Instance of Objects

Question

I try to save an instance of an object by creating a new object with the object's values at the time. I add the new object into a vector. When the value of the object changes, why does the new object in the vector also change? How could I store the instance as it is, not changing with when the object changes?
Thanks.

Answer 1

847604 wrote:
I finally figured it out why the values have been changing. I was using a mutildimensional array and did not clone like the other things. Only a deep copy of the array would really finish the deal. When I did, no problem anymore.
Thank you guys so much.
One thing that I want to make sure about the clone() though. Since Cloneable is an interface, if I only use return super.clone(), what would it do? Do I actually have to do the following?
@Override
public Object clone() throws CloneNotSupportedException()
Obj obj1 = (Obj) super.clone();
}That's what you want, with a couple of additional bits of information.
1) If your instance variables (non-static member variables) are all primitives and immutable objects, then that's all you need. However, if any of your instance variables are mutable reference types (like List or Date), then you'll probably want to explicitly copy those as well, to get a deep copy. (Of course, if you want your clone and original to refer to the same Date object, so that they both see changes to that object, then you wouldn't do that.)
2) Not sure if "Obj" is supposed to be Object. If it is, there's never a need to cast to Object.
3) Since 1.5, Java supports covariant return types, so you can declare clone() to return an instance of your class, rather than Object.
public class Foo implements Cloneable {
  private int i; // no need for explicit deep clone of primitive
  private String s; // no need for explicit deep clone of immutable object
  private Date d; // need to explicitly deep clone mutable object
  public Foo clone() {
    Foo foo = (Foo) super.clone();
    foo.d = new Date(d); // or = d.clone(), or whatever approach is appropriate for copying a Date object
}Likewise, if your Foo has any setters that can change any of its fields, then any class that has a Foo as a member would have to explicitly deep clone its Foo, which would then (by the above) take care of cloning its own mutable members.