Can you explain the principle of operation of the ArrayList data structure?

ArrayList is a dynamic array in Java that automatically expands when elements are added. It uses a regular array internally, which increases in size when the current array is filled.

Main points:

• Elements are stored in an array.
• When a new element is added and the array is full, a new array of larger size (usually 50% larger or twice as large) is created, and old elements are copied into it.
• Access to elements by index occurs in constant time O(1).
• Adding an element at the end is usually O(1), but during array expansion, it is O(n).

Example usage:

ArrayList<String> list = new ArrayList<>();
list.add("Hello");
String first = list.get(0);