Bug using list and treeset

Question

I have a real world problem where I get a list of retail store location and get the distance from group of starting locations and find the 10 closest location for each starting locations. I get returned from getdata a list of stores loop through each store and calculate the distance and put them in a treeset for sorting. Problem is when the second set of data is added to the treeset the original set is replace with a duplicate set of the second set. a very simple test case for this is follows:
package treeset;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.TreeSet;
import java.io.Serializable;
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
// Class TreeSetExample
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
* The TreeSetExample demonstreates a odity in the sorting of list using a treeset
* @version 1.0, 04/06/2011
* @author  Douglas Nelson
* @author  copyright Oracle 2011
* @author  Unauthorized use, duplication or modification is strictly prohibited.
public class TreeSetExample extends Object {
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// start constructor
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
* Constructs a TreeSetExample object
public TreeSetExample() {
} // end constructor
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// start getData
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
* getDatea
public List<SimpleVO> getData() {
   List<SimpleVO> returnList = new LinkedList<SimpleVO>();
   SimpleVO simpleVO = null;
   for (int i = 0;i < 5;i++) {
      returnList.add(new SimpleVO());
   } // end for
   return(returnList);
} // end getData
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// start runTest
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
* runTest - Test the insert sorting of a tree set with a list of data
* @param loopCount number of time to load data into the saveset
public void runTest(int loopCount) {
   List<SimpleVO>    simpleList   = getData();
   SimpleVO          simpleVO     = null;
   TreeSet<SimpleVO> saveSet      = new TreeSet<SimpleVO>(new simpleComparator());
   SimpleVO          tempSimpleVO = null;
   Iterator<SimpleVO> iterator      = null;
   Iterator<SimpleVO> printIterator = null;
   int id = 0;
   for (int i = 0; i < loopCount;i++) {
      iterator = simpleList.iterator();
   // for each of the user's zip codes find the distance to the RSL
   while (iterator.hasNext()) {
      simpleVO = iterator.next();
      id ++;
      simpleVO.setName("" + id);
      saveSet.add(simpleVO);
   } // end while
   // print saveset at the end of each load
   System.out.println("list count after loop [" + (i + 1) + "] number of elements = [" + saveSet.size() + "] contents:");
   printIterator = saveSet.iterator();
   while(printIterator.hasNext()) {
      tempSimpleVO = printIterator.next();
      System.out.println(" save simpleVO name = [" + tempSimpleVO.getName() + "]");
   } // end while
   } // end For
} // end runTest
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// start main
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
* IbotMailParser main thread
* @param arg standard main input string array.
public static void main(String[] arg) {
   System.out.println("Main - Started");
   try {
      System.out.println("*************** starting test 1 *********************");
      TreeSetExample treeSetExample = new TreeSetExample();
      treeSetExample.runTest(1);
      System.out.println("\n");
      System.out.println("\n");
      System.out.println("*************** starting test 2 *********************");
      treeSetExample.runTest(2);
   } // end try
   catch (Exception any) {
      System.out.println("Exception [" + any.getMessage() + "]");
   } // end catch
   System.out.println("Main - we gone bye-bye...!");
} // end main
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
// Class SimpleVO
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
* The SimpleVO is a value object pattern used for this example
* @version 1.0, 04/06/2011
* @author  Douglas Nelson
* @author  copyright Oracle 2011
* @author  Unauthorized use, duplication or modification is strictly prohibited.
public class SimpleVO extends Object {
    * Default user name for Oracle connection.
   private String name = "";
   //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   // start getName
   //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
    * Returns the name value associated with this attribute
    * @return String - the Name parameter
   public String getName() {
      return(name);
   } // end getName
   //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   // start setName
   //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
    * Sets the name value for this attribute
    * @param newName the Name to be set
   public void setName(String newName) {
      if (newName != null) {
         name = newName.trim();
      } // end if
   } // end setName
} // end SimpleVO
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
// Class simpleComparator
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
* The SimpleComparator is a comparator object used for sorting simple value objects
* @version 1.0, 04/06/2011
* @author  Douglas Nelson
* @author  copyright Oracle 2011
* @author  Unauthorized use, duplication or modification is strictly prohibited.
public class simpleComparator implements Comparator<SimpleVO>, Serializable {
   //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   // start getName
   //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
    * Returns the name value associated with this attribute
    * @return String - the Name parameter
   public int compare(SimpleVO simpleVO_1, SimpleVO simpleVO_2) {
      return(1);
   } // end compare
} // end SimpleComparator
} // end class TreeSetExample
output :
c:\treeset>java treeset.TreeSetExample
Main - Started
*************** starting test 1 *********************
list count after loop [1] number of elements = [5] contents:
save simpleVO name = [1]
save simpleVO name = [2]
save simpleVO name = [3]
save simpleVO name = [4]
save simpleVO name = [5]
*************** starting test 2 *********************
list count after loop [1] number of elements = [5] contents:
save simpleVO name = [1]
save simpleVO name = [2]
save simpleVO name = [3]
save simpleVO name = [4]
save simpleVO name = [5]
list count after loop [2] number of elements = [10] contents:
save simpleVO name = [6]
save simpleVO name = [7]
save simpleVO name = [8]
save simpleVO name = [9]
save simpleVO name = [10]
save simpleVO name = [6]
save simpleVO name = [7]
save simpleVO name = [8]
save simpleVO name = [9]
save simpleVO name = [10]
Main - we gone bye-bye...!
Edited by: EJP on 7/04/2011 10:44: added code tags. Please use them.

Answer 1

user12607386 wrote:
I have a real world problem where I get a list of retail store location and get the distance from group of starting locations and find the 10 closest location for each starting locations. I get returned from getdata a list of stores loop through each store and calculate the distance and put them in a treeset for sorting. Problem is when the second set of data is added to the treeset the original set is replace with a duplicate set of the second set. a very simple test case for this is follows:Well, first off, when you post code, please put it in '' tags; but the basic problem is your[code]simpleVO.setName("" + id);[/code]line. A name should normally be *final*, so you shouldn't be able to set it at all.
When you add the second set of 5 to your Set, you're simply changing the name of the first 5 you just added, but since your Comparator doesn't actually do anything useful, it allows the second 5 to be added, which, of course, then show up as duplicates.
My advice: +THINK+ about what you want to do; don't just sit down and code. If need be, get out a pencil and paper and write out in English the steps you need.
Winston