Am I understanding SoftReferences correctly?

Question

I have browsed the forum archives and various articles on SoftReference and garbage collection, but I'm not 100% sure I'm getting it.
I am trying to set up a primitive cache system for holding List<Double> objects that are retrieved from a database. I am planning on storing them in a Map<Integer, SoftReference<List<Double>>>, with the key serving as a permanent ID to lookup the appropriate list.
If my cache gives out a reference to the List<Double>, my understanding is that the List<Double> cannot be collected as long as that reference persists. What I am unsure of is whether the List<Double> could be collected if I only gave out a reference to one of the Double objects in the list. From what I've read, my hunch is that the answer is yes... could someone please tell me if I am correct?
Many thanks!
Edit: strange... the ">" bracket after SoftReference in my message is not visible in the editable text version

Answer 1

If my cache gives out a reference to the
List<Double>, my understanding is that the
List<Double> cannot be collected as long as that
reference persists. You are correct. If the program has a strong reference to the list, then the list won't be eligible for collection.
What I am unsure of is whether
the List<Double> could be collected if I only gave
out a reference to one of the Double objects in the
list. From what I've read, my hunch is that the
answer is yes... Again correct. The soft reference points to the list. If you give out a reference to something in the list, then there's no hard reference to the list, and it's eligible for collection.
Side comment: unless your lists are relatively large (a few thousand items or more), and you have a lot of them, then soft references really won't buy you much. For small objects, I've found that a fixed-size LRU cache was a better solution.