When and why should you use ConcurrentHashMap instead of a regular HashMap in a multithreaded environment?

ConcurrentHashMap should be used instead of a regular HashMap in a multithreaded environment when safe parallel access to the map is required without locking the entire structure.

A regular HashMap is not thread-safe and can lead to unpredictable behavior or data corruption when accessed concurrently by multiple threads.

ConcurrentHashMap implements efficient locking at the segment or bucket level, allowing multiple threads to read and write simultaneously with minimal locking.

Example usage:

import java.util.concurrent.ConcurrentHashMap;

ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();

// Thread 1
map.put("key1", 1);

// Thread 2
Integer value = map.get("key1");

Thus, ConcurrentHashMap provides safety and high performance in multithreaded applications where frequent access to a shared map is required.