HashMap Internals, Hashing Functions, Hash Collisions & TreeMap
Deep dive into HashMap internals: Node<K,V>[] bucket array, hashCode() distribution, load factor 0.75, collision resolution, and Java 8 Red-Black Tree conversion.
Inside Java 8+ HashMap Implementation
### HashMap Internal Architecture
1. **Bucket Array**: Array of `Node<K,V>` initialized to default capacity 16.
2. **Hash Computation**: `hash = (h = key.hashCode()) ^ (h >>> 16)` spreads high bits.
3. **Index Calculation**: `index = hash & (n - 1)` maps hash code into array index.
4. **Collision Handling**: Chaining via linked list nodes. When a bucket exceeds 8 nodes and array capacity >= 64, the bucket transforms into a **Red-Black Tree** ($O(\log N)$ lookup)!
