How does ArrayList work in a multithreaded environment?

How does ArrayList work in a multithreaded environment?

In a multithreaded environment, ArrayList is not thread-safe. This means that if multiple threads access an ArrayList concurrently, and at least one of the threads modifies the list, it must be synchronized externally.

What are the risks of using ArrayList without synchronization?

The main risks include data inconsistency, unexpected behavior, and potential ConcurrentModificationException if one thread modifies the list while another is iterating over it.

What alternatives do I have for thread-safe collections?

You can use Vector, which is synchronized, or consider using Collections.synchronizedList to wrap an ArrayList. Additionally, Java's CopyOnWriteArrayList is a good option for scenarios with more reads than writes.

Can you explain how CopyOnWriteArrayList works?

CopyOnWriteArrayList creates a new copy of the underlying array on each write operation, making it thread-safe for concurrent reads. This is efficient for scenarios with many reads and few writes.