Question

Lets say we have a class called CompHash with 30 different variables as follows:

   public class CompHash{
      private String abc1;
      private int sdf2;
             :
             :
      private float sgh30;
   }

and a similar class:

     public class CompHash{
         private HashMap diffVariables;
     }

In a situation where the number of variables that I will be needing varies from 1 to 30, which of the two would be better?

Answer 1

In general you should always prefer strongly typed CompHash (the first one). Not only it is safer, but it will also be significantly faster.

If you have a requirement to store arbitrary number of variables, HashMap might be a good choice. But remember you are sacrificing type-safety without much gain – HashMap will probably still occupy more memory as opposed to a single object with lots of nulls.

The only valid usage of HashMap is when you need to store arbitrary pairs (it is not clear whether variables/key names are constant in your case) of key -> value. But in this scenario I would recommend wrapping primitives with a class hierarchy having common ancestor and using Visitor pattern to avoid dangarous down-casts and ugly instanceof‘s.

BTW what problem are you actually solving? The data structure you need seems a bit exotic…