Collections Framework

The Java Collections Framework defines the standard data-structure interfaces and implementations every Java program depends on. Choosing the right collection — ArrayList vs. LinkedList, HashMap vs. TreeMap — and understanding the contracts of equals, hashCode, and ordering is essential for writing correct, performant code.

What You'll Find Here

Notes are being added. Planned topics:

Topic	Description
Collections Hierarchy	Iterable → Collection → List/Set/Queue; why Map is separate.
List	ArrayList (O(1) get) vs. LinkedList (O(1) add/remove at ends).
Set	HashSet, LinkedHashSet, TreeSet — duplicates, ordering, performance.
Map	HashMap, LinkedHashMap, TreeMap, ConcurrentHashMap — choosing the right map.
Queue & Deque	ArrayDeque, PriorityQueue, BlockingQueue for task patterns.
Iterators & for-each	Iterator protocol, ConcurrentModificationException, enhanced-for loop.
Sorting & Ordering	Comparable (natural order on the class) vs. Comparator (external order).
Immutable Collections	List.of, Set.of, Map.of (Java 9+); Collections.unmodifiableList.

Learning Path

1. Collections Hierarchy — understand the interface tree before picking an implementation.
2. List — ArrayList is the default; understand O-complexity trade-offs vs. LinkedList.
3. Map — HashMap internals (buckets, load factor, Java 8 tree bins) are a classic interview deep-dive.
4. Set — relies on correct equals/hashCode; review Core APIs first.
5. Sorting & Ordering — Comparable vs. Comparator appears in almost every Java interview.
6. Immutable Collections — factory methods from Java 9+ are the modern best practice.

Related Domains

• Core APIs — Object.equals/hashCode governs HashMap and HashSet.
• Java Type System — generics define List<T>, Map<K,V>, and wildcards.
• Multithreading & Concurrency — ConcurrentHashMap, BlockingQueue, and thread-safe wrappers.