Mid-levelMid (3–6 yrs)JavaSpring BootGoogleAmazonOracle
HashMap internals
Explain HashMap internals and what changed after Java 8.
Answers use simple, clear English.
Quick interview answer
HashMap uses an array of buckets. Colliding keys form a linked list; after Java 8, long collision chains convert to balanced trees (TreeNodes) for O(log n) worst-case. Capacity, load factor (0.75), and key hashCode/equals quality dominate performance.
Detailed answer
HashMap uses an array of buckets. Colliding keys form a linked list; after Java 8, long collision chains convert to balanced trees (TreeNodes) for O(log n) worst-case. Capacity, load factor (0.75), and key hashCode/equals quality dominate performance. ConcurrentHashMap is required for concurrent writes.
midsenior#collections#jvm