the init() function at the end of the constructor and probably you will get the desired results.
Thanks
Shekar.

[achana chan]

Thanks all, for giving me your time and your assistance.
It was very much appreciated.