alias for Integer

Hi all,

this is a simple question, so it may be silly...

I am processing structures that contain integers, structures such as matrix=
es used in statistical analysis. As I implement these as Maps of indexes, I=
 use the class Integer, as in

  // Map<matrix index, DB index> <- I'd like to remove this comment!
  public static Map<Integer, Integer> myMap = ...;

Now what I'd like is to write
  public static Map<MatrixIndex, DbIndex> myMap = ...;

The advantage is that the code is auto-documented, but even better that the=
 compiler will check that I never get mixed up in different indexes, by rel=
ying on strong typing.

Usually, I would do this by extending the relevant class. But here it's Int=
eger, which is final.

Questions:
1. is this a bad good idea, and I should proceed with Integer?
2. if not, how would you implement this?
3. is there any performance issue in defining my own classes instead of Int=
eger?

My current solution is to define my own classes for replacing Integer, such=
 as:

public final class MatrixIndex {
  public final int value;
  public MyIndex(int i) {value = i;}
}

I won't benefit from autoboxing, then... :-(
(I'm just hoping it doesn't break too much of the code, because even though=
 it's mine to break, I don't have infinite time)

Note that (exceptionnally for me) performance *is* an issue here. I haven't=
 yet narrowed it down, but the code executes very slowly and eats up much t=
oo much memory at the moment. I'm starting to optimize it, that's why I'm s=
tarting with strongly typing it to prevent errors.

thanks for any tips!
JRobinss