Using ConcurrentHashMap, how does its operation differ from a regular HashMap?

ConcurrentHashMap differs from a regular HashMap in that it is designed for safe operation in a multithreaded environment without the need for external synchronization.

Main differences:

• Thread safety: ConcurrentHashMap allows multiple threads to read and write to the map simultaneously without locking the entire structure.
• Segment-level (in older versions) or bucket-level locking: Instead of locking the entire map, ConcurrentHashMap locks only a part of the data, increasing performance.
• No locking during read operations: Reads in ConcurrentHashMap are not locked, which speeds up access.
• Iterators: Iterators of ConcurrentHashMap are weakly consistent; they reflect the state of the map at the time of their creation and may see some changes made after.

Example usage:

ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
map.put("key1", 1);
map.computeIfAbsent("key2", k -> 2);
Integer val = map.get("key1");

Unlike HashMap, which is not thread-safe and can lead to unpredictable behavior when accessed concurrently from multiple threads.