Solved

numeric representation/precision error

Posted on 1997-06-19
1
214 Views
Last Modified: 2008-03-10
I am relatively new to the java programming world, and having a really annoying problem with this piece of code:

import java.io.*;

class doubleTest {
    public static void main(String argv[]) {
        double sigDigits = 9.74;
        double shiftLeft = 9.0;  // number of places to                                         shift decimal left

        for (int i = 1; i <= shiftLeft; i++) {
            sigDigits = sigDigits/10.0;
            System.out.println(sigDigits);
        }
    }
}


this produces the following output:
0.974
0.0974
0.00974
9.74E-4
9.740000000000001E-5
9.740000000000002E-6
9.740000000000001E-7
9.740000000000001E-8
9.740000000000002E-9  // I get this number also if I                                  substitute for loop with:
    sigDigits = Math.pow(sigDigits,-shiftLeft);


Why the extra digit at the end of the number?  Is there a better way to divide doubles that don't produce erroneous output?  If you change shiftLeft to 19.0,
you get the following output:
0.974
0.0974
0.00974
9.74E-4
9.740000000000001E-5
9.740000000000002E-6
9.740000000000001E-7
9.740000000000001E-8
9.740000000000002E-9
9.740000000000002E-10
9.740000000000002E-11
9.740000000000002E-12
9.74E-13
9.740000000000001E-14
9.740000000000001E-15
9.74E-16
9.74E-17
9.74E-18
9.74E-19

this is very strange to me.  Thanks in advance for you help.
-Matt
0
Comment
Question by:mclaren
1 Comment
 
LVL 6

Accepted Solution

by:
jpk041897 earned 50 total points
ID: 1221833
All floating point libraries introduce presition errors, the good ones simply produce them less often. Unfortunatley Java's FP lib is not amongst the best.

There are 3 possible work arrounds:

1.- If the error affect your results somhow, you will have to use native methods. See:

http://www.inf.uni-hohenheim.de/top/java/tutorial/native1.1/index.html

on how to use them.

2.- If the error only affects your results for display purposes (I.e.: the accumulated effect of the errors does not affect the values you wish to display), use formatting classes on the  output to get rid of the error. See:

http://www.acme.com/java/software/Acme.Fmt.html

for a class that will allow you to do this.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction Java can be integrated with native programs using an interface called JNI(Java Native Interface). Native programs are programs which can directly run on the processor. JNI is simply a naming and calling convention so that the JVM (Java…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
Viewers learn about the “for” loop and how it works in Java. By comparing it to the while loop learned before, viewers can make the transition easily. You will learn about the formatting of the for loop as we write a program that prints even numbers…
This tutorial explains how to use the VisualVM tool for the Java platform application. This video goes into detail on the Threads, Sampler, and Profiler tabs.

937 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

5 Experts available now in Live!

Get 1:1 Help Now