Strange(?) behaviour

[Stephen Pride]

I wrote a small program that reads in integer values from a comma-dilimited file. What's strange is that depending where I place a local integer array, the output changes. Here is the code ...

import java.io.*;
import java.util.*;
class Entry
{
   int[] d = new int[5];
   public Entry(int[] d) { this.d = d; }
   public int[] getData() { return this.d; }
}
public class ReadData
{
   Vector mem = new Vector();
   
   public static void main(String[] arg)
   {
      new ReadData();
   }
   
   public ReadData()
   {
      // read data from a comma-dilimited file
      // lines are in format: n1,n2,n3,n4,n5
  
      FileReader fr = null;
      try {
         fr = new FileReader("xyz.txt");
         BufferedReader br = new BufferedReader(fr);
         String s = null;
//       int[] d = { 0,0,0,0,0 };   // BAD
         while ((s = br.readLine()) != null)
         {
            StringTokenizer st = new StringTokenizer(s,",");
            int col = 0;
            int[] d = { 0,0,0,0,0 };  // GOOD
            while (st.hasMoreTokens())
            {
               String t = st.nextToken();
               d[col] = Integer.parseInt(t);
               col++;
            }
            mem.add(0, new Entry(d));
         }
      } catch(Exception e) {
         e.printStackTrace();
      } finally {
         if ( fr != null)
            try { fr.close(); } catch(Exception ee) { }
      }
   }
}

Now, if I uncomment the line that says "// BAD" and comment the line that says "// GOOD", the data stored in the Vector is always the same for each element.
IOW, if the first line read is "1,2,3,4,5" and the second line read is "6,7,8,9,0", executing the original code will produce a Vector with two Element objects: the first (0-index) Element object will have the integer data {1,2,3,4,5} and the second (1-index) Element object will have the integer data {6,7,8,9,0}. However, if I change the code as described in the previous paragraph, the first Element object will have the integer data {6,7,8,9,0} and the second Element object will have the integer data {6,7,8,9,0}.
Anyone know why?

[Ilja Preuss]

Because in the second case, both Entry objects are referring to the same array object.

[Greg Charles]

Yes, Ilja is right. What you probably want to do during the Entry constructor, since you've already created an array in Entry, is just copy the values from the parameter "d". Actually, it's probably better to wait and create the array in the constructor, since you don't know the passed array will always have size 5. Take a look at System.arraycopy() in the Java Docs.