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https://stackoverflow.com/questions/28834489/which-is-the-difference-between-atomicreference-and-synchronized/28837950#28837950

Prefer immutability whenever possible.
For code that can't be immutable, try to confine mutation to a thread.
If only one thing has to change across threads, use the atomic approach.
If multiple changes across threads need to occur together undisturbed by other threads, use locking.