Question

I have used linked lists before with Strings, doubles, etc., and they always worked exactly as expected. But now I am forming a linked list of items, and whenever I add a new element to the list, all objects in the list apparently become equal to the last object.

The essential code is as below:

import java.util.*;

public class Global
{

  static public LinkedList<StockInfo> DiaryStocks = new LinkedList<StockInfo>();

  static public class StockInfo    //info related to each stock in diary
  {
    String recordDate;             
    String ticker;
    int   status;                  
    String buyDate;
    String sellDate;
    double buyPrice;
    double sellPrice;
    double nmbrShares;
  }//StockInfo

//The following function places the Diary data for a stock in the arraylist

 static public void AddDiaryData(StockInfo thisdata)
  {
    String tckr;
    int i;

    DiaryStocks.add(thisdata);

    for (i = 0; i < DiaryStocks.size(); i++)   //this is debug code
    {
      tckr = DiaryStocks.get(i).ticker;
    }
  } 
}

As I said, when single stepping through the debug code near the bottom, each time I add a new item to the list, the list size grows as it should, but the tckr item only corresponds to the last item added.

Any insights into this puzzle would be greatly appreciated.

John Doner

Answer 1

From the symptoms you are describing, it seems as if you are always adding a reference to the same StockInfo object instance to your list, rather than a reference to a new copy each time.

When that object is updated with the contents of the new entry, all list entries appear to change to reflect that latest entry.

This problem lies outside the code snippet that you posted, perhaps in the caller of the AddDiaryData method.