#2 most askedVery commonMediumCollections

How does HashMap work internally?

New to Collections? Learn it from scratch first
Hash Maps & Sets →

🏢 Asked in real interviews

No reports yet. Were you asked this? Be the first to say where.

I was asked this

Walk through what happens inside a HashMap on put and get. What are collisions, and what changed in Java 8?

🧭 map.put("cat", 3), then map.get("cat")

Key "cat"

hashCode + spread

Bucket 5

Chain / tree

Press Next to follow a request through the system.

🎤 Answer it out loud, then check yourself

Say your answer as if the interviewer is listening (30–90 seconds). Then reveal what a strong answer covers and tick what you said.

☕ Java example · compiled and run to verify it works

Map<String, Integer> ages = new HashMap<>();
ages.put("cat", 3);
ages.put("dog", 5);
ages.put("cat", 4);           // same key: the value is replaced
System.out.println(ages.get("cat") + " " + ages.size());
System.out.println(ages.getOrDefault("cow", 0));

Answer out loud first, then compare.

Want to rehearse it?
Answer this to the AI interviewer and get a verdict →