Is using ArrayList less efficient in terms of performance when inserting elements en masse at the end of the collection?

Using ArrayList in Java for bulk insertion of elements at the end of the collection is generally efficient, but there are nuances.

ArrayList is based on an array, which automatically increases in size (resize) when capacity is reached. When adding elements to the end, if the current array is not full, the insertion occurs in amortized O(1) time.

However, when capacity is reached, elements are copied to a new, larger array, which takes O(n) time. If the insertion is very large-scale and the size is known in advance, it is recommended to:

• Initialize the ArrayList with the required initial capacity to avoid frequent resizing:

ArrayList<Integer> list = new ArrayList<>(initialCapacity);

• If capacity is not initialized, each resize involves copying, which reduces performance.

Thus, ArrayList is no less efficient for bulk insertion if the initial capacity is set correctly. Otherwise, frequent resizing can slow down the process.