Does the HashMap class ensure safety when used in a multithreaded environment?

The HashMap class in Java is not thread-safe. If multiple threads modify a HashMap simultaneously without external synchronization, it can lead to unpredictable behavior, including data loss or infinite loops.

To use it in a multithreaded environment, you can:

• Use Collections.synchronizedMap(new HashMap<>()) — which wraps the HashMap in a synchronized version.
• Use the ConcurrentHashMap class, which is specifically designed for safe operation with multiple threads without full locking.

Example of using ConcurrentHashMap:

import java.util.concurrent.ConcurrentHashMap;

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

Thus, for multithreaded work, it is better to use ConcurrentHashMap or manually synchronize access to the HashMap.