Java visibility: final static non-threadsafe collection changes after construction

I found the following code snippet in luaj and I started to doubt that if there is a possibility that changes made to the Map after it has been constructed might not be visible to other threads since there is no synchronization in place.

I know that since the Map is declared final, its initialized values after construction is visible to other threads, but what about changes that happen after that.

Some might also realize that this class is so not thread-safe that calling coerce in a multi-threaded environment might even cause infinite loop in the HashMap, but my question is not about that.

public class CoerceJavaToLua {
    static final Map COERCIONS = new HashMap(); // this map is visible to all threads after construction, since its final

    public static LuaValue coerce(Object paramObject) {
        ...;
        if (localCoercion == null) {
            localCoercion = ...;
            COERCIONS.put(localClass, localCoercion); // visible?
        }
        return ...;
    }

    ...
}

You're correct that changes to the Map may not be visible to other threads. Every method that accesses COERCIONS (both reading and writing) should be synchronized on the same object. Alternatively, if you never need sequences of accesses to be atomic, you could use a synchronized collection.

(BTW, why are you using raw types?)