The mystery of the vanishing variables...

Question

Hello,
I've got a bit of a problem re data that vanishes from some of my Vectors.
One class - Transfers - in its update() method, sends data in 2 Vectors to classes Tracking, and Reserve, in that order.
public class Transfers
  update()
   new Tracking(vec1, vec2);
   new Reserve( vec1, vec2);
}Class Tracking's constructor receives the 2 Vectors sent to it so:
  public Tracking(Vector vec1, Vector vec2)
   this.vec1 = vec1;
   this.vec2 = vec2;
  }Once all processing has been done in Tracking, I remove all data elements from the vectors passed to it.
Program flow then passes to the Reserve class, which receives the same 2 Vectors that were passed to the Tracking class.
But, at this stage, there is no data in vec1 or vec2 to pass to the Reserve class.
It seems to me that when the data in Tracking.vec1 and Tracking.vec2 was deleted, the same happened to the data in Transfers.vec1, and Transfers.vec2. But why? Surely, it's only a copy of the data in the Transfers Vectors that is being passed to Tracking and Reserve?
What can I do to prevent the data in the Vectors from vanishing?
Thanks,
Hasman.

Answer 1

The next can be an example. ArrayList is used instead of Vecter.
// import java.util.*;
public class H {
public static void main(String[] args) throws java.lang.Exception{
ArrayList list = new ArrayList();
list.add(new A(0));
list.add(new A(1));
list.add(new A(2));
/*ArrayList scopy = new ArrayList(list);// data is changed in this case if those in the original "list" are changed
((A)list.get(1)).change(100);
for(int j=0;j<scopy.size();j++){
   System.out.println(((A)scopy.get(j)).n);
ArrayList dcopy = new ArrayList(); // in this case data is not changed
for(int j=0;j<list.size();j++){
   Object a = ((A)(list.get(j))).clone();
   dcopy.add(a);
((A)list.get(2)).change(1000);
for(int j=0;j<dcopy.size();j++){
   System.out.println(((A)dcopy.get(j)).n);
}// end of class H
class A implements Cloneable{  // instances of this class will be stored in ArrayList
public int n;
  A(int i){
     this.n = i;
  public void change(int m){
     this.n = m;
  public Object clone(){
     return new A(this.n);
}