Representing an extremely small number in java?

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adam.balgach@gmail.com - 07 Dec 2006 19:04 GMT

I have a requirement to represent a very very small number in a java
class of mine:

2.2204e-16

Does anyone have a straightforward solution to doing this? or am i
stuck with writing out something like

double _a = 0.0000000000000000....222204;

?

Thanks in advance,
A.

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mearvk - 07 Dec 2006 19:10 GMT

Check out this API:
http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html

I believe you can create arbitrarily small/precise decimals using an
implementation of this class.

mearvk

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Andreas Wollschlaeger - 07 Dec 2006 19:31 GMT

> I have a requirement to represent a very very small number in a java
> class of mine:
[quoted text clipped - 10 lines]
> Thanks in advance,
> A.

How about

double a = 2.2204e-16d;

where the final 'd' makes sure it is a double literal; otherwise it
would be a 'real', implicitly casted to a 'double'!

Life can be that easy....

HTH
Andreas

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Mark Thornton - 07 Dec 2006 20:13 GMT

>> I have a requirement to represent a very very small number in a java
>> class of mine:
[quoted text clipped - 17 lines]
> where the final 'd' makes sure it is a double literal; otherwise it
> would be a 'real', implicitly casted to a 'double'!

You don't need the 'd' suffix --- floating point values are double by
default. So this suffices

double a = 2.2204e-16;

By contrast you do need the 'f' suffix here:

float a = 2.2204e-16f;

Mark Thornton

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EJP - 07 Dec 2006 23:35 GMT

> double a = 2.2204e-16d;
>
> where the final 'd' makes sure it is a double literal; otherwise it
> would be a 'real', implicitly casted to a 'double'!

What's a 'real'? The 'e' is enough to mark it as a double, you don't
need the 'd' as well.

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mearvk - 08 Dec 2006 00:48 GMT

I should also add that since decimals are continuous (and the mapping
onto them is not), you only get a certain degree of accuracy using
Java's doubles. A double is 64 bits, which is quite alot. But remember,
there are an infinite number of decimals values between 0 and 1. So
when you do a comparison between two very small numbers which are
*similar*, the JVM may consider them to be equal, when in fact they are
not. This is where the BigDecimal implementation is a better solution.

May be germane, or not.

Mearvk

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Representing an extremely small number in java?

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