What is an ArrayList?

ArrayList is a dynamic array in Java, which is part of the Collection Framework. It implements the List interface.

Main characteristics:

• Resizable: The size of the ArrayList can dynamically increase or decrease as elements are added or removed.
• Index access: Elements are stored in insertion order and accessible by an integer index starting from 0.
• Allows null: It can contain null elements.
• Allows duplicates: It can contain repeated elements.
• Not synchronized: Not thread-safe by default. For a thread-safe version, you can use Collections.synchronizedList(new ArrayList<...>()).
• Search: Efficient for operations that access elements by index (O(1)).
• Insert/Delete: Insertion and deletion operations can be slow (O(n)), especially at the beginning or middle of the list, as it may require shifting subsequent elements.

Example of creation:

// Example of creating an ArrayList of strings
ArrayList<String> names = new ArrayList<>();

Main methods:

Method	Description
add(E e)	Adds an element to the end of the list
add(int index, E element)	Inserts an element at the specified index
get(int index)	Returns the element at the specified index
remove(int index)	Removes the element at the specified index
size()	Returns the number of elements
isEmpty()	Checks if the list is empty
contains(Object o)	Checks if the list contains the specified element
clear()	Removes all elements