Are arrays thread-safe in Java?

While you will not get an invalid state by changing arrays as you mention, you will have the same problem that happens when two threads are viewing a non volatile integer without synchronization (see the section in the Java Tutorial on Memory Consistency Errors). Basically, the problem is that Thread 1 may write a value in space i, but there is no guarantee when (or if) Thread 2 will see the change.

The class java.util.concurrent.atomic.AtomicIntegerArray does what you want to do.

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