Question

Integer getElement( List<Integer> list ) {

   int i = Random.getInt( list.size() );

   return list.get( i );

}

The question: while this function has been called from a thread, IS there a way the list passed to this function can be modified by another thread?

Answer 1

No. java.util.List doesn’t guarantee thread safety. The list can be changed between list.size() and list.get() by another thread. Moreover memory inconsistency is also a problem.

I could think three ways to solve it:

1. Use immutable list. Collections.unmodifiableList(list) is fine, Guava’s ImmuntableList is better.
2. Synchronized the list. but you have to synchronize the list instance all over the program.
3. List in java.util.concurrent. It’s a sophisticated concurrency solution.