What is the correct way to represent and manipulate probabilities and percents in Java?

Question

When calculating and manipulating probabilities in Java, and then expressing them as percentages, what is the best data structure to use to represent them?

The native double and float don't seem like particularly ideal candidates, since they have odd rounding issues which can introduce errors when the rounding happens multiple times and gets compounded.

BigInteger works well for calculating permutations and combinations, and BigDecimal seems like it might be a good candidate for the non-integer values, but is there something more suited to dealing with percentages already?

Note: In this case, the probabilities being calculated are similar in nature to those involving decks of cards, but with hundreds of cards. For the more math-inclined, I'm specifically working with Multivariate Hypergeometric_distributions.

Are they always going to be integer percentages? If so, use an int. BigInteger is overkill because your number isn't going to be any bigger than what can fit in a normal integer. — Paul Tomblin, Oct 21 '11 at 19:18
No, the percentages will usually be in the range of [0,1], but will be displayed int a format like `23.29945%`. `BigInteger` is used for factorial calculations. — cdeszaq, Oct 21 '11 at 19:25

score 5 · Accepted Answer · edited May 23 '17 at 12:09

5

When it comes to probabilities, I would suspect you would benefit from working with fractions.

Have a look at this question:

Best way to represent a fraction in Java?

Otherwise I think BigDecimal is your best choice. Beware however of the java.lang.ArithmeticException: Non-terminating decimal expansion;

edited May 23 '17 at 12:09

Community

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answered Oct 21 '11 at 19:24

aioobe

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Keeping things as fractions until the last minute (and then switch to a percent) seems like it might be a good idea. +1 – cdeszaq Oct 21 '11 at 19:28
You won't have any rounding issues at least :) – aioobe Oct 21 '11 at 19:29

score 0 · Answer 2 · edited Dec 20 '11 at 13:56

This is what I would do with a double, I think that using a double would be the best for getting a good value with percent...

import java.text.NumberFormat;
//instance variable:
private static NumberFormat percent = NumberFormat.getPercentInstance();

//inside any method or event:
myAprValue = userInput / 100; 
percent = new DecimalFormat("0.0#%"); 

String st = percent.format(myAprValue);

What is the correct way to represent and manipulate probabilities and percents in Java?

2 Answers2