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

keeps its data in an ArrayList of HashMaps
Well, this part seems terribly inefficient to me. Empty HashMap will already allocate 16 * size of a pointer bytes (16 stands for default initial capacity), plus some variables for hash object (14 + psize). If you have a lot of sparsely filled rows, this could be a big problem.

One option would be to use a single large hash with composite key (combining row and column). Although, that doesn't make operations on whole rows very effective.

Also, since you don't mention the operation of adding cell, you can create hashes with only necessary inner storage (initialCapacity parameter).

I don't know much about google collections, so can't help there. Also, if you find any useful optimization, please do post here! It would be interesting to know.