BigDecimal in Java

Question

I am thinking of using BigDecimal to compare two currency values rounded to 2 digits. For example I expect the following to yield 0 because I'm comparing something that should round to 0.02 with something that is 0.02. But it yields -1 !! Is there a right way to do this?

This should also work for larger numbers like 123.45 vs 123.4534 ... which should yield 0 when "compareTo" is used.

I've tried using math context but it doesnt seem elegant ... is there a correct way?

BigDecimal spread = new BigDecimal(0.01934);
spread.setScale(2, RoundingMode.HALF_EVEN);
System.out.format("0.0193 ? 0.02 = %d\n", spread.compareTo(new BigDecimal(0.02)));

AND THE SOLUTION IS:

BigDecimal spread = new BigDecimal(0.01934).setScale(2, RoundingMode.HALF_EVEN);
BigDecimal loSpread = new BigDecimal(0.02).setScale(2, RoundingMode.HALF_EVEN);
System.out.format("0.0193 ? 0.02 = %d\n", spread.compareTo(loSpread));

class stacker · Accepted Answer · 2013-04-23 09:40:36Z

10

First off, BigDecimal is immutable. You must return the result from your setScale method call:

spread = spread.setScale(2, RoundingMode.HALF_EVEN);

Next you must improve your accuracy of the second BigDecimal since it is being derived from a double -- not a very accurate entity. So try a String:

 spread.compareTo(new BigDecimal("0.02"))

edited Apr 23, 2013 at 9:40

class stacker

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answered Jun 24, 2012 at 2:04

Hovercraft Full Of Eels

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3 Comments

fodon Over a year ago

This is actually used to compare prices. They may have to be instantiated from doubles.

Hovercraft Full Of Eels Over a year ago

@fodon: Then user unknown has part of your answer for you, and I have the other part (regarding BigDecimal being immutable).

class stacker Over a year ago

I reverted the invalid edit. Folks, please comment or provide an additional answer if you aren't satisfied with an answer you see.

Peter Lawrey · Accepted Answer · 2012-06-24 09:35:34Z

5

0.02 gets evaluated to

java.math.BigDecimal = 0.0200000000000000004163336342344337026588618755340576171875

You have to setScale(2, RoundingMode.HALF_EVEN) there too.

edited Jun 24, 2012 at 9:35

Peter Lawrey

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answered Jun 24, 2012 at 2:13

user unknown

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2 Comments

Hovercraft Full Of Eels Over a year ago

That's another way to get an accurate floating point number. 1+.

fodon Over a year ago

Had to use both ideas here to get it right. Will post correct code.

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