What is an ArrayList?

ArrayList is a dynamic array in Java, implemented based on a regular array.

Main characteristics:

• Dynamic size: Can grow or shrink as elements are added or removed.
• Indexed access: Elements are accessible by their index (starting from 0).
• Order of elements: Maintains the order of insertion.
• Not thread-safe: Not synchronized; for multi-threaded scenarios, Vector or Collections.synchronizedList are used.
• Performance:
  • Adding/removing at the end O(1) on average (amortized time).
  • Adding/removing in the middle O(n) (requires shifting elements).
  • Access by index O(1).
  • Element search O(n).

Example usage:

import java.util.ArrayList;

// Creating an ArrayList
ArrayList<String> names = new ArrayList<>();

// Adding elements
names.add("Alice");
names.add("Bob");
names.add("Charlie");

// Accessing an element by index
String firstElement = names.get(0); // "Alice"

// Size of ArrayList
int size = names.size(); // 3

// Removing an element
names.remove("Bob"); // Removes the first found "Bob"
names.remove(0); // Removes the element at index 0 (now "Charlie")

// Iterating over elements
for (String name : names) {
    System.out.println(name);
}