Does Java\'s ArrayList Assignment Create a Copy or a Shared Reference?

Copying ArrayList Objects in Java

In Java, ArrayLists are dynamic arrays that can be used to store elements of a specified type. When working with ArrayLists, it's important to understand how assignment behaves.

Question: Shared Reference or Copy?

Suppose we have an ArrayList l1 with 10 elements and assign it to another variable l2. Do l1 and l2 point to the same ArrayList object, or is a copy of the object assigned to l2?

Answer: Shared Reference

Assignment in Java simply copies the value of the variable, which in this case is a reference to the ArrayList object. As a result, l1 and l2 will both refer to the same ArrayList object.

For example:

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

List l2 = l1;
l2.clear();

In this case, clearing l2 also affects l1 because they both point to the same object.

Creating a Copy

To create a copy of an ArrayList object, a shallow copy can be made by creating a new ArrayList and adding the elements from the original list to the new one:

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

This method results in a separate ArrayList object with the same elements as the original.

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