How to backup ArrayList in Java?

Question

I have some data stored as ArrayList. And when I want to backup this data,java bounds two objects forever. Which means when I change values in data ArrayL

Answer 1

All of these processes make shallow copies. If you're changing properties of objects with in the array, the two arrays have references to the same instance.

List org = new java.util.ArrayList();
org.add(instance)
org.get(0).setValue("org val");
List copy = new java.util.ArrayList(org);
org.get(0).setValue("new val");

copy.get(0).getValue() will return "new val" as well because org.get(0) and copy.get(0) return the exact same instance. You have to perform a deep copy like so:

List copy = new java.util.ArrayList();
for(Instance obj : org) {
    copy.add(new Instance(obj)); // call to copy constructor
}