If I return the list in Java, is the return value a reference or an actual value?

Question

Pretty explanatory: I need to change the ArrayList that I get, but I want the original not to change.

I know this is very simple, and I'm not sure why I do not know the final answer. I think it's better late than never.

Answer 1

You will have a link to the original ArrayList .

You can create a shallow copy of the list with clone() .

See this question if you want a deep copy.

Answer 2

Everything in java will be the default link. So yes, changing the returned arraylist will change the original one.

To prevent this problem, you need to create a copy of the original. To do this, use the .clone () method.

Answer 3

If you want to change the list, but not change the original, you should not work on the list that you received in the method arguments, because you are working with a link. Better use something like this:

 public void modifyList(List myList) { myList.add("aaa"); // original *will* be modified List modifiable = new ArrayList(myList); modifiable.add("bbb"); // original will *not* be modified - only the copy } 

Answer 4

It will be the same ArrayList. If you want to get a copy, you will have to copy it yourself. Not necessarily easy if ArrayList contains complex objects!