How is thread safety implemented in Java for ConcurrentHashMap?

In Java, the ConcurrentHashMap class ensures thread safety through segmentation and modern synchronization mechanisms. In older versions (before Java 8), the map was divided into several segments (Segment), each of which was locked separately, allowing multiple threads to work with different segments simultaneously without locking the entire map.

Starting from Java 8, the implementation changed: it uses CAS (Compare-And-Swap) mechanisms and synchronization at the level of individual bins, as well as optimized operations using volatile fields and other low-level primitives. This allows insert, delete, and search operations to be performed without global locking, providing high performance and safety during concurrent access.

Example of using ConcurrentHashMap:

import java.util.concurrent.ConcurrentHashMap;

ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
map.put("key1", 1);
Integer value = map.get("key1");

Thus, thread safety is achieved through the internal data structure and the use of atomic operations, which helps avoid race conditions and locks at the collection level.