Which collections from java.util.concurrent are suitable for multithreaded work? How do they differ from regular collections?

The java.util.concurrent package contains several collections specifically designed for safe operation in a multithreaded environment. The main ones are:

• ConcurrentHashMap — a thread-safe version of HashMap that allows multiple threads to read and write simultaneously without locking the entire structure.
• CopyOnWriteArrayList — a list where each modification creates a new copy of the array, ensuring safe reading without locks but with write costs.
• ConcurrentLinkedQueue — a non-blocking linked list-based queue suitable for multithreaded access.
• BlockingQueue (e.g., LinkedBlockingQueue, ArrayBlockingQueue) — queues with blocking support that allow threads to wait for elements to appear or space to become available.

Differences from regular collections:

• They ensure correct operation during concurrent access from multiple threads without external synchronization.
• Use internal synchronization mechanisms or non-blocking algorithms to improve performance.
• Help avoid race conditions and exceptions like ConcurrentModificationException.

Example of using ConcurrentHashMap:

ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
map.put("key", 1);
map.computeIfPresent("key", (k, v) -> v + 1);
System.out.println(map.get("key")); // 2