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Groups > comp.lang.java.programmer > #10045

Re: alias for Integer

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jrobinss wrote:
> I am processing structures that contain integers, structures such as matrixes 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 relying on strong typing.
> 
> Usually, I would do this by extending the relevant class. But here it's Integer, which is final.

That is kind of an antipattern.  Joshua Bloch suggest to "Prefer composition to inheritance" in /Effective Java/ (2nd ed.).  You could write a wrapper for 'Integer', but then 'Integer' already *is* a wrapper type.

> Questions: 
> 1. is this a bad good idea, and I should proceed with Integer?

It's not a terrible idea, necessarily, but it seems unnecessary. 

> 2. if not, how would you implement this?

I would pick a type that actually helps.  I don't see what you object to in 'Integer', quite frankly.

> 3. is there any performance issue in defining my own classes instead of Integer?

How could anyone possibly know the answer to this question?

> 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;}
> }

Congratulations, you just re-invented 'Integer', but without any of its features.

Now you have to go through all sorts of gyrations to translate your custom class to and from 'int'.  Your code complexity goes up, and you have to maintain your own custom substitute for a fundamental API type.  Thus your risk of bugs and code-maintenance costs skyrocket.

How again does this help you?

> I won't benefit from autoboxing, then... :-(

No one does.

> (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)

Why waste *any* time on this?  Just use 'Integer'.

> 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 too much memory at the moment. I'm starting to optimize it, that's why I'm starting with strongly typing it to prevent errors.

"Optimize" and "prevent errors" are, at best, orthogonal, and at worst (and typically in this kind of premature action) the former interferes with the latter.

Yet you say them in the same breath as though they were the same thing.

They aren't.

Your "strong typing" isn't, really.  'Integer' already is a strong type.

As for what you choose to "optimize", what evidence (that is, factual data derived from actual tests whose protocols are publicized) do you have that you are attacking the slow parts?

IOW, what /actual/ tests have you performed, and how did you control the variables like system load, HotSpot warmup and application load?

You have a performance problem.  So you decide to obfuscate random parts of your code base with zero foundation for your actions.  Now you have two problems.

-- 
Lew

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Thread

alias for Integer jrobinss <julien.robinson2@gmail.com> - 2011-11-18 06:50 -0800
  Re: alias for Integer markspace <-@.> - 2011-11-18 07:11 -0800
  Re: alias for Integer Roedy Green <see_website@mindprod.com.invalid> - 2011-11-18 07:32 -0800
  Re: alias for Integer Lew <lewbloch@gmail.com> - 2011-11-18 07:34 -0800
    Re: alias for Integer jrobinss <julien.robinson2@gmail.com> - 2011-11-18 08:26 -0800
      Re: alias for Integer Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-18 18:00 +0000
      Re: alias for Integer markspace <-@.> - 2011-11-18 10:17 -0800
      Re: alias for Integer Roedy Green <see_website@mindprod.com.invalid> - 2011-11-18 20:30 -0800
    Re: alias for Integer Roedy Green <see_website@mindprod.com.invalid> - 2011-11-18 20:23 -0800
  Re: alias for Integer Jim Janney <jjanney@shell.xmission.com> - 2011-11-18 13:14 -0700
  Re: alias for Integer Patricia Shanahan <pats@acm.org> - 2011-11-18 12:43 -0800
  Re: alias for Integer jrobinss <julien.robinson2@gmail.com> - 2011-11-21 01:50 -0800
  Re: alias for Integer Robert Klemme <shortcutter@googlemail.com> - 2011-11-21 20:58 +0100
  Re: alias for Integer David Lamb <dalamb@cs.queensu.ca> - 2011-11-21 15:38 -0500

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