Thread: Bitstrings vs Hashmap

Hi everyone,

I have a bit of a problem that I've been trying to figure out for a while now, so any new input would be helpful and greatly appreciated.

One of the things I'm working on is to determine the state of an object. For example, an object could be a fruit, colour red, with skin and sweet, while another object could have four legs, made of wood, and is located in your kitchen. The problem I have is that any given object can have any given pre-defined states, I won't know until runtime as to how many pre-defined states there are. It could be anywhere from 1-1000, let's say, and I could have more than 100k objects in memory. So speed and memory is a bit of an issue.

Now, one of the ways to do it is with bitstrings manipulation. An "AND" will be able to tell me whether that particular flag is set or not. I guess my question is: would I be saving myself a lot of grief if i just made a hashmap with the value (say, {colour.red, 1}) and checked for that.

Thanks

If you are not going to know the number of pre-defined states at runtime a HashMap may be very useful. You may wish to use a HashSet rather than a Map - because it implements the Set interface (which extends Collection) it may give you more of an advantage when doing things that require a Collection (like comparisons - although HashSet uses a HashMap as its foundation, it directly implements the Set/Collection interface whereas the Map does not).

I'm going to have to read up on the difference between a HashSet and a HashMap ... thanks!

Here is a definition of HashSet vs HashMap:

A HashMap provides fast access to a mapping from a unique key to a value. Keys are unordered, which makes it faster than the TreeMap, where the keys are ordered. A HashSet is fast access to unique values only (there are no keys because it is not a mapping, it's just the values). HashSet values are unordered, which makes it faster than the TreeSet, where the values are ordered. (Core Java - What is the difference between hashmap and hashset?)

I guess in my case, I could just use HashSet because they're not in order, and the existance of those unique values already mean that the flag is set. Thanks!