Interview Question

HashMap vs Hashtable?

HashMap is modern and unsynchronized; Hashtable is legacy synchronized storage.

💡 Concept ✅ Quick Revision ☕ Java

Answer

HashMap and Hashtable are hash-based maps with different legacy and synchronization behavior. • Hashtable methods are synchronized and reject null keys and values. • HashMap is unsynchronized and permits one null key and null values. • ConcurrentHashMap is usually preferred for scalable concurrent access.

Example

Code

var map = new java.util.HashMap<String, Integer>();
map.put(null, 1);
System.out.println(map.get(null));

Output

Quick Revision

HashMap is modern and unsynchronized; Hashtable is legacy synchronized storage.

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