Add list at the end of another list (not just copy references)

Question

I can't just modify the original list.

This is how I've seen it done:

List<String> l1 = new ArrayList<String>();
l1.add("Hello");
l1.add("World");
List<String> l2 = new ArrayList<String>(l1); //A new arrayList.
l2.add("Everybody");

So I now would have a new list, which is a copy of the first one. And I can modify the second without the first being changed.

And now I'm having trouble understanding how to do the same, but adding the items at the end of the list.

What I though was doing exactly the above code, and adding the list to another list. With addAll for example. But I see everywhere how this only copies references and so on, so if it's inside a method or the its a rmi code the list itself wouldn't be complete, it'd get references to the other list I just created.

Since I need to do this for many types of list not sure if going item by item is ideal. So I need to add a list at the end of another list, if that's possible at all.

Answer 1

addAll copies references of the elements of the source list to the end of the target list, it doesn't copy a reference to the source list itself.

This is not different from what the constructor you are using - new ArrayList<String>(l1) - does. If one meets your requirements, the other does too.

BTW, in the case of a List of an immutable class, such as String, it doesn't matter that the references to the elements are copied (as opposed to copies of the elements), since you can't modify the elements, so nothing you can do to the content of the second list will affect the content of the original list.