Memory-efficient sparse array in Java

Question

(There are some questions about time-efficient sparse arrays but I am looking for memory efficiency.)

I need the equivalent of a List or

Answer 1

I have saved my test case as jglick/inthashmap. The results:

HashMap size: 1017504
TIntObjectMap size: 853216
IntHashMap size: 846984
OpenIntObjectHashMap size: 760472