What is the difference between HashMap and Hashtable?
☕Coffee Chat Question
Concept Made Simple
“What is the difference between HashMap and Hashtable?”
🧠Mind Map Answer
Remember It Faster
Same idea — key/value storage — but built for different eras.
Rule of thumb: use HashMap by default. If you need concurrency, reach for ConcurrentHashMap — Hashtable is legacy.
⌨️Hands-on Keyboard
Learn by Doing
Map<String, String> map = new HashMap<>();
map.put(null, "ok"); // allowed
Map<String, String> table = new Hashtable<>();
// table.put(null, "x"); // throws NullPointerException🔥What If?
Think Beyond the Expected
Why is Hashtable considered slow?
Every method is synchronized, so only one thread touches the table at a time. ConcurrentHashMap locks only a segment/bucket, allowing concurrent reads and writes.
Continue Learning with AI
Take this question deeper with your favourite AI assistant. Pick a depth, copy the prompt, or open it directly — AI is your learning companion, not a shortcut.
Plain-language foundations
I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner. Topic: Collections (Core Java) Interview question: "What is the difference between HashMap and Hashtable?" Please: 1. Explain the core idea in simple, plain language, using an everyday analogy. 2. Define any technical terms you use. 3. Walk through one small, concrete example. 4. Finish with a single sentence I can easily remember. Keep the tone friendly and assume I'm new to this topic.
Was this answer helpful?
⭐ Featured Products
Support our platform by exploring our recommended products.
As an Amazon affiliate, purchases through these links may earn us a small commission — at no extra cost to you. It helps keep Full Stack Interview Guru free.