How Do References and Assignments Impact ArrayList Copies in Java?

Java Array List Copy: Understanding Reference Behavior

When working with collections in Java, it's crucial to comprehend the behavior of references and assignments. Consider an example where we have an ArrayList object l1 and assign its reference to a new variable l2.

Reference Assignment in Java

In Java, assignment operations involving objects simply copy the object's reference, not the object itself. Therefore, when l1 is assigned to l2, l1 and l2 will both point to the same ArrayList object. Any changes made through either l1 or l2 will be reflected in both references.

Example Illustration

In the provided code snippet:

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

List l2 = l1;
l2.clear();

When l1 is cleared using l2's reference, the l1 reference is also impacted. This demonstrates that both l1 and l2 point to the same ArrayList object.

Shallow Copying in Java

To create a copy of an ArrayList object (also known as a shallow copy), you can utilize the ArrayList constructor with a specific argument:

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

This approach creates a new ArrayList object with a copy of the elements from the oldList reference. Subsequent modifications to the newList will not affect the oldList reference, and vice versa.

By understanding how references work and utilizing techniques like shallow copying, you can effectively manipulate collections in Java, ensuring data integrity and avoiding unintended consequences.

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