Java ArrayList copy

java arraylist
user309281 picture user309281 · Jun 30, 2011 · Viewed 364.5k times · Source

I have an ArrayList l1 of size 10. I assign l1 to new list reference type l2. Will l1 and l2 point to same ArrayList object? Or is a copy of the ArrayList object assigned to l2?

When using the l2 reference, if I update the list object, it reflects the changes in the l1 reference type also.

For example: 

List<Integer> l1 = new ArrayList<Integer>();
for (int i = 1; i <= 10; i++) {
    l1.add(i);
}

List l2 = l1;
l2.clear();

Is there no other way to assign a copy of a list object to a new reference variable, apart from creating 2 list objects, and doing copy on collections from old to new?

Answer

Jon Skeet picture Jon Skeet · Jun 30, 2011

Yes, assignment will just copy the value of l1 (which is a reference) to l2. They will both refer to the same object.

Creating a shallow copy is pretty easy though:

List<Integer> newList = new ArrayList<>(oldList);

(Just as one example.)

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