HashMap alternatives for memory-efficient data storage

Question

I\'ve currently got a spreadsheet type program that keeps its data in an ArrayList of HashMaps. You\'ll no doubt be shocked when I tell you that this hasn\'t proven ideal.

Answer 1

Chronicle Map could have overhead of less than 20 bytes per entry (see a test proving this). For comparison, java.util.HashMap's overhead varies from 37-42 bytes with -XX:+UseCompressedOops to 58-69 bytes without compressed oops (reference).

Additionally, Chronicle Map stores keys and values off-heap, so it doesn't store Object headers, which are not accounted as HashMap's overhead above. Chronicle Map integrates with Chronicle-Values, a library for generation of flyweight implementations of interfaces, the pattern suggested by Brian Agnew in another answer.