Data Structures

Array

A fixed-size, indexed collection of elements of the same type. Best for storing a fixed number of elements with fast access by index.

int[] arr = new int[5];  // Array of 5 integers, default value is 0

ArrayList

A dynamically resizing array that allows random access and provides flexible resizing. Ideal for collections with frequent access and occasional insertions or deletions.

ArrayList<Integer> arrayList = new ArrayList<>();  // Empty ArrayList of integers

LinkedList

A linear collection where each element (node) contains a reference to the next element. In a double-linked list, each element also holds a reference to the previous element. Best when frequent insertions and deletions at the beginning or end are required.

List<String> linkedList = new LinkedList<>();  // Empty LinkedList of strings

Hashmap

A collection of key-value pairs, where keys are unique, and each key maps to a value. It uses a hash table for fast lookups. Ideal for fast lookups, updates, and retrieval by unique keys.

Map<String, Integer> map = new HashMap<>();  // Empty HashMap with String keys and Integer values

HashSet

A collection that stores unique elements, backed by a hash table. - essentially a HashMap without a value, just the key. Ideal for storing unique elements where fast lookup, insertion, and deletion are needed.

HashSet<String> hashSet = new HashSet<>();  // Empty HashSet of strings

TreeMap

A sorted map implementation based on a red-black tree, where keys are ordered. Best when elements need to be stored in a specific order or need to be traversed in sorted order.

Map<String, Integer> treeMap = new TreeMap<>();  // Empty TreeMap with String keys and Integer values (sorted by keys)

TreeSet

A collection that implements the Set interface, backed by a TreeMap (often a red-black tree). It stores unique elements in a sorted order. Best when you need to store unique elements that should be kept sorted and require fast access, insertion, and removal with ordering. It’s ideal when you need a sorted set.

Set<Integer> treeSet = new TreeSet<>();  // Empty TreeSet of integers (sorted by natural order)

Comparing different data structures and their operations